- Ruhr-Universität Bochum

BACKGROUND: Sodium chlorate (NaClO3) is extensively used in the paper industry, but its production uses strictly regulated highly toxic Na2Cr2O7 to reach high hydrogen evolution reaction (HER) Faradaic efficiencies. It is therefore important to find alternatives either to replace Na2Cr2O7 or reduce its concentration. RESULTS: The Na2Cr2O7 concentration can be significantly reduced by using Na2MoO4 as an electrolyte co-additive. Na2MoO4 in the millimolar range shifts the platinum cathode potential to less negative values due to an activating effect of cathodically deposited Mo species. It also acts as a stabilizer of the electrodeposited chromium hydroxide but has a minor effect on the HER Faradaic efficiency. X-ray photoelectron spectroscopy (XPS) results show cathodic deposition of molybdenum of different oxidation states, depending on deposition conditions. Once Na2Cr2O7 was present, molybdenum was not detected by XPS, as it is likely that only trace levels were deposited. Using electrochemical measurements and mass spectrometry we quantitatively monitored H2 and O2 production rates. The results indicate that 3 μmol L−1 Na2Cr2O7 (contrary to current industrial 10–30 mmol L−1) is sufficient to enhance the HER Faradaic efficiency on platinum by 15%, and by co-adding 10 mmol L−1 Na2MoO4 the cathode is activated while avoiding detrimental O2 generation from chemical and electrochemical reactions. Higher concentrations of Na2MoO4 led to increased oxygen production. CONCLUSION: Careful tuning of the molybdate concentration can enhance performance of the chlorate process using chromate in the micromolar range. These insights could be also exploited in the efficient hydrogen generation by photocatalytic water splitting and in the remediation of industrial wastewater. © 2023 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI). © 2023 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Catalysis is involved in around 85 % of manufacturing industry and contributes an estimated 25 % to the global domestic product, with the majority of the processes relying on heterogeneous catalysis. Despite the importance in different global segments, the fundamental understanding of heterogeneously catalysed processes lags substantially behind that achieved in other fields. The newly established Max Planck–Cardiff Centre on the Fundamentals of Heterogeneous Catalysis (FUNCAT) targets innovative concepts that could contribute to the scientific developments needed in the research field to achieve net zero greenhouse gas emissions in the chemical industries. This Viewpoint Article presents some of our research activities and visions on the current and future challenges of heterogeneous catalysis regarding green industry and the circular economy by focusing explicitly on critical processes. Namely, hydrogen production, ammonia synthesis, and carbon dioxide reduction, along with new aspects of acetylene chemistry. © 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.

Proton transfer is vital for many biological and chemical reactions. Hydrogen-bonded water-containing networks are often found in enzymes to assist proton transfer, but similar strategy has been rarely presented by synthetic catalysts. We herein report the Co corrole 1 with an appended crown ether unit and its boosted activity for the hydrogen evolution reaction (HER). Crystallographic and 1H NMR studies proved that the crown ether of 1 can grab water via hydrogen bonds. By using protic acids as proton sources, the HER activity of 1 was largely boosted with added water, while the activity of crown-ether-free analogues showed very small enhancement. Inhibition studies by adding 1) external 18-crown-6-ether to extract water molecules and 2) potassium ion or N-benzyl-n-butylamine to block the crown ether of 1 further confirmed its critical role in assisting proton transfer via grabbed water molecules. This work presents a synthetic example to boost HER through water-containing networks. © 2021 Wiley-VCH GmbH

The vision to replace coal with hydrogen goes back to Jules Verne in 1874. However, sustainable hydrogen production remains challenging. The most elegant approach is to utilize photosynthesis for water splitting and to subsequently save solar energy as hydrogen. Cyanobacteria and green algae are unicellular photosynthetic organisms that contain hydrogenases and thereby possess the enzymatic equipment for photosynthetic hydrogen production. These features of cyanobacteria and algae have inspired artificial and semi-artificial in vitro techniques, that connect photoexcited materials or enzymes with hydrogenases or mimics of these for hydrogen production. These in vitro methods have on their part been models for the fusion of cyanobacterial and algal hydrogenases to photosynthetic photosystem I (PSI) in vivo, which recently succeeded as proofs of principle. © 2022 The Author(s)

The reduction of iron ore with carbon-carriers is one of the largest sources of greenhouse gas emissions in the industry, motivating global activities to replace the coke-based blast furnace reduction by hydrogen-based direct reduction (HyDR). Iron oxide reduction with hydrogen has been widely investigated both experimentally and theoretically. The HyDR process includes multiple types of chemical reactions, solid state and defect-mediated diffusion (of oxygen and hydrogen species), several phase transformations, as well as massive volume shrinkage and mechanical stress buildup. However, studies focusing on the chemo-mechanical interplay during the reduction reaction influenced by microstructure are sparse. In this work, a chemo-mechanically coupled phase-field (PF) model has been developed to explore the interplay between phase transformation, chemical reaction, species diffusion, large elasto-plastic deformation and microstructure evolution. Energetic constitutive relations of the model are based on the system free energy which is calibrated with the help of a thermodynamic database. The model has been first applied to the classical core-shell (wüstite-iron) structure. Simulations show that the phase transformation from wüstite to α-iron can result in high stresses and rapidly decelerating reaction kinetics. Mechanical stresses create elastic energy in the system, an effect which can negatively influence the phase transformations, thus causing slow reaction kinetics and low metallization. However, if the elastic stress becomes comparatively high, it can shift the shape of the free energy from a double-well to a single-well case, speed up the transformation and result in a higher reduction degree compared to the low-stress double-well case. The model has been applied to simulate an experimentally characterized iron oxide specimen with its complex microstructure. The observed microstructure evolution during reduction is well predicted by the model. The simulation results also show that isolated pores in the microstructure are filled with water vapor during reduction, which can influence the local reaction atmosphere and dynamics. © 2022

Hydrogen production via plasma methane pyrolysis is investigated using a microwave plasma torch (MPT) and a gliding arc plasmatron (GAP). The performance of the two plasma sources in terms of methane conversion, product spectrum, and energy efficiency is compared. The physical and chemical properties of the produced carbon particles are compared. The methane conversion is higher in the GAP than in the MPT. In the MPT amorphous spherical carbon particles are produced in the volume of the plasma source. In the GAP methane pyrolysis in the volume stops after the production of acetylene. The conversion of acetylene into solid carbon takes place in a heterogeneous reaction on top of the electrode surfaces instead. This leads to a lower hydrogen selectivity, higher acetylene selectivity and more platelet-like morphology of the produced carbon particles when compared to the MPT. © 2022 The Authors. Plasma Processes and Polymers published by Wiley-VCH GmbH.

Halogen bonding has recently been recognized as an interaction whose relevance is on par with hydrogen bonding. While observed frequently in solution chemistry, the significance of halogen bonds in forming extended supramolecular structures on surfaces is less explored. Herein, we report on the self-assembly of chlorobenzene molecules adsorbed on the Cu(111) surface into nanosized clusters at submonolayer coverages, where the molecular planes are close to parallel to the surface. A comprehensive study of the role of intermolecular interactions through both halogen and weak hydrogen bonds on nanocluster formation is presented, gained by combining the results of temperature-programmed desorption, reflection-absorption infrared spectroscopy, scanning tunneling microscopy, and density functional theory calculations. Based on an unprecedented precise determination of the molecules’ orientation within the clusters, the binding motifs that lead to the formation and stability of nanoclusters with magic sizes are identified and explained. A complex and delicate interplay of halogen bonds with weak hydrogen bonds, van-der-Waals forces, and surface–adsorbate interactions leads to a preference for hexamers and tetramers with an observable propensity for halogen bonding over weak hydrogen bonding when adsorbed to the Cu(111) surface. © 2021 American Chemical Society

Scanning tunneling microscopy (STM) and density functional theory (DFT) were used to study the tautomerization reaction of an H2Pc molecule adsorbed on a Ag(100) surface. The presence of two hydrogen atoms in the cavity of the H2Pc molecule enforces the existence of two molecular tautomers. It causes a reduction from 4- to 2-fold symmetry in STM images that can be recorded as two current states over the H2Pc molecule with a high-to-low current state ratio of ∼1.2. These findings are confirmed by the spatial distributions of the all-atom electron charge density calculated by using DFT and transmission maps together with tunneling current ratios (∼1.2) determined from the nonequilibrium Green's function transport calculations. Therefore, we demonstrate that an H2Pc molecule adsorbed on a Ag(100) surface is a good candidate for a bistable molecular conductance switch since neither the presence of the Ag(100) surface nor that of the STM tip alters the tautomerization. © 2022 American Chemical Society.

Fossil-free ironmaking is indispensable for reducing massive anthropogenic CO2 emissions in the steel industry. Hydrogen-based direct reduction (HyDR) is among the most attractive solutions for green ironmaking, with high technology readiness. The underlying mechanisms governing this process are characterized by a complex interaction of several chemical (phase transformations), physical (transport), and mechanical (stresses) phenomena. Their interplay leads to rich microstructures, characterized by a hierarchy of defects ranging across several orders of magnitude in length, including vacancies, dislocations, internal interfaces, and free surfaces in the form of cracks and pores. These defects can all act as reaction, nucleation, and diffusion sites, shaping the overall reduction kinetics. A clear understanding of the roles and interactions of these dynamically-evolving nano-/microstructure features is missing. Gaining better insights into these effects could enable improved access to the microstructure-based design of more efficient HyDR methods, with potentially high impact on the urgently needed decarbonization in the steel industry. © 2022 The Author(s)

Selective photocatalytic oxidation of alcohols into value-added aldehydes or ketones is a promising alternative for alcohol oxidation concerning the mild reaction conditions and the controllable selectivity. To increase the activity, defective Bi2WO6 with abundant oxygen vacancies (OVs) was synthesized via substitution of W by Ta. The resulting Ta-doped Bi2WO6 loaded with Pt nanoparticles as co-catalyst efficiently converted aromatic and aliphatic alcohols into the corresponding carbonyl compounds with high selectivity (>99%) in aqueous solution under visible-light irradiation and anaerobic conditions, with equivalent H2 as a coupled product. The optimal amount of benzyl alcohol converted by the Ta-doped catalyst was two times higher than that of the undoped catalyst. Surface OVs were found to favor the dissociative adsorption of the alcohols and to prolong the life time of the charge carriers. More importantly, isotopic labelling experiments confirmed that over Pt-loaded pristine undoped Bi2WO6, the coupled H2 product results from water reduction, while over Pt-loaded Ta-doped Bi2WO6, the produced H2 originates from benzyl alcohol, implying that benzyl alcohol can be photo-oxidized via a complete dehydrogenation pathway. Thus, enriched surface OVs in photocatalysts can activate α-C-H bonds in alcohols, boosting the photocatalytic oxidation performance. © 2021 Elsevier B.V.

Using high-pressure methanol and methyl formate pulses as a surface-sensitive operando method for high-pressure methanol synthesis over Cu/ZnO/Al2O3, the recently found autocatalytic pathway was confirmed. The autocatalytic effect is assumed to result from the faster hydrogenation of the formed methyl formate ester at high methoxy coverages compared with the rate-determining hydrogenation of formate to dioxomethylene. When pulsing increasing amounts of methanol at 60 bar and 210 °C under kinetically controlled conditions in 13.5 vol% CO, 3.5 vol% CO2, and 73.5 vol% H2, higher amounts of methanol were observed in response. The surplus of formed methanol was found to increase exponentially as a function of the dosed amount of methanol and the applied residence time. To further investigate the methanol-assisted autocatalytic pathway, methyl formate as the predicted intermediate was pulsed, which was rapidly converted into methanol. Instead of the expected 2 : 1 stoichiometry of methanol : methyl formate, only one methanol molecule was produced per dosed methyl formate molecule. It is concluded that methyl formate is split into methoxy and formate species by dissociative adsorption, but only methoxy species are rapidly further hydrogenated to desorbing methanol, whereas formate hydrogenation to methanol is too slow on the time scale of the pulse experiments. © 2022 The Royal Society of Chemistry.

Steel production causes a third of all industrial CO2 emissions due to the use of carbon-based substances as reductants for iron ores, making it a key driver of global warming. Therefore, research efforts aim to replace these reductants with sustainably produced hydrogen. Hydrogen-based direct reduction (HyDR) is an attractive processing technology, given that direct reduction (DR) furnaces are routinely operated in the steel industry but with CH4 or CO as reductants. Hydrogen diffuses considerably faster through shaft-furnace pellet agglomerates than carbon-based reductants. However, the net reduction kinetics in HyDR remains extremely sluggish for high-quantity steel production, and the hydrogen consumption exceeds the stoichiometrically required amount substantially. Thus, the present study focused on the improved understanding of the influence of spatial gradients, morphology, and internal microstructures of ore pellets on reduction efficiency and metallization during HyDR. For this purpose, commercial DR pellets were investigated using synchrotron high-energy X-ray diffraction and electron microscopy in conjunction with electron backscatter diffraction and chemical probing. Revealing the interplay of different phases with internal interfaces, free surfaces, and associated nucleation and growth mechanisms provides a basis for developing tailored ore pellets that are highly suited for a fast and efficient HyDR. © 2022, The Author(s).

Advanced lightweight high-strength steels are often compositionally and microstructurally complex. While this complex feature enables the activation of multiple strengthening and strain-hardening mechanisms, it also leads to a complicated damage behavior, especially in the presence of hydrogen (H). The mechanisms of hydrogen embrittlement (HE) in these steels need to be properly understood for their successful application. Here we focus on a high-Mn (∼20 wt.%), high-Al (∼9 wt.%) lightweight steel with an austenite (∼74 vol.%) and ferrite (∼26 vol.%) two-phase microstructure and unravel the interplay of H-related decohesion and localized plasticity and their effects on failure. We find that HE in this alloy is driven by both, H-induced intergranular cracking along austenite-ferrite phase boundaries and H-induced transgranular cracking inside the ferrite. The former phenomenon is attributed to the mechanism of H-enhanced decohesion. For the latter damage behavior, systematic scanning electron microscopy-based characterization reveals that only parts of the transgranular cracks inside ferrite are straight (∼52% proportion) and along the cleavage plane. Other portions of these transgranular cracks show a distinct deviation from the {100} planes at certain stages of crack propagation, which is associated with a mechanism transition from the H-enhanced transgranular decohesion of the ferrite by cleavage to the H-associated localized plasticity occurring near the propagating crack tip. These mechanisms are further discussed based on a detailed comparison to the damage behavior at cryogenic temperatures and on the nanoindentation results performed with in-situ H-charging. The findings provide new insights into the understanding of the interplay between different HE mechanisms operating in high-strength alloys and their synergistic effects on damage evolution. © 2022 Acta Materialia Inc.

While age-hardened austenitic high-Mn and high-Al lightweight steels exhibit excellent strength-ductility combinations, their properties are strongly degraded when mechanically loaded under harsh environments, e.g. with the presence of hydrogen (H). The H embrittlement in this type of materials, especially pertaining to the effect of κ-carbide precipitation, has been scarcely studied. Here we focus on this subject, using a Fe-28.4Mn-8.3Al-1.3C (wt%) steel in different microstructure conditions, namely, solute solution treated and age-hardened. Contrary to the reports that grain boundary (GB) κ-carbides precipitate only during overaging, site-specific atom probe tomography and scanning transmission electron microscopy (STEM) reveal the existence of nanosized GB κ-carbides at early stages of aging. We correlate this observation with the deterioration of H embrittlement resistance in aged samples. While H pre-charged solution-treated samples fail by intergranular fracture at depths consistent with the H ingress depth (∼20 µm), age-hardened samples show intergranular fracture features at a much larger depth of above 500 µm, despite similar amount of H introduced into the material. This difference is explained in terms of the facile H-induced decohesion of GB κ-carbides/matrix interfaces where H can be continuously supplied through internal short-distance diffusion to the propagating crack tips. The H-associated decohesion mechanisms are supported by a comparison with the fracture behavior in samples loaded under the cryogenic temperature and can be explained based on dislocation pileups and elastic misfit at the GB κ-carbide/matrix interfaces. The roles of other plasticity-associated H embrittlement mechanisms are also discussed in this work based on careful investigations of the dislocation activities near the H-induced cracks. Possible alloying and microstructure design strategies for the enhancement of the H embrittlement resistance in this alloy family are also suggested. © 2022

Ever more stringent regulations on greenhouse gas emissions from transportation motivate efforts to revisit materials used for vehicles1. High-strength aluminium alloys often used in aircrafts could help reduce the weight of automobiles, but are susceptible to environmental degradation2,3. Hydrogen ‘embrittlement’ is often indicated as the main culprit4; however, the exact mechanisms underpinning failure are not precisely known: atomic-scale analysis of H inside an alloy remains a challenge, and this prevents deploying alloy design strategies to enhance the durability of the materials. Here we performed near-atomic-scale analysis of H trapped in second-phase particles and at grain boundaries in a high-strength 7xxx Al alloy. We used these observations to guide atomistic ab initio calculations, which show that the co-segregation of alloying elements and H favours grain boundary decohesion, and the strong partitioning of H into the second-phase particles removes solute H from the matrix, hence preventing H embrittlement. Our insights further advance the mechanistic understanding of H-assisted embrittlement in Al alloys, emphasizing the role of H traps in minimizing cracking and guiding new alloy design. © 2022, The Author(s).

The development of electrodes for efficient CO2reduction while forming valuable compounds is critical. The use of enzymes as catalysts provides the advantage of high catalytic activity in combination with highly selective transformations. We describe the electrical wiring of a carbon monoxide dehydrogenase II from Carboxydothermus hydrogenoformans (ChCODH II) using a cobaltocene-based low-potential redox polymer for the selective reduction of CO2to CO over gas diffusion electrodes. High catalytic current densities of up to -5.5 mA cm-2are achieved, exceeding the performance of previously reported bioelectrodes for CO2reduction based on either carbon monoxide dehydrogenases or formate dehydrogenases. The proposed bioelectrode reveals considerable stability with a half-life of more than 20 h of continuous operation. Product quantification using gas chromatography confirmed the selective transformation of CO2into CO without any parasitic co-reactions at the applied potentials. © 2022 American Chemical Society. All rights reserved.

The non-oxidative dehydrogenation of methanol to formaldehyde is considered a dream reaction compared with the classical oxidative route, because the valuable coupled product hydrogen is formed instead of water, and the produced anhydrous formaldehyde is highly suitable for the further synthesis of oxygenated synthetic fuels. This study reports on the high catalytic performance of pure β-Ga2O3 in this reaction at temperatures between 500 °C and 650 °C. At 550 °C and a GHSV of 45500 h−1, an initial selectivity to formaldehyde of 77 % was obtained at a methanol conversion of 72 %. Performing the reaction at temperatures beyond this range and lower GHSV resulted in a lower formaldehyde selectivity. The catalyst suffered from deactivation caused by formation of carbon deposits, but it was possible to regenerate its initial activity at 500 °C and 550 °C completely by an oxidative treatment. Irreversible deactivation occurred at 650 °C due to partial volatilization of Ga2O3. © 2022 The Authors. ChemCatChem published by Wiley-VCH GmbH.

The reaction pathways of higher alcohol synthesis over a bulk Co−Cu catalyst (Co : Cu=2 : 1) were investigated by applying high-pressure pulse experiments as a surface-sensitive operando method at 280 °C and 60 bar. Using high-pressure CO and H2 pulses in a syngas flow with a H2:CO ratio of 1, it was shown that the surface of the working 2CoCu catalyst is saturated with adsorbed CO, but not with adsorbed atomic hydrogen, because only the H2 pulses increased the yields of all alcohols and alkanes. The reverse water gas shift reaction (WGSR) was investigated by pulsing CO2. The CO2 pulses poisoned the formation of methanol, ethanol, and 1-propanol, and the absence of significant CO and H2O responses indicates that the WGSR is not efficiently catalyzed by the applied 2CoCu catalyst excluding the presence of exposed Cu0 sites. A series of ethylene pulses showed that when a threshold mole fraction of ethylene of about 1 vol % is surpassed, 2CoCu is an active catalyst for the hydroformylation of ethylene to 1-propanol pointing to the presence of highly coordinatively unsaturated Co sites. © 2022 The Authors. ChemCatChem published by Wiley-VCH GmbH.

Water diffusion across the surfaces of materials is of importance to disparate processes such as water purification, ice formation, and more. Despite reports of rapid water diffusion on surfaces the molecular level, details of such processes remain unclear. Here, with scanning tunneling microscopy, we observe structural rearrangements and diffusion of water trimers at unexpectedly low temperatures (<10 K) on a copper surface, temperatures at which water monomers or other clusters do not diffuse. Density functional theory calculations reveal a facile trimer diffusion process involving transformations between elongated and almost cyclic conformers in an inchworm-like manner. These subtle intermolecular reorientations maintain an optimal balance of hydrogen-bonding and water–surface interactions throughout the process. This work shows that the diffusion of hydrogen-bonded clusters can occur at exceedingly low temperatures without the need for hydrogen bond breakage or exchange; findings that will influence Ostwald ripening of ice nanoclusters and hydrogen bonded clusters in general. © 2021 American Chemical Society

To better understand why amines catalyze the reactivity of SiOH with silanes, we examined the adsorption of trimethylamine under a low pressure (10-9-10-8 mbar) and a low temperature (105-160 K) on water-terminated (H,OH)-Si(001), which is both a model surface for adsorption studies and a promising starting substrate for atomic layer deposition. Trimethylamine bonding configurations were determined by combining real-time synchrotron radiation X-ray photoelectron spectroscopy (XPS) and high-resolution electron energy loss spectroscopy (HREELS) with density functional theory (DFT) calculations of core-level ionization energies and vibrational spectra. Both spectroscopies showed that the majority of species are trimethylamine molecules making acceptor H bonds with surface hydroxyls. Moreover, HREELS indicated that the hydrogen-bonding modes (single and double hydrogen acceptor bonds) depend on temperature and/or coverage, which may in turn affect the weakening of the O-H bond, and hence the catalytic effects of trimethylamine. XPS also clearly detected a minority species, trimethylamine, datively bonded to the isolated silicon dangling bonds (a few 1/100th of a monolayer). This species is prone to breaking, and a detailed analysis of the reaction products was made. The reactivity of the electrically active isolated silicon dangling bonds with the amine may impact the Fermi-level position in the gap. © 2022 American Chemical Society

Fuel cells recombine water from H2 and O2 thereby can power, for example, cars or houses with no direct carbon emission. In anion-exchange membrane fuel cells (AEMFCs), to reach high power densities, operating at high pH is an alternative to using large volumes of noble metals catalysts at the cathode, where the oxygen-reduction reaction occurs. However, the sluggish kinetics of the hydrogen-oxidation reaction (HOR) hinders upscaling despite promising catalysts. Here, the authors observe an unexpected ingress of B into Pd nanocatalysts synthesized by wet-chemistry, gaining control over this B-doping, and report on its influence on the HOR activity in alkaline conditions. They rationalize their findings using ab initio calculations of both H- and OH-adsorption on B-doped Pd. Using this “impurity engineering” approach, they thus design Pt-free catalysts as required in electrochemical energy conversion devices, for example, next generations of AEMFCs, that satisfy the economic and environmental constraints, that is, reasonable operating costs and long-term stability, to enable the “hydrogen economy.”. © 2022 The Authors. Advanced Materials published by Wiley-VCH GmbH.

Atom probe tomography (APT) analysis is being actively used to provide near-atomic-scale information on the composition of complex materials in three-dimensions. In recent years, there has been a surge of interest in the technique to investigate the distribution of hydrogen in metals. However, the presence of hydrogen in the analysis of almost all specimens from nearly all material systems has caused numerous debates as to its origins and impact on the quantitativeness of the measurement. It is often perceived that most H arises from residual gas ionization, therefore affecting primarily materials with a relatively low evaporation field. In this work, we perform systematic investigations to identify the origin of H residuals in APT experiments by combining density-functional theory (DFT) calculations and APT measurements on an alkali and a noble metal, namely Na and Pt, respectively. We report that no H residual is found in Na metal samples, but in Pt, which has a higher evaporation field, a relatively high signal of H is detected. These results contradict the hypothesis of the H signal being due to direct ionization of residual H2 without much interaction with the specimen's surface. Based on DFT, we demonstrate that alkali metals are thermodynamically less likely to be subject to H contamination under APT-operating conditions compared to transition or noble metals. These insights indicate that the detected H-signal is not only from ionization of residual gaseous H2 alone, but is strongly influenced by material-specific physical properties. The origin of H residuals is elucidated by considering different conditions encountered during APT experiments, specifically, specimen-preparation, transportation, and APT-operating conditions by taking thermodynamic and kinetic aspects into account. © 2022 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft.

Electrocatalytic oxidation of glycerol (GOR) as the anode reaction in water electrolysis facilitates the production of hydrogen at the cathode at a substantially lower cell voltage compared with the oxygen evolution reaction. It simultaneously provides the basis for the production of value-added compounds at the anode. We investigate earth-abundant transition-metal oxide nanoparticles (Fe, Ni, Mn, Co) embedded in multiwalled carbon nanotubes as GOR catalysts. Out of the four investigated composites, the Ni-based catalyst exhibits the highest catalytic activity toward the GOR according to rotating disk electrode voltammetry, reaching a current density of 10 mA cm–2 already at 1.31 V vs RHE, a potential below the formation of Ni3+. Chronoamperometry conducted in a flow-through cell followed by HPLC analysis is used to identify and quantify the GOR products over time, revealing that the applied potential, electrolyte concentration, and duration of the experiment impact strongly the composition of the products’ mixture. Upon optimization, the GOR is directed toward oxalate production. Moreover, oxalate is not further converted and hence accumulates as a major organic product under the chosen conditions in a concentration ratio of 60:1 with acetate as a minor product after 48 h electrolysis in 7 M KOH, which represents a promising route for the synthesis of this highly valued product. © 2022 American Chemical Society

In this work, a novel in situ auto-reduction strategy was developed to encapsulate uniformly dispersed Pd clusters/nanoparticles in MIL-125-NH2. It is demonstrated that the amino groups in MIL-125-NH2 can react with formaldehyde to form novel reducing groups (-NH[sbnd]CH2OH), which can in situ auto-reduce the encapsulated Pd2+ ions to metallic Pd clusters/nanoparticles. As no additional reductants are required, the strategy limits the aggregation and migration of Pd clusters and the formation of large Pd nanoparticles via controlling the amount of Pd2+ precursor. When applied as catalysts in the hydrogenation of phenol in the aqueous phase, the obtained Pd(1.5)/MIL-125-NH-CH2OH catalyst with highly dispersed Pd clusters/nanoparticles with the size of around 2 nm exhibited 100% of phenol conversion and 100% of cyclohexanone selectivity at 70 °C after 5 h, as well as remarkable reusability for at least five cycles due to the large MOF surface area, the highly dispersed Pd clusters/nanoparticles and their excellent stability within the MIL-125-NH-CH2OH framework. © 2021

The development of noble-metal-free electrocatalysts is regarded as a key factor for realizing industrial-scale hydrogen production powered by renewable energy sources. Inspired by nature, which uses Fe-and Ni-containing enzymes for efficient hydrogen generation, Fe/Ni-containing chalcogenides, such as oxides and sulfides, received increasing attention as promising electrocatalysts to produce hydrogen. We herein present a novel synthetic procedure for mixed Fe/Ni (oxy)sulfide materials by the controlled (partial) sulfidation of NiFe2O4 (NFO) nanoparticles in H2S-containing atmospheres. The variation in H2S concentration and the temperature allows for a precise control of stoichiometry and phase composition. The obtained sulfidized materials (NFS) catalyze the hydrogen evolution reaction (HER) with increased activity in comparison to NFO, up to −10 and −100 mA cm−2 at an overpotential of approx. 250 and 450 mV, respectively. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.

Numerous metallurgical and materials science applications depend on quantitative atomic-scale characterizations of environmentally-sensitive materials and their transient states. Studying the effect upon materials subjected to thermochemical treatments in specific gaseous atmospheres is of central importance for specifically studying a material’s resistance to certain oxidative or hydrogen environments. It is also important for investigating catalytic materials, direct reduction of an oxide, particular surface science reactions or nanoparticle fabrication routes. This manuscript realizes such experimental protocols upon a thermochemical reaction chamber called the "Reacthub" and allows for transferring treated materials under cryogenic & ultrahigh vacuum (UHV) workflow conditions for characterisation by either atom probe or scanning Xe+/electron microscopies. Two examples are discussed in the present study. One protocol was in the deuterium gas charging (25 kPa D2 at 200°C) of a high-manganese twinning-induced-plasticity (TWIP) steel and characterization of the ingress and trapping of hydrogen at various features (grain boundaries in particular) in efforts to relate this to the steel’s hydrogen embrittlement susceptibility. Deuterium was successfully detected after gas charging but most contrast originated from the complex ion FeOD+ signal and the feature may be an artefact. The second example considered the direct deuterium reduction (5 kPa D2 at 700°C) of a single crystal wüstite (FeO) sample, demonstrating that under a standard thermochemical treatment causes rapid reduction upon the nanoscale. In each case, further studies are required for complete confidence about these phenomena, but these experiments successfully demonstrate that how an ex-situ thermochemical treatment can be realised that captures environmentally-sensitive transient states that can be analysed by atomic-scale by atom probe microscope. © 2022 Khanchandani et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Non-classical alternatives to the silver contact and the Formox processes comprise the thermal non-oxidative dehydrogenation of methanol, for which new catalysts are needed to achieve high formaldehyde selectivity at high conversion at temperatures below 600 °C. The electro- or photocatalytic conversion of methanol to formaldehyde is not applied either industrially but is attractive because of mild reaction conditions and high formaldehyde selectivities. Novel gas-phase approaches yielding (anhydrous) formaldehyde are presented describing lab-scale setups and the challenges for up-scaling. © 2022 The Authors. Chemie Ingenieur Technik published by Wiley-VCH GmbH.

Gas diffusion electrodes (GDE) obtained by sputtering metal films on polytetrafluoroethylene (PTFE) membranes are among the most performant electrodes used to electrochemically reduce CO2. The present work reveals several essential aspects for fabricating performant PTFE-based gas diffusion electrodes (GDEs) for CO2 electroreduction (CO2R). We show that adding an additive layer (a mixture of carbon and Nafion™ or Nafion™ only) is required for stabilizing the metal catalyst film (Cu), deposited via sputtering on the PTFE membrane, during the CO2R experiments. We found that the PTFE membrane thickness used in the GDE fabrication plays an essential role in electrode performance. The quantification of the products formed during the CO2R conducted in a flow-cell electrolyzer revealed that on thinner membranes, CO2R is the dominant process while on thicker ones, the H2 formation is promoted. Thus, the PTFE membrane influences the CO2 transport to the catalyst layer and can be used to promote the CO2R while maintaining a minimum H2 production. © 2021 The Authors. ChemElectroChem published by Wiley-VCH GmbH

Mitigating high energy costs related to sustainable H2 production via water electrolysis is important to make this process commercially viable. Possible approaches are the investigation of low-cost, highly active oxygen evolution reaction (OER) catalysts and the exploration of alternative anode reactions, such as the electrocatalytic isopropanol oxidation reaction (iPOR) or the glycerol oxidation reaction (GOR), offering the possibility of simultaneously lowering the anodic overpotential and generating value-added products. A suitable class of catalysts are non-noble metal-based perovskites with the general formula ABO3, featuring rare-earth metal cations at the A- and transition metals at the B-site. We synthesised a series of LaFe1-xCoxO3 materials with x=0–0.70 by automated co-precipitation at constant pH and subsequent calcination at 800 °C. X-ray diffraction studies revealed that the phase purity was preserved in samples with x≤0.3. The activity towards the OER, iPOR, and GOR was investigated by rotating disk electrode voltammetry, showing a relation between structure and metal composition with the activity trends observed for the three reactions. Additionally, GOR product analysis via high-performance liquid chromatography (HPLC) was conducted after 24 and 48 h electrolysis in a circular flow-through cell setup, pointing out a trade-off between activity and selectivity. © 2022 The Authors. ChemElectroChem published by Wiley-VCH GmbH

Iron- and steelmaking cause ∼7% of the global CO2 emissions, due to the use of carbon for the reduction of iron ores. Replacing carbon by hydrogen as the reductant offers a pathway to massively reduce these emissions. However, the production of hydrogen using renewable energy will remain as one of the bottlenecks at least during the next two decades, because making the gigantic annual crude steel production of 1.8 billion tons sustainable requires a minimum stoichiometric amount of ∼97 million tons of green hydrogen per year. Another fundamental aspect to render the ironmaking sector more sustainable lies in an optimal utilization of green hydrogen and energy, thus reducing efforts for costly in-process hydrogen recycling. We therefore demonstrate here how the efficiency in hydrogen and energy consumption during iron ore reduction can be dramatically improved by the knowledge-based combination of two technologies: partially reducing the ore at low temperature via solid-state direct reduction (DR) to a kinetically defined degree, and subsequently melting and completely transforming it to iron under a reducing plasma (i.e. via hydrogen plasma reduction, HPR). Results suggest that an optimal transition point between these two technologies occurs where their efficiency in hydrogen utilization is equal. We found that the reduction of hematite through magnetite into wüstite via DR is clean and efficient, but it gets sluggish and inefficient when iron forms at the outermost layers of the iron ore pellets. Conversely, HPR starts violent and unstable with arc delocalization, but proceeds smoothly and efficiently when processing semi-reduced oxides, an effect which might be related to the material's high electrical conductivity. We performed hybrid reduction experiments by partially reducing hematite pellets via DR at 700 °C to 38% global reduction (using a standard thermogravimetry system) and subsequently transferring them to HPR, conducted with a lean gas mixture of Ar-10%H2 in an arc-melting furnace, to achieve full conversion into liquid iron. This hybrid approach allows to exploit the specific characteristics and kinetically favourable regimes of both technologies, while simultaneously showing the potential to keep the consumption of energy and hydrogen low and improve both, process stability and furnace longevity by limiting its overexposure to plasma radiation. © 2022 Elsevier Ltd

CO2 methanation using nickel-based catalysts has attracted large interest as a promising power-to-gas route. Ni nanoparticles supported on nitrogen-doped CNTs with Ni loadings in the range from 10 wt% to 50 wt% were synthesized by impregnation, calcination and reduction and characterized by elemental analysis, X-ray powder diffraction, H2 temperature-programmed reduction, CO pulse chemisorption and transmission electron microscopy. The Ni/NCNT catalysts were highly active in CO2 methanation at atmospheric pressure, reaching over 50% CO2 conversion and over 95% CH4 selectivity at 340 °C and a GHSV of 50,000 mL g−1 h−1 under kinetically controlled conditions. The small Ni particle sizes below 10 nm despite the high Ni loading is ascribed to the efficient anchoring on the N-doped CNTs. The optimum loading of 30 wt%–40 wt% Ni was found to result in the highest Ni surface area, the highest degree of conversion and the highest selectivity to methane. A constant TOF of 0.3 s−1 was obtained indicating similar catalytic properties of the Ni nanoparticles in the range from 10 wt% to 50 wt% Ni loading. Long-term experiments showed that the Ni/NCNT catalyst with 30 wt% Ni was highly stable for 100 h time on stream. © 2020 Science Press

A step in the direction of the real-life application of fuel cells (FCs) has been realized through the fabrication of a promising proton conductive membrane comprising a perfluorosulfonic-acid ionomer and nitrogen-rich poly[2,2′-(4,4′-bipyridine)-5,5′-bibenzimidazole] (BiPyPBI). The BiPyPBI-perfluorosulfonic acid membranes displayed remarkable oxidative and mechanical stabilities with significant proton conduction over wide ranges of temperatures (40 to 140 °C) and humidities (30 to 90% RH). A 0.5 molar BiPyPBI feed ratio increased the proton conduction of perfluorosulfonic acid by 2.6- and 1.5-fold at 40 and 80 °C, respectively, due to the enhancement in the ion-exchange capacity (1.9 mmol/g, which was twofold higher than that of bare Nafion). The protonic conductivity reached 0.171 S/cm at 140 °C. Using a BiPyPBI feed increased the stability of the Nafion membrane, corresponding to a 3.5-fold increase in the mechanical stress (9.6 MPa) and a 2.2-fold decrease in the elongation at break. In addition, the oxidation stability of the Nafion membrane increased by 26%. The measured activation energy suggested that the presence of BiPyPBI created an easier proton transport pathway (by the Grotthuss mechanism) because of a stronger hydrogen-bonding network than in bare Nafion. Compared to the power density of a perfluorosulfonic-based MEA, the power density of the BiPyPBI-perfluorosulfonic-based membrane electrode assembly (MEA) at 140 °C increased by approximately 20-fold to 175 mW cm-1 at 30% RH and by approximately 5-fold to 201 mW cm-1 at 90% RH. Impedance spectra confirmed the improvement of the FC performance of the BiPyPBI-perfluorosulfonic-based MEA, indicating enhanced charge transfer. After 10,000 cycles of relative humidity stress testing, the BiPyPBI-perfluorosulfonic-based MEA showed a power density of 146 mW cm-1 (corresponding to a 16% loss in the initial power density measured at 30% RH). The MEA lost only 26% of its initial power density upon relative humidity stress cycling. © 2021 American Chemical Society.

Photocatalytic oxidation of alcohols has received more and more attention in recent years following the numerous studies on the degradation of pollutants, hydrogen evolution, and CO2 reduction by photocatalysis. Instead of the total oxidation of organics in the degradation process, the photo-oxidation of alcohols aims at the selective conversion of alcohols to produce carbonyl/acid compounds. Promising results have been achieved in designing the catalysts and reaction system, as well as in the mechanistic investigations in the past few years. This review summarizes the state-of-the-art progress in the photo-oxidation of alcohols, including the development of photocatalysts and cocatalysts, reaction conditions including the solvent and the atmosphere, and the exploration of mechanisms with scavengers experiment, electron paramagnetic resonance (EPR) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The challenges and outlook for the further research in this field are also discussed. © 2021 Science Press

Metastable austenitic steels react to plastic deformation with a thermally and/or mechan-ically induced martensitic phase transformation. The martensitic transformation to α’‐martensite can take place directly or indirectly via the intermediate stage of ε‐martensite from the single‐phase austenite. This effect is influenced by the stacking fault energy (SFE) of austenitic steels. An SFE < 20 mJ/m2 is known to promote indirect conversion, while an SFE > 20 mJ/m2 promotes the direct conversion of austenite into α’‐martensite. This relationship has thus far not been considered in relation to the hydrogen environment embrittlement (HEE) of metastable austenitic CrNi steels. To gain new insights into HEE under consideration of the SFE and martensite formation of metastable CrNi steels, tensile tests were carried out in this study at room temperature in an air environment and in a hydrogen gas atmosphere with a pressure of p = 10 MPa. These tests were conducted on a conventionally produced alloy AISI 304L and a laboratory‐scale modification of this alloy. In terms of metal physics, the steels under consideration differed in the value of the experimentally deter-mined SFE. The SFE of the AISI 304L was 22.7 ± 0.8 mJ/m2 and the SFE of the 304 mod alloy was 18.7 ± 0.4 mJ/m2. The tensile specimens tested in air revealed a direct γ→α’ conversion for AISI 304L and an indirect γ→ε→α’ conversion for 304mod. From the results it could be deduced that the indirect phase transformation is responsible for a significant increase in the content of deformation‐induced α’‐martensite due to a reduction of the SFE value below 20 mJ/m2 in hydrogen gas atmosphere. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

The antagonism between strength and resistance to hydrogen embrittlement in metallic materials is an intrinsic obstacle to the design of lightweight yet reliable structural components operated in hydrogen-containing environments. Economical and scalable microstructural solutions to this challenge must be found. Here, we introduce a counterintuitive strategy to exploit the typically undesired chemical heterogeneity within the material’s microstructure that enables local enhancement of crack resistance and local hydrogen trapping. We use this approach in a manganese-containing high-strength steel and produce a high dispersion of manganese-rich zones within the microstructure. These solute-rich buffer regions allow for local micro-tuning of the phase stability, arresting hydrogen-induced microcracks and thus interrupting the percolation of hydrogen-assisted damage. This results in a superior hydrogen embrittlement resistance (better by a factor of two) without sacrificing the material’s strength and ductility. The strategy of exploiting chemical heterogeneities, rather than avoiding them, broadens the horizon for microstructure engineering via advanced thermomechanical processing. © 2021, The Author(s).

Removing artificial bands from the back side of surface slabs with pseudohydrogen atoms has become the method of choice to boost the convergence of density-functional theory (DFT) surface calculation with respect to slab thickness. In this paper we apply this approach to semipolar compound semiconductor surfaces, which have recently become attractive for device applications. We show that approaches employing saturation of dangling bonds by pseudohydrogen atoms alone are inadequate to properly passivate the surfaces, remove spurious surface states from the fundamental band gap, and achieve flat band conditions in the slab. We propose and successfully apply to technologically interesting semipolar wurtzite surfaces of III-N, III-V, and II-VI semiconductors a reconstruction-inspired passivation scheme that utilizes native anions to passivate cation dangling bonds and pseudohydrogen atoms to obey the electron counting rule and compensate for polarization-induced surface-bound charges. This scheme is generic and robust and can be straightforwardly implemented in DFT investigations of low-symmetry surfaces as well as in high-throughput and machine learning studies. © 2021 authors.

In this study, multi-wall carbon nanotubes (MWCNTs) were electrochemically modified with nitrogen and phosphorus species and employed as platform to immobilize pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH) for the fabrication of bioelectrodes for glucose detection. Depending on the upper potential limit used during the electrochemical modification of MWCNTs, the nature and amount of the nitrogen and phosphorus species incorporated in the carbon material surface can be selectively controlled. These species act as anchoring groups for the immobilization of the PQQ-GDH. The value of the upper potential limit used in the electrochemical modification influences the electron-transfer rate between the electrode and the enzyme. The performance of the bioelectrodes for glucose oxidation and detection is improved by the electrochemical modification conditions, leading to an increased sensitivity towards glucose oxidation from 39.2 to 53.6 mA gMWCNT−1 mM−1 in a linear range between 0.1 to 1.2 mM. This electrochemical modification is considered as an alternative for the preparation of highly sensitive glucose bioelectrodes. © 2021

Unraveling the atomistic and the electronic structure of solid-liquid interfaces is the key to the design of new materials for many important applications, from heterogeneous catalysis to battery technology. Density functional theory (DFT) calculations can, in principle, provide a reliable description of such interfaces, but the high computational costs severely restrict the accessible time and length scales. Here, we report machine learning-driven simulations of various interfaces between water and lithium manganese oxide (LixMn2O4), an important electrode material in lithium ion batteries and a catalyst for the oxygen evolution reaction. We employ a high-dimensional neural network potential to compute the energies and forces several orders of magnitude faster than DFT without loss in accuracy. In addition, a high-dimensional neural network for spin prediction is utilized to analyze the electronic structure of the manganese ions. Combining these methods, a series of interfaces is investigated by large-scale molecular dynamics. The simulations allow us to gain insights into a variety of properties, such as the dissociation of water molecules, proton transfer processes, and hydrogen bonds, as well as the geometric and electronic structure of the solid surfaces, including the manganese oxidation state distribution, Jahn-Teller distortions, and electron hopping. © 2021 Author(s).

A mononuclear oxoiron(iv) complex1-transbearing two equatorial sulfur ligations is synthesized and characterized as an active-site model of the elusive sulfur-ligated FeIVO intermediates in non-heme iron oxygenases. The introduction of sulfur ligands weakens the Fe-O bond and enhances the oxidative reactivity of the FeIVO unit with a diminished deuterium kinetic isotope effect, thereby providing a compelling rationale for nature's use of thecis-thiolate ligated oxoiron(iv) motif in key metabolic transformations. © The Royal Society of Chemistry 2021.

Metal-rich transition metal sulfides recently gained increasing attention as electrocatalysts for the hydrogen evolution reaction (HER), as they are capable to overcome major challenges faced by sulfide-rich metal catalysts such as limited conductivity and the necessity of nanostructuring. Herein, we present the synthesis, characterization and electrocatalytic investigation of ternary metal-rich sulfide composites FexCo9–xS8 as well as NiyCo9–yS8 (x = y = 0–4.5), which possess pentlandite-type structures. In this study, we show a stepwise alteration of the binary cobalt pentlandite Co9S8 and report on the replacement of cobalt with up to 4.5 equivalents of either iron or nickel. These altered pentlandite composites facilitate the proton reduction in acidic media at different temperatures. We furthermore show that the stoichiometric variation has a decisive influence on the electrochemical activation/deactivation behavior of the catalysts under reductive electrocatalytic conditions. Here, Co-deficient composites display an improved HER performance in contrast to Co9S8. Notably, Ni/Co compounds generally tend to show higher catalytic activities towards HER than their respective Fe/Co compounds. © 2021 Dalian Institute of Chemical Physics, the Chinese Academy of Sciences

Enzymatic hydrolysis of lignocellulosic biomass for biofuel production relies on complex multi-enzyme ensembles. Continuous and accurate measurement of the released key products is crucial in optimizing the industrial degradation process and also investigating the activity and interaction between the involved enzymes and the insoluble substrate. Amperometric biosensors have been applied to perform continuous cellobiose measurements during the enzymatic hydrolysis of pure cellulose powders. The oxygen-sensitive mediators used in these biosensors restricted their function under physiological or industrial conditions. Also, the combined measurements of the hydrolysis products cellobiose and glucose require a high selectivity of the biorecognition elements. We employed an [Os(2,2′-bipyridine)2Cl]Cl-modified polymer and cellobiose dehydrogenase to fabricate a cellobiose biosensor, which can accurately and specifically detect cellobiose even in the presence of oxygen and the other main product glucose. Additionally, a glucose biosensor was fabricated to simultaneously measure glucose produced from cellobiose by β-glucosidases. The cellobiose and glucose biosensors work at applied potentials of +0.25 and +0.45 V versus Ag|AgCl (3 M KCl), respectively, and can selectively detect their substrate. Both biosensors were used in combination to monitor the hydrolysis of pure cellulose of low crystallinity or industrial corncob samples. The obtained results correlate with the high-performance liquid chromatography pulsed amperometric detection analysis and demonstrate that neither oxygen nor the presence of redox-active compounds from the lignin fraction of the corncob interferes with the measurements. © 2021 The Authors. Published by American Chemical Society.

Diffusion of hydrogen bearing species in glasses plays a significant role in numerous applications in commercial as well as scientific domains. The investigation of diffusion of water in glasses at low temperatures led to experimental and analytical difficulties in the past. We present a new approach that lets us overcome these complications. Diffusion couples of An50Di50 glass (mol %, NBO/T = 0.67) were produced by coating anhydrous glass substrates with thin films of hydrated glass (~200 nm, ~2 wt% H2O) using pulsed laser deposition (PLD). Bonding the diffusant to the glass matrix of the thin film instead of using free water at the interface during experiments precludes other glass altering processes such as dissolution and precipitation. This allows us to confidently interpret the measured profiles to be a result of diffusion only. Nanoscale concentration profiles that result from diffusion at low temperatures on experimentally feasible time scales were measured with the Nuclear Resonance Reaction Analysis (NRRA, 1H(15N,αγ)12C). The non-destructive nature of NRRA enables us to observe and better understand the evolution of diffusion profiles with time within one sample. Evaluation of the sample quality by EPMA, SEM, optical microscopy, Rutherford backscattering spectroscopy (RBS), and NRRA was performed and confirmed the suitability of the samples for diffusion studies. Experiments at 1 atm in a box furnace and at 2 kbar in a CSPV (pressure medium = water) and an IHPV (pressure medium = Argon) prove that the diffusion couples can be used under various experimental conditions. We present diffusion profiles that were measured in experiments carried out in these devices and discuss the distinct features of each that result from different boundary conditions in the experiments. © 2020 Elsevier B.V.

Hydrogenases are bidirectional redox enzymes that catalyze hydrogen turnover in archaea, bacteria, and algae. While all types of hydrogenase show H2oxidation activity, [FeFe]-hydrogenases are excellent H2evolution catalysts as well. Their active site cofactor comprises a [4Fe-4S] cluster covalently linked to a diiron site equipped with carbon monoxide and cyanide ligands. The active site niche is connected with the solvent by two distinct proton transfer pathways. To analyze the catalytic mechanism of [FeFe]-hydrogenase, we employoperandoinfrared spectroscopy and infrared spectro-electrochemistry. Titrating the pH under H2oxidation or H2evolution conditions reveals the influence of site-selective protonation on the equilibrium of reduced cofactor states. Governed by pKadifferences across the active site niche and proton transfer pathways, we find that individual electrons are stabilized either at the [4Fe-4S] cluster (alkaline pH values) or at the diiron site (acidic pH values). This observation is discussed in the context of the complex interdependence of hydrogen turnover and bulk pH. © The Royal Society of Chemistry 2021.

The use of biomolecules as capping and reducing agents in the synthesis of metallic nanoparticles constitutes a promising framework to achieve desired functional properties with minimal toxicity. The system's complexity and the large number of variables involved represent a challenge for theoretical and experimental investigations aiming at devising precise synthesis protocols. In this work, we use L-asparagine (Asn), an amino acid building block of large biomolecular systems, to synthesise gold nanoparticles (AuNPs) in aqueous solution at controlled pH. The use of Asn offers a primary system that allows us to understand the role of biomolecules in synthesising metallic nanoparticles. Our results indicate that AuNPs synthesised in acidic (pH 6) and basic (pH 9) environments exhibit somewhat different morphologies.We investigate these AuNPs via Raman scattering experiments and classical molecular dynamics simulations of zwitterionic and anionic Asn states adsorbing on (111)-, (100)-, (110)-, and (311)-oriented gold surfaces. A combined analysis suggests that the underlying mechanism controlling AuNPs geometry correlates with amine's preferential adsorption over ammonium groups, enhanced upon increasing pH. Our simulations reveal that Asn (both zwitterionic and anionic) adsorption on gold (111) is essentially different from adsorption on more open surfaces. Water molecules strongly interact with the gold face-centred-cubic lattice and create traps, on the more open surfaces, that prevent the Asn from diffusing. These results indicate that pH is a relevant parameter in green-synthesis protocols with the capability to control the nanoparticle's geometry, and pave the way to computational studies exploring the effect of water monolayers on the adsorption of small molecules on wet gold surfaces. © 2021 The Author(s).

The present study describes an interesting and practical catalytic system that allows flexible conversion of lignin into aromatic or aliphatic hydrocarbons, depending on the hydrogen partial pressure. A combination of experiment and theory shows that the product distribution between aromatics and aliphatics can be simply tuned by controlling the availability of hydrogen on the catalyst surface. Noticeably, these pathways lead to almost complete oxygen removal from lignin biomass, yielding high-quality hydrocarbons. Thus, hydrogen–lignin co-refining by using this catalytic system provides high flexibility in hydrogen storage/consumption towards meeting different regional and temporal demands. © 2020 The Authors. ChemSusChem published by Wiley-VCH GmbH

[FeFe]-hydrogenases are efficient H2-catalysts, yet upon contact with dioxygen their catalytic cofactor (H-cluster) is irreversibly inactivated. Here, we combine X-ray crystallography, rational protein design, direct electrochemistry, and Fourier-transform infrared spectroscopy to describe a protein morphing mechanism that controls the reversible transition between the catalytic Hox-state and the inactive but oxygen-resistant Hinact-state in [FeFe]-hydrogenase CbA5H of Clostridium beijerinckii. The X-ray structure of air-exposed CbA5H reveals that a conserved cysteine residue in the local environment of the active site (H-cluster) directly coordinates the substrate-binding site, providing a safety cap that prevents O2-binding and consequently, cofactor degradation. This protection mechanism depends on three non-conserved amino acids situated approximately 13 Å away from the H-cluster, demonstrating that the 1st coordination sphere chemistry of the H-cluster can be remote-controlled by distant residues. © 2021, The Author(s).

Selective water oxidation to hydrogen peroxide has emerged as an economically attractive replacement for oxygen in electrochemical hydrogen production by water splitting. Here, boron-doped diamond (BDD) is shown to be a promising anode material for anodic H2O2 formation. Faradaic efficiencies of up to 31.7% at 2.90 V versus the reference hydrogen electrode and a current density of 39.8 mA cm-2 were observed, corresponding to a H2O2 production rate of 3.93 μmol min-1 cm-2. A techno-economic evaluation based on the experimentally obtained values demonstrates that the corresponding levelized cost of hydrogen (LCH) is significant ($62.0 kg-1). Particularly, the current market price of BDD limits its implementation as a selective water oxidation anode for H2O2 generation. The sensitivity analysis however suggests that the LCH can be significantly improved by either decreasing the anode cost or increasing the current density. Both approaches are in fact feasible to allow for cost-effective electrochemical H2 production and even competition with H2 obtained from steam methane reforming. This study will guide ongoing research efforts toward BDD development and implementation of selective water oxidation to hydrogen peroxide. © 2021 The Authors. Published by American Chemical Society.

Discerning the influence of electrochemical reactions on the electrode microenvironment is an unavoidable topic for electrochemical reactions that involve the production of OH− and the consumption of water. That is particularly true for the carbon dioxide reduction reaction (CO2RR), which together with the competing hydrogen evolution reaction (HER) exert changes in the local OH− and H2O activity that in turn can possibly affect activity, stability, and selectivity of the CO2RR. We determine the local OH− and H2O activity in close proximity to a CO2-converting Ag-based gas diffusion electrode (GDE) with product analysis using gas chromatography. A Pt nanosensor is positioned in the vicinity of the working GDE using shear-force-based scanning electrochemical microscopy (SECM) approach curves, which allows monitoring changes invoked by reactions proceeding within an otherwise inaccessible porous GDE by potentiodynamic measurements at the Pt-tip nanosensor. We show that high turnover HER/CO2RR at a GDE lead to modulations of the alkalinity of the local electrolyte, that resemble a 16 m KOH solution, variations that are in turn linked to the reaction selectivity. © 2021 The Authors. Published by Wiley-VCH GmbH

Hydrogen production is a key driver for sustainable and clean fuels used to generate electricity, which can be achieved through electrochemical splitting of water in alkaline solutions. However, the hydrogen evolution reaction (HER) is kinetically sluggish in alkaline media. Therefore, it has become imperative to develop inexpensive and highly efficient electrocatalysts that can replace the existing expensive and scarce noble-metal-based catalysts. Herein, we report on the rational design of nonprecious heterostructured electrocatalysts comprising a highly conductive face-centered cubic nickel metal, a nickel sulfide (NiS) phase, and a reduced graphene oxide (rGO) doped with phosphorous (P), sulfur (S), and nitrogen (N) in one ordered heteromaterial named Ni/NiS/P,N,S-rGO. The Ni/NiS/P,N,S-rGO electrode shows the best performance toward HER in 1.0 M KOH media among all materials tested with an overpotential of 155 mV at 10.0 mA cm-2 and a Tafel slope of 135 mV dec-1. The performance is comparable to the herein used Pt/C-20% benchmark catalyst examined under the same experimental conditions. The chronoamperometry and chronopotentiometry measurements have reflected the high durability of the Ni/NiS/P,N,S-rGO electrode for technological applications. At the same time, the current catalyst showed a high robustness and structure retention after long-term HER performance, which is reflected by SEM, XRD, and XPS measurements. ©

While hydrogen plays an ever-increasing role in modern society, nature has utilized hydrogen since a very long time as an energy carrier and storage molecule. Among the enzymatic systems that metabolise hydrogen, [FeFe]-hydrogenases are one of the most powerful systems to perform this conversion. In this light, we will herein present an overview on developments in [FeFe]-hydrogenase research with a strong focus on synthetic mimics and their application within the native enzymatic environment. This review spans from the biological assembly of the natural enzyme and the highly controversial discussed mechanism for the hydrogen generation to the synthesis of multiple mimic platforms as well as their electrochemical behaviour. © The Royal Society of Chemistry.

The double layer at the solid/electrolyte interface is a key concept in electrochemistry. Here, we present an experimental study combined with simulations, which provides a molecular picture of the double-layer formation under applied voltage. By THz spectroscopy we are able to follow the stripping away of the cation/anion hydration shells for an NaCl electrolyte at the Au surface when decreasing/increasing the bias potential. While Na+ is attracted toward the electrode at the smallest applied negative potentials, stripping of the Cl2 hydration shell is observed only at higher potential values. These phenomena are directly measured by THz spectroscopy with ultrabright synchrotron light as a source and rationalized by accompanying molecular dynamics simulations and electronic-structure calculations. © 2021 National Academy of Sciences. All rights reserved.

We report the fabrication and characterization of molybdenum (Mo)-doped ZnV2O6/reduced graphene oxide (rGO) composite and its use as photoanode for photoelectrochemical (PEC) hydrogen production. Compared to pure ZnV2O6, Mo ions act as electron donor in the ZnV2O6:Mo lattice increasing charge carrier concentration and subsequently mobility in the bulk by the polaron transport. We measured the hole transfer efficiency for the pure and Mo-doped ZnV2O6 electrodes and revealing a substantial increase from 16 to 25%. The mechanism of enhanced photoactivity of Mo-doped ZnV2O6 was studied by density functional theory calculations. Moreover, electrochemical impedance spectroscopy measurements show that graphene modification improves carrier separation and transfer across the electrode/electrolyte interface. Therefore, the combination of the two strategies triggers a synergistic enhancement in PEC performance in terms of incident photon-to-current efficiency, which is 17% at 370 nm, being 4.5- and 3.6-times greater than those of pristine ZnV2O6 and ZnV2O6:Mo photoanodes, respectively. With photocurrent onset potentials of 0.6 V and photocurrent densities of 2.07 mA/cm2 at 1.23 V vs. RHE, ZnV2O6:Mo/rGO photoanodes are of interest for the design of high performance PEC visible-light-induced water-splitting devices. © 2021

Hydrogen embrittlement in 304L austenitic stainless steel fabricated by laser powder-bed-fusion (LPBF) was investigated and compared to conventionally produced 304L samples with two different processing histories; casting plus annealing (CA) and CA plus thermomechanical treatment (CA-TMT). Interestingly, no significant difference in the amount of deformation-induced α′ martensite between the LPBF and CA-TMT samples was observed, suggesting that the solidification substructure in the LPBF sample enhanced the strength without promoting the harmful hydrogen embrittlement effect. These results are discussed in terms of the chemical inhomogeneity, hydrogen-assisted cracking behavior, and hydrogen diffusion and trapping in the present 304L samples. © 2020

Steel is the most important material class in terms of volume and environmental impact. While it is a sustainability enabler, for instance through lightweight design, magnetic devices, and efficient turbines, its primary production is not. Iron is reduced from ores by carbon, causing 30% of the global CO2 emissions in manufacturing, qualifying it as the largest single industrial greenhouse gas emission source. Hydrogen is thus attractive as alternative reductant. Although this reaction has been studied for decades, its kinetics is not well understood, particularly during the wüstite reduction step which is much slower than hematite reduction. Some rate-limiting factors of this reaction are determined by the microstructure and local chemistry of the ores. Here, we report on a multi-scale structure and composition analysis of iron reduced from hematite with pure H2, reaching down to near-atomic scale. During reduction a complex pore- and microstructure evolves, due to oxygen loss and non-volume conserving phase transformations. The microstructure after reduction is an aggregate of nearly pure iron crystals, containing inherited and acquired pores and cracks. We observe several types of lattice defects that accelerate mass transport as well as several chemical impurities (Na, Mg, Ti, V) within the Fe in the form of oxide islands that were not reduced. With this study, we aim to open the perspective in the field of carbon-neutral iron production from macroscopic processing towards better understanding of the underlying microscopic transport and reduction mechanisms and kinetics. © 2021

Recently, efforts to realize methanol- and hydrogen-based economies coupled with enzymatic machineries e.g., via electrochemical conversion of CO2 and H2O, accelerated. However, major obstacles still need to be overcome to enable application of such methods in real life. In a nutshell, these are the establishment of (1) a scalable sustainable production of renewable hydrogen from water, (2) the energy-efficient production of methanol from carbon dioxide, and (3) low-temperature hydrogen evolution from small C1 molecules like methanol. In this perspective article, we will spread light on the possibilities to pave the way for near-room-temperature hydrogen evolution using aqueous (aq.) methanol by shuttling hydrogen and electrons via chemoenzymatic pathways using electrocatalytic systems. © 2021 The Author(s)

Iron- and steelmaking is the largest single industrial CO2 emitter, accounting for 6.5% of all CO2 emissions on the planet. This fact challenges the current technologies to achieve carbon-lean steel production and to align with the requirement of a drastic reduction of 80% in all CO2 emissions by around 2050. Thus, alternative reduction technologies have to be implemented for extracting iron from its ores. The hydrogen-based direct reduction has been explored as a sustainable route to mitigate CO2 emissions, where the reduction kinetics of the intermediate oxide product FexO (wüstite) into iron is the rate-limiting step of the process. The total reaction has an endothermic net energy balance. Reduction based on a hydrogen plasma may offer an attractive alternative. Here, we present a study about the reduction of hematite using hydrogen plasma. The evolution of both, chemical composition and phase transformations was investigated in several intermediate states. We found that hematite reduction kinetics depends on the balance between the initial input mass and the arc power. For an optimized input mass-arc power ratio, complete reduction was obtained within 15 min of exposure to the hydrogen plasma. In such a process, the wüstite reduction is also the rate-limiting step towards complete reduction. Nonetheless, the reduction reaction is exothermic, and its rates are comparable with those found in hydrogen-based direct reduction. Micro- and nanoscale chemical and microstructure analysis revealed that the gangue elements partition to the remaining oxide regions, probed by energy dispersive spectroscopy (EDS) and atom probe tomography (APT). Si-enrichment was observed in the interdendritic fayalite domains, at the wüstite/iron hetero-interfaces and in the oxide particles inside iron. With proceeding reduction, however, such elements are gradually removed from the samples so that the final iron product is nearly free of gangue-related impurities. Our findings provide microstructural and atomic-scale insights into the composition and phase transformations occurring during iron ore reduction by hydrogen plasma, propelling better understanding of the underlying thermodynamics and kinetic barriers of this essential process. © 2021

Traditionally, bandgap materials are a prerequisite to photocatalysis since they can harness a reasonable range of the solar spectrum. However, the high impedance across the bandgap and the low concentration of intrinsic charge carriers have limited their energy conversion. By contrast, metallic nanoparticles possess a sea of free electrons that can effectively promote the transition to the excited state for reactions. Here, an atomic layer of a bimetallic concoction of silver–gold shells is precisely fabricated onto an Au core via a sonochemical dispersion approach to form a core–shell of Au–Ag that exploits the wide availability of excited states of Ag while maintaining an efficient localized surface plasmon resonance (LSPR) of Au. Catalytic results demonstrate that this mix of Ag and Au can convert solar energy to hydrogen at high efficiency with an increase of 112.5% at an optimized potential of −0.5 V when compared to light-off conditions under the electrochemical LSPR. This outperforms the commercial Pt catalysts by 62.1% with a hydrogen production rate of 1870 µmol g−1 h−1 at room temperature. This study opens a new route for tuning the range of light capture of hydrogen evolution reaction catalysts using fabricated core–shell material through the combination of LSPR with electrochemical means. © 2021 Wiley-VCH GmbH

Pinning-type magnets with high coercivity at high temperatures are at the core of thriving clean-energy technologies. Among these, Sm2Co17-based magnets are excellent candidates owing to their high-temperature stability. However, despite intensive efforts to optimize the intragranular microstructure, the coercivity currently only reaches 20–30% of the theoretical limits. Here, the roles of the grain-interior nanostructure and the grain boundaries in controlling coercivity are disentangled by an emerging magnetoelectric approach. Through hydrogen charging/discharging by applying voltages of only ≈1 V, the coercivity is reversibly tuned by an unprecedented value of ≈1.3 T. In situ magneto-structural characterization and atomic-scale tracking of hydrogen atoms reveal that the segregation of hydrogen atoms at the grain boundaries, rather than the change of the crystal structure, dominates the reversible and substantial change of coercivity. Hydrogen reduces the local magnetocrystalline anisotropy and facilitates the magnetization reversal starting from the grain boundaries. This study opens a way to achieve the giant magnetoelectric effect in permanent magnets by engineering grain boundaries with hydrogen atoms. Furthermore, it reveals the so far neglected critical role of grain boundaries in the conventional magnetization-switching paradigm of pinning-type magnets, suggesting a critical reconsideration of engineering strategies to overcome the coercivity limits. © 2020 The Authors. Advanced Materials published by Wiley-VCH GmbH

By photodeposition of CrOxon SrTiO3-based semiconductors doped with aliovalent Mg(II) and functionalized with Ni/NiOxcatalytic nanoparticles (economically significantly more viable than commonly used Rh catalysts), an increase in apparent quantum yield (AQYs) from ∼10 to 26% in overall water splitting was obtained. More importantly, deposition of CrOxalso significantly enhances the stability of Ni/NiO nanoparticles in the production of hydrogen, allowing sustained operation, even in intermittent cycles of illumination.In situelemental analysis of the water constituents during or after photocatalysis by inductively coupled plasma mass spectrometry/optical emission spectrometry shows that after CrOxdeposition, dissolution of Ni ions from Ni/NiOx-Mg:SrTiO3is significantly suppressed, in agreement with the stabilizing effect observed, when both Mg dopant and CrOxare present. State-of-the-art electron microscopy and energy-dispersive X-ray spectroscopy (EDX) and electron energy-loss spectroscopy (EELS) analyses demonstrate that upon preparation, CrOxis photodeposited in the vicinity of several, but not all, Ni/NiOxparticles. This implies the formation of a Ni-Cr mixed metal oxide, which is highly effective in water reduction. Inhomogeneities in the interfacial contact, evident from differences in contact angles between Ni/NiOxparticles and the Mg:SrTiO3semiconductor, likely affect the probability of reduction of Cr(VI) species during synthesis by photodeposition, explaining the observed inhomogeneity in the spatial CrOxdistribution. Furthermore, by comparison with undoped SrTiO3, Mg-doping appears essential to provide such favorable interfacial contact and to establish the beneficial effect of CrOx. This study suggests that the performance of semiconductors can be significantly improved if inhomogeneities in interfacial contact between semiconductors and highly effective catalytic nanoparticles can be resolved by (surface) doping and improved synthesis protocols. © 2021 The Authors. Published by American Chemical Society

Despite outstanding accomplishments in catalyst discovery, finding new, more efficient, environmentally neutral, and noble metal-free catalysts remains challenging and unsolved. Recently, complex solid solutions consisting of at least five different elements and often named as high-entropy alloys have emerged as a new class of electrocatalysts for a variety of reactions. The multicomponent combinations of elements facilitate tuning of active sites and catalytic properties. Predicting optimal catalyst composition remains difficult, making testing of a very high number of them indispensable. We present the high-throughput screening of the electrochemical activity of thin film material libraries prepared by combinatorial co-sputtering of metals which are commonly used in catalysis (Pd, Cu, Ni) combined with metals which are not commonly used in catalysis (Ti, Hf, Zr). Introducing unusual elements in the search space allows discovery of catalytic activity for hitherto unknown compositions. Material libraries with very similar composition spreads can show different activities vs. composition trends for different reactions. In order to address the inherent challenge of the huge combinatorial material space and the inability to predict active electrocatalyst compositions, we developed a high-throughput process based on co-sputtered material libraries, and performed high-throughput characterization using energy dispersive X-ray spectroscopy (EDS), scanning transmission electron microscopy (SEM), X-ray diffraction (XRD) and conductivity measurements followed by electrochemical screening by means of a scanning droplet cell. The results show surprising material compositions with increased activity for the oxygen reduction reaction and the hydrogen evolution reaction. Such data are important input data for future data-driven materials prediction. [Figure not available: see fulltext.] © 2021, The Author(s).

Hydrogen spillover is the phenomenon where a hydrogen atom, generated from the dissociative chemisorption of dihydrogen on the surface of a metal species, migrates from the metal to the catalytic support. This phenomenon is regarded as a promising avenue for hydrogen storage, yet the atomic mechanism for how the hydrogen atom can be transferred to the support has remained controversial for decades. As a result, the development of catalytic support for such a purpose is only limited to typical reducible oxide materials. Herein, by using a combination of in situ spectroscopic and imaging technique, we are able to visualize and observe the atomic pathway for which hydrogen travels via a frustrated Lewis pair that has been constructed on a nonreducible metal oxide. The interchangeable status between the hydrogen, proton, and hydride is carefully characterized and demonstrated. It is envisaged that this study has opened up new design criteria for hydrogen storage material. © 2021 American Chemical Society.

Electrochemical oxidation of biomass substrates to valuable bio-chemicals is highly attractive. However, the design of efficient, selective, stable, and inexpensive electrocatalysts remains challenging. Here it is reported how a 3D highly ordered mesoporous Co3O4/nickel foam (om-Co3O4/NF) electrode fulfils those criteria in the electrochemical oxidation of 5-hydroxymethylfurfural (HMF) to value-added 2,5-furandicarboxylic acid (FDCA). Full conversion of HMF and an FDCA yield of >99.8 % are achieved with a faradaic efficiency close to 100 % at a potential of 1.457 V vs. reversible hydrogen electrode. Such activity and selectivity to FDCA are attributed to the fast electron transfer, high electrochemical surface area, and reduced charge transfer resistance. More impressively, remarkable catalyst stability under long-term testing is obtained with 17 catalytic cycles. This work highlights the rational design of metal oxides with ordered meso-structures for electrochemical biomass conversion. © 2021 The Authors. ChemSusChem published by Wiley-VCH GmbH

Highly selective one-step hydrogenation of phenol to cyclohexanone, an important intermediate in the production of nylon 6 and nylon 66, is desirable but remains a challenge. Pd nanoparticles supported on nitrogen- and oxygen-functionalized carbon nanotubes (NCNTs, OCNTs) were prepared, characterized, and applied in the hydrogenation of phenol to cyclohexanone to study the effect of N-doping. Almost full conversion of phenol with high selectivity to cyclohexanone was achieved over Pd/NCNT under mild reaction conditions using either H2 or formic acid (FA) as a hydrogen source. The effects of reaction temperature and FA/phenol ratio and the reusability were investigated. Separate FA decomposition experiments without and with the addition of phenol were performed to investigate the reaction mechanism, especially the deactivation behavior. Deactivation was observed for both catalysts during the FA decomposition, while only Pd/OCNT rather than Pd/NCNT was deactivated in the transfer hydrogenation with FA and the FA decomposition in the presence of phenol, indicating the unique role of N-doping. Therefore, we assume that deactivation is caused by the strongly bound formates on the active Pd sites, suppressing further FA decomposition and/or transfer hydrogenation on Pd. The nonplanar adsorption of phenol on NCNTs via weak O−H⋅⋅⋅N interactions enables the occurrence of the subsequent hydrogenation by adsorbed formate on Pd. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH

Water electrolysis is a promising technology for sustainable hydrogen production; however, its commercialisation is limited by sluggish kinetics of the oxygen evolution reaction (OER). A potential alternative to the OER is hence required and is seen in the electrocatalytic glycerol oxidation reaction (GOR) as it offers concomitant value-added product generation from a cheap and abundant feedstock. Here, we show a facile solid-state synthesis method to obtain Ni-boride, a non-noble metal-based catalyst subsequently used in an in-depth study of the GOR product distribution as a function of key electrolysis parameters. Highly crystalline, mixed-phase Ni borides were obtained, and their synthesis was successfully optimised regarding GOR activity. Long-term chronoamperometry was conducted in a circular flow-through cell and samples were analysed by HPLC. It is shown that the formation of lactic acid, one of the most valuable GOR products, can be enhanced by optimising the electrolyte composition and the applied potential. © 2021 The Authors. ChemElectroChem published by Wiley-VCH GmbH

NaNbO3 enriched with oxygen vacancies by Ni doping was successfully synthesized via a polymerized complex method and applied as a photocatalyst in the oxidation of cinnamyl alcohol (CA) to cinnamaldehyde in air. Reaction rates as high as 45 μmol h-1 were achieved under visible light with a high apparent quantum efficiency of 67.2% and excellent chemoselectivity larger than 99%. UV-vis, electron paramagnetic resonance, and attenuated total reflectance infrared spectroscopy results indicate that the CA molecules preferentially adsorb at the oxygen vacancies, thus enabling electron transfer between coordinatively bound CA and NaNbO3 under visible light, inducing CA oxidation. The photocatalytic aerobic oxidation of CA is assumed to proceed via the one-photon pathway with H2O2 as the coupled product. The photodeposited Pt nanoparticles on the surface not only enhanced the oxidation rate but also improved the selectivity to cinnamaldehyde substantially because of the fast decomposition of formed H2O2, in this way avoiding its consecutive oxidation by H2O2. The oxygen vacancies on the surface generated by Ni doping are identified to play a decisive role in the chemisorption of cinnamyl alcohol and the interface charge transfer. © 2021 American Chemical Society. All rights reserved.

We report on a photobioelectrochemical fuel cell consisting of a glucose-oxidase-modified BiFeO3 photobiocathode and a quantum-dot-sensitized inverse opal TiO2 photobioanode linked to FAD glucose dehydrogenase via a redox polymer. Both photobioelectrodes are driven by enzymatic glucose conversion. Whereas the photobioanode can collect electrons from sugar oxidation at rather low potential, the photobiocathode shows reduction currents at rather high potential. The electrodes can be arranged in a sandwich-like manner due to the semi-transparent nature of BiFeO3, which also guarantees a simultaneous excitation of the photobioanode when illuminated via the cathode side. This tandem cell can generate electricity under illumination and in the presence of glucose and provides an exceptionally high OCV of about 1 V. The developed semi-artificial system has significant implications for the integration of biocatalysts in photoactive entities for bioenergetic purposes, and it opens up a new path toward generation of electricity from sunlight and (bio)fuels. © 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH

The effects of hydrogen in metals are a pressing issue causing severe economic losses due to material deterioration by hydrogen embrittlement. A crucial understanding of the interactions of hydrogen with different microstructure features can be reached by nanoindentation due to the small volumes probed. Even more, in situ testing while charging the sample with hydrogen prevents the formation of concentration gradients due to hydrogen desorption. Two custom electrochemical cells for in situ testing were built in-house to charge the sample with hydrogen during nanoindentation: “front-side” charging with the sample and the indenter tip immersed into the electrolyte, and “back-side” charging where the analyzed region is never in contact with the solution. During front-side charging, surface degradation often occurs which also negatively influences analyses after hydrogen charging. The back-side charging approach proposed in this work is a promising technique for studying in situ the effects of hydrogen in alloys under mechanical loads, while completely excluding the influence of the electrolyte on the nanoindented surface. Hydrogen diffusion from the charged back-side toward the testing surface is here demonstrated by Kelvin probe measurements in ferritic FeCr alloys, used as a case study due to the high mobility of hydrogen in the bcc lattice. During nanoindentation, a reduction on the shear stress necessary for dislocations nucleation due to hydrogen was observed using both setups; however, the quantitative data differs and a contradictory behavior was found in hardness measurements. Finally, some guidelines for the use of both approaches and a summary of their advantages and disadvantages are presented. Graphical abstract: [Figure not available: see fulltext.] © 2021, The Author(s).

Synthesizing molecule@support hybrids is appealing to improve molecular electrocatalysis. We report herein metal–organic framework (MOF)-supported Co porphyrins for the oxygen reduction reaction (ORR) with improved activity and selectivity. Co porphyrins can be grafted on MOF surfaces through ligand exchange. A variety of porphyrin@MOF hybrids were made using this method. Grafted Co porphyrins showed boosted ORR activity with large (>70 mV) anodic shift of the half-wave potential compared to ungrafted porphyrins. By using active MOFs for peroxide reduction, the number of electrons transferred per O2 increased from 2.65 to 3.70, showing significantly improved selectivity for the 4e ORR. It is demonstrated that H2O2 generated from O2 reduction at Co porphyrins is further reduced at MOF surfaces, leading to improved 4e ORR. As a practical demonstration, these hybrids were used as air electrode catalysts in Zn-air batteries, which exhibited equal performance to that with Pt-based materials. © 2021 Wiley-VCH GmbH

The electrochemical CO2 reduction (CO2R) is a promising approach to decrease the amount of CO2 in the atmosphere by producing commodity chemicals or fuels using renewable energies. Herein, the development of non-noble metal electrocatalysts is regarded as a key point for achieving the transition of CO2R to industrial scales. Transition metal chalcogenides of the pentlandite structure (M9X8) have emerged as promising electrocatalysts to produce syngas. In this line, we present the electrochemical CO2R of FexNi9-xS8 (x=3–6) with variable Fe : Ni ratios. All materials can reduce H2O/CO2 mixtures to CO or H2 respectively with varying efficiency depending on the Fe : Ni ratio and the water content. While CO2R in proton-rich organic electrolytes was mainly accompanied by hydrogen evolution, the CO2R activity climaxed with F.E. of 3.6 % for CO and 0.3 % for methane using Fe3Ni6S8. Using electrolytes with low water content, CO production with F.E. close to 90 % was demonstrated. Counterintuitively, the variation of the Fe : Ni ratio led only to small alterations in the CO2R activity. Quantum mechanical studies were performed to get further information on the observed trends and provide further insight into structure/activity relationships for the Fe/Ni pentlandite system and its CO2R activity opening the path towards the development of more active and robust CO2R electrocatalysts. © 2021 The Authors. ChemElectroChem published by Wiley-VCH GmbH

The H + CH3OH reaction, which plays an important role in combustion and the interstellar medium, presents a prototypical system with multi channels and tight transition states. However, no globally reliable potential energy surface (PES) has been available to date. Here we develop global analytical PESs for this system using the permutation-invariant polynomial neural network (PIP-NN) and the high-dimensional neural network (HD-NN) methods based on a large number of data points calculated at the level of the explicitly correlated unrestricted coupled cluster single, double, and perturbative triple level with the augmented correlation corrected valence triple-ζ basis set (UCCSD(T)-F12a/AVTZ). We demonstrate that both machine learning PESs are able to accurately describe all dynamically relevant reaction channels. At a collision energy of 20 kcal/mol, quasi-classical trajectory calculations reveal that the dominant channel is the hydrogen abstraction from the methyl site, yielding H2 + CH2OH. The reaction of this major channel takes place mainly via the direct rebound mechanism. Both the vibrational and rotational states of the H2 product are relatively cold, and large portions of the available energy are converted into the product translational motion. Copyright © 2020 American Chemical Society.

Strong and ductile materials that have high resistance to corrosion and hydrogen embrittlement are rare and yet essential for realizing safety-critical energy infrastructures, hydrogen-based industries, and transportation solutions. Here we report how we reconcile these constraints in the form of a strong and ductile CoNiV medium-entropy alloy with face-centered cubic structure. It shows high resistance to hydrogen embrittlement at ambient temperature at a strain rate of 10−4 s−1, due to its low hydrogen diffusivity and the deformation twinning that impedes crack propagation. Moreover, a dense oxide film formed on the alloy’s surface reduces the hydrogen uptake rate, and provides high corrosion resistance in dilute sulfuric acid with a corrosion current density below 7 μA cm−2. The combination of load carrying capacity and resistance to harsh environmental conditions may qualify this multi-component alloy as a potential candidate material for sustainable and safe infrastructures and devices. © 2020, The Author(s).

The heterogeneously catalysed reaction of hydrogen with carbon monoxide and carbon dioxide (syngas) to methanol is nearly 100 years old, and the standard methanol catalyst Cu/ZnO/Al2O3 has been applied for more than 50 years. Still, the nature of the Zn species on the metallic Cu0 particles (interface sites) is heavily debated. Here, we show that these Zn species are not metallic, but have a positively charged nature under industrial methanol synthesis conditions. Our kinetic results are based on a self-built high-pressure pulse unit, which allows us to inject selective reversible poisons into the syngas feed passing through a fixed-bed reactor containing an industrial Cu/ZnO/Al2O3 catalyst under high-pressure conditions. This method allows us to perform surface-sensitive operando investigations as a function of the reaction conditions, demonstrating that the rate of methanol formation is only decreased in CO2-containing syngas mixtures when pulsing NH3 or methylamines as basic probe molecules. © 2020, The Author(s).

Pd nanoparticles deposited on nitrogen-doped mesoporous carbon are promising catalysts for highly selective and effective catalytic hydrogenation reactions. To design and utilize these novel catalysts, it is essential to understand the effect of N doping on the metal-support interactions. A combined experimental (X-ray photoelectron spectroscopy) and computational (density functional theory) approach is used to identify preferential adsorption sites and to give detailed explanations of the corresponding metal-support interactions. Pyridinic N atoms turned out to be the preferential adsorption sites for Pd nanoparticles on nitrogen-doped mesoporous carbon, interacting through their lone pairs (LPs) with the Pd atoms via N-LP-Pd dσ and N-LP-Pd s and Pd dπ-π∗ charge transfer, which leads to a change in the Pd oxidation state. Our results evidence the existence of bifunctional palladium nanoparticles containing Pd0 and Pd2+ centers. © the Owner Societies.

The electrocatalytic reduction of carbon dioxide (CO2) by means of renewable energies is widely recognized as a promising approach to establish a sustainable closed carbon cycle economy. However, widespread application is hampered by the inherent difficulty in suppressing the hydrogen evolution reaction and controlling the overall process selectivity. Further critical parameters are the limited solubility of CO2 in many electrolytes and its hindered mass transport to the electrodes. Herein we report on a series of nanoparticle Cu electrocatalysts on different carbon supports and their potential to perform the electrochemical CO2 reduction under supercritical conditions (scCO2). Herein, CO2 serves as the reaction medium and reactant alike. By a detailed comparison to ambient conditions we show that scCO2 conditions largely suppress the undesirable hydrogen evolution and favor the production of formic acid by the Cu electrodes. Furthermore, we show that scCO2 conditions significantly prevent Cu nanoparticle agglomeration during electrocatalysis. © 2020 American Chemical Society.

Several H−H bond forming pathways have been proposed for the hydrogen evolution reaction (HER). Revealing these HER mechanisms is of fundamental importance for the rational design of catalysts and is also extremely challenging. Now, an unparalleled example of switching between homolytic and heterolytic HER mechanisms is reported. Three nickel(II) porphyrins were designed and synthesized with distinct steric effects by introducing bulky amido moieties to ortho- or para-positions of the meso-phenyl groups. These porphyrins exhibited different catalytic HER behaviors. For these Ni porphyrins, although their 1e-reduced forms are active to reduce trifluoroacetic acid, the resulting Ni hydrides (depending on the steric effects of porphyrin rings) have different pathways to make H2. Understanding HER processes, especially controllable switching between homolytic and heterolytic H−H bond formation pathways through molecular engineering, is unprecedented in electrocatalysis. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

[FeFe]-hydrogenases have attracted research for more than twenty years as paragons for the design of new catalysts for the hydrogen evolution reaction (HER). The bridging dithiolate comprising a secondary amine as bridgehead is the key element for the reactivity of native [FeFe]hydrogenases and was therefore the midpoint of hundreds of biomimetic hydrogenase models. However, within those mimics, phosphorous is barely seen as a central element in the azadithiolato bridge despite being the direct heavier homologue of nitrogen. We herein synthesized three new phosphorous based [FeFe]-hydrogenase models by reacting dithiols (HSCH2)2P(O)R (R = Me, OEt, OPh) with Fe3(CO)12. All synthesized mimics show catalytic reactivity regarding HER and change their mechanisms depending on the strength of the used acid. In all presented mimics, the oxide is the center of reactivity, independent of the nature of the bridgehead. However, the phosphorous atom might be reduced by the methods we present herein to alter the reactivity of the model compounds towards protons and oxygen. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.

Bimetallic Co-Cu catalysts are widely applied in higher alcohol synthesis (HAS), but the formation of the final active structure has not yet been fully clarified, especially for Co-rich catalysts. We investigated the structural evolution of a Co-Cu catalyst (Co:Cu = 2) from the hydrotalcite precursor containing additional Al3+ and Zn2+ to the final active state after 80 h under reaction conditions at 280 °C and 60 bar. The reconstruction of the bimetallic Co-Cu nanoparticles obtained by H2 reduction was induced by the feed gas consisting of an equimolar H2 and CO syngas mixture resulting in fast phase separation and sintering of metallic Cu0 and Co0 in the first 2 h time on stream (TOS) and a continuous carbidization of Co0 forming Co2C and its sintering until steady state was reached after 40 h TOS. An intergrowth of metallic Cu0 nanoparticles with Co2C nanoparticles was observed to occur under reaction conditions. The high selectivity to oxygenates amounting to 41% compared with 29% to hydrocarbons is ascribed to the multi-functional Co2C/Cu0 interface enabling dissociative CO adsorption, hydrogenation and CO insertion. The formation of hydrogenated carbon species (CxHy) originating from dissociative CO chemisorption is assumed to be favored by hydrogen spillover from Cu0 to Co2C. The adsorption sites for molecular CO provided by both Cu0 and Co2C facilitate its insertion into the CxHy intermediates thus leading to a higher selectivity to alcohols following the Anderson-Schulz-Flory distribution. © 2020 Elsevier Inc.

We investigate the adsorption geometry of a three-dimensional organic molecule, anilino-nitro azobenzene, within hydrogen-bonded supramolecular structures on Au(111) by low temperature scanning tunneling microscopy. Therein, three conformational isomers exist, completely planar trans and cis-isomers and a non-planar, but surface adapted cis-isomer. The anilino-end of the molecule is planar for all isomers. In contrast, the nitro-end of the cis-isomer is only planar, if the nitro-end of the molecule forms hydrogen bonds. Our study pinpoints the subtle balance between molecule-substrate and molecule-molecule interaction in adsorption-induced bond-angle distortion that drive partial or full planarization of the molecule. © 2019 Elsevier B.V.

Thin-film material libraries in the ternary and quaternary metal oxide systems Fe-V-O, Cu-V-O, and Cu-Fe-V-O were synthesized using combinatorial reactive co-sputtering with subsequent annealing in air. Their compositional, structural, and functional properties were assessed using high-throughput characterization methods. Prior to the investigation of the quaternary system Cu-Fe-V-O, the compositions (Fe61V39)Ox and (Cu52V48)Ox with promising photoactivity were identified from their ternary subsystems Fe-V-O and Cu-V-O, respectively. Two Cu-Fe-V-O material libraries with (Cu29-72Fe4-27V22-57)Ox and (Cu11-55Fe27-73V12-34)Ox composition spread were investigated. Seven mixed ternary and quaternary phase regions were identified: I (α-Cu3FeV6O26/FeVO4), II (Cu5V2O10/FeVO4/α-Cu3Fe4V6O26), III (Cu5V2O10), IV (Cu5V2O10/FeVO4, V (FeVO4/γ-Cu2V2O7/α-Cu3Fe4V6O26), VI (β-Cu2V2O7/α-Cu3Fe4V6O26/FeVO4), and VII (β-Cu3Fe4V6O26/FeVO4). In the investigated composition range, two photoactive regions, (Cu53Fe7V40)Ox and (Cu45Fe21V34)Ox, were identified, exhibiting 103 μA/cm2 and 108 μA/cm2 photocurrent density for the oxygen evolution reaction at 1.63 V vs reversible hydrogen electrode, respectively. The highest photoactive region (Cu45Fe21V34)Ox comprises the dominant α-Cu3Fe4V6O24 phase and minor FeVO4 phase. This photoactive region corresponds to having an indirect bandgap of 1.87 eV and a direct bandgap of 2.58 eV with an incident photon-to-current efficiency of 30% at a wavelength of 310 nm. © 2020 Author(s).

The risk of hydrogen embrittlement (HE) is currently one important factor impeding the use of medium Mn steels. However, knowledge about HE in these materials is sparse. Their multiphase microstructure with highly variable phase conditions (e.g. fraction, percolation and dislocation density) and the feature of deformation-driven phase transformation render systematic studies of HE mechanisms challenging. Here we investigate two austenite-ferrite medium Mn steel samples with very different phase characteristics. The first one has a ferritic matrix (~74 vol.% ferrite) with embedded austenite and a high dislocation density (~1014 m−2) in ferrite. The second one has a well recrystallized microstructure consisting of an austenitic matrix (~59 vol.% austenite) and embedded ferrite. We observe that the two types of microstructures show very different response to HE, due to fundamental differences between the HE micromechanisms acting in them. The influence of H in the first type of microstructure is explained by the H-enhanced local plastic flow in ferrite and the resulting increased strain incompatibility between ferrite and the adjacent phase mixture of austenite and strain-induced α'-martensite. In the second type of microstructure, the dominant role of H lies in its decohesion effect on phase and grain boundaries, due to the initially trapped H at the interfaces and subsequent H migration driven by deformation-induced austenite-to-martensite transformation. The fundamental change in the prevalent HE mechanisms between these two microstructures is related to the spatial distribution of H within them. This observation provides significant insights for future microstructural design towards higher HE resistance of high-strength steels. © 2019

Highly sensitive and selective hydrogen sulfide (H2S) sensors based on hierarchical highly ordered SnO2 nanobowl branched ZnO nanowires (NWs) were synthesized via a sequential process combining hard template processing, atomic-layer deposition, and hydrothermal processing. The hierarchical sensing materials were prepared in situ on microelectromechanical systems, which are expected to achieve high-performance gas sensors with superior sensitivity, long-term stability and repeatability, as well as low power consumption. Specifically, the hierarchical nanobowl SnO2@ZnO NW sensor displayed a high sensitivity of 6.24, a fast response and recovery speed (i.e., 14 s and 39 s, respectively), and an excellent selectivity when detecting 1 ppm H2S at 250 °C, whose rate of resistance change (i.e., 5.24) is 2.6 times higher than that of the pristine SnO2 nanobowl sensor. The improved sensing performance could be attributed to the increased specific surface area, the formation of heterojunctions and homojunctions, as well as the additional reaction between ZnO and H2S, which were confirmed by electrochemical characterization and band alignment analysis. Moreover, the well-structured hierarchical sensors maintained stable performance after a month, suggesting excellent stability and repeatability. In summary, such well-designed hierarchical highly ordered nanobowl SnO2@ZnO NW gas sensors demonstrate favorable potential for enhanced sensitive and selective H2S detection with long-term stability and repeatability. © 2020, The Author(s).

Photoelectrochemical (PEC) water splitting is a promising approach to drive green, carbon-free production of hydrogen (H2). In ‘classic’ water splitting, oxygen (O2) is formed at the anode as a by-product. It has been suggested that substitution of anodic O2production with hydrogen peroxide (H2O2) could increase the financial attractiveness of PEC water splitting. Here, we present a techno-economic analysis of a photoelectrochemical H2/H2O2process. Specifically, we model photoelectrochemical farms with industrially relevant production capacities. Two scenarios are considered: (i) a theoretical scenario with an optimal solar-to-hydrogen (STH) efficiency of 27.55% and (ii) a literature-based state-of-the-art scenario with an STH efficiency of 10.1%. When applying an averaged market value of $0.85 kg−1for H2O2, the analysis reveals a negative levelized cost of hydrogen (LCH) for scenario (i),i.e.$6.45 kg−1, and for scenario (ii) an LCH of $6.19 kg−1. Our results imply that these values are superior to the LCH of ‘classic’ PEC water splitting (ca.$10 kg−1), while the negative value for scenario (i) even outcompetes the LCH of steam methane reforming ($1.4 kg−1). We predict that significant reduction in the LCH can be realized within the PEC community when future research is aimed at enhancing the stability of the photoanode and optimizing the STH efficiency for anodic H2O2formation. This manuscript clearly demonstrates the financial benefits of value-added product formation, such as hydrogen peroxide, over O2formation. In a broader context, our analysis verifies that further research on valuable commodity chemicals at the anode in water splitting and CO2reduction should be stimulated in the future to facilitate implementation of emerging, cost-intensive technologies. © The Royal Society of Chemistry 2020.

Elemental copper can be utilized to generate C-C bonds in order to synthesize nanographenes in a mechanochemical environment. Utilizing the solvent-free environment of a ball mill, we present a facile and highly sustainable concept for the internal C-C coupling in oligo-phenyls on the example of triphenylene and extend it to the transformation of hexaphenylbenzene into hexa-peri-hexabenzocoronene as a benchmark nanographene. © 2020 American Chemical Society.

An electrosurgical argon plasma with a 5% admixture of molecular hydrogen is studied in order to investigate time averaged plasma parameters by optical emission spectroscopy (OES). Electron densities in the range of 1015-1016 cm-3 are determined from the Stark broadening of the time averaged line profiles of the Balmer-α and -β emission lines of hydrogen. A two-profile fit corresponding to regions of different electron densities is found to provide a better representation of the line broadening than a single profile fit. This is consistent with time resolved ICCD imaging, acquired with 150 ns time resolution, that shows strong radial gradients in the plasma emission and the asymmetry produced by the discharge arrangement. Gas temperatures are determined using two different methods. Firstly, simulated spectra for different rotational temperatures are fitted to the measured N2(C-B, 0-1) emission band originating from ambient air diffusion into the argon/hydrogen gas flow. From the best fit, rotational temperatures between 1500 K and 1800 K are inferred. These measurements are in good agreement with those inferred by the second method, which is based on the collisional broadening of the emission lines of neutral argon at 750 nm and 751 nm. This latter method may be useful for the measurement of gas temperatures when the device is used inside hollow organs during endoscopic or laparoscopic interventions, where air mixing will be limited. Therefore, the results of this study are highly relevant to applications of these devices, e.g. for controlling tissue effects and the avoidance of excessive heating. © 2020 IOP Publishing Ltd.

We describe the fabrication of gas diffusion electrodes modified with polymer/enzyme layers for electroenzymatic CO2 fixation. For this, a metal-free organic low-potential viologen-modified polymer has been synthesized that reveals a redox potential of around-0.39 V vs SHE and is thus able to electrically wire W-dependent formate dehydrogenase from Desulfovibrio vulgaris Hildenborough, which reversibly catalyzes the conversion of CO2 to formate. The use of gas diffusion electrodes eliminates limitations arising from slow mass transport when solid carbonate is used as CO2 source. The electrodes showed satisfactory stability that allowed for their long-term electrolysis application for electroenzymatic formate production. Copyright © 2019 American Chemical Society.

Monometallic Mo and W carbides as well as highly mixed (Mo,W) carbides with various Mo/W ratios were synthesized directly on oxygen-functionalized carbon nanotubes (OCNTs), and used as noble-metal-free electrocatalysts in the hydrogen evolution reaction (HER) under both acidic and alkaline conditions. A purely orthorhombic structure was found in both monometallic and mixed carbide samples by X-ray diffraction. Transmission electron microscopy images showed that the carbide particles were highly dispersed on the OCNTs with well-controlled particle size. The homogeneous distribution of Mo and W in the carbides was confirmed by elemental mapping. (Mo,W)2C/OCNT with a Mo/W ratio of 3 : 1 showed the lowest overpotential to reach a current density of 10 mA/cm2 (87 mV in 0.1 M KOH and 92 mV in 0.5 M H2SO4), and the smallest Tafel slope of 34 mV/dec. Long-term stability under both alkaline and acidic conditions was demonstrated for 24 h. Our results revealed that an optimal amount of W in the mixed carbide can significantly improve its performance in the HER following the Tafel reaction pathway, most likely due to the weakened Mo−Hads bond. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

In this work, we study the influence of hydrogen on the deformation behavior and microstructure evolution in an equiatomic CoCrNi medium entropy alloy (MEA) with an ultimate tensile strength of ∼1 GPa. Upon deformation, hydrogen-charged samples exhibit enhanced dislocation activity and nanotwinning. Hydrogen shows both positive and negative effects on the deformation behavior of the CoCrNi MEA. More specifically, it weakens grain boundaries during loading, leading to intergranular cracking. Also, it promotes the formation of twins which enhance the material's resistance to crack propagation. The underlying mechanisms responsible for the hydrogen resistance of the CoCrNi MEA are discussed in detail. © 2020 Elsevier Ltd

The kinetics of higher alcohol synthesis was investigated using a hydrotalcite-derived Co-Cu-based catalyst aiming at a deeper understanding of the complex reaction network. At steady state similar chain growth probabilities of about 0.4 according to the Anderson-Schulz-Flory distribution were observed for alcohols, hydrocarbons and olefins indicating common intermediates. Alkanes were found to be formed consecutively from primarily formed olefins. The observed decrease of the selectivities to alcohols with increasing CO conversion at higher temperatures and higher residence times is ascribed to an increased availability of adsorbed atomic hydrogen, which decreases the saturated coverage of CO-derived CxHyOz species favoring hydrocarbon formation. Correspondingly, reaction orders of 0 and 0.8 for CO and H2, respectively, were derived based on a power-law approach including an apparent activation energy of 140 kJ mol−1. A reaction network based on the CO insertion factor was established, in which the competing reactions β-hydrogen elimination, chain growth and CO insertion proceed from common adsorbed CxHy intermediates. Selective higher alcohol formation was favored at low temperatures and short residence times, high pressures and a moderate H2:CO ratio of 1 requiring a compromise between conversion and selectivity. © 2020 Elsevier Inc.

Hydrogen embrittlement, which severely affects structural materials such as steel, comprises several mechanisms at the atomic level. One of them is hydrogen enhanced decohesion (HEDE), the phenomenon of H accumulation between cleavage planes, where it reduces the interplanar cohesion. Grain boundaries are expected to play a significant role for HEDE, since they act as trapping sites for hydrogen. To elucidate this mechanism, we present the results of first-principles studies of the H effect on the cohesive strength of α-Fe single crystal (001) and (111) cleavage planes, as well as on the Σ5(310)[001] and Σ3(112)[1¯10] symmetrical tilt grain boundaries. The calculated results show that, within the studied range of concentrations, the single crystal cleavage planes are much more sensitive to a change in H concentration than the grain boundaries. Since there are two main types of procedures to perform ab initio tensile tests, different in whether or not to allow the relaxation of atomic positions, which can affect the quantitative and qualitative results, these methods are revisited to determine their effect on the predicted cohesive strength of segregated interfaces. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.

Mesenchymal stromal cells are promising candidates for regenerative applications upon treatment of bone defects. Bone marrow-derived stromal cells (BMSCs) are limited by yield and donor morbidity but show superior osteogenic capacity compared to adipose-derived stromal cells (ASCs), which are highly abundant and easy to harvest. The underlying reasons for this difference on a proteomic level have not been studied yet. Human ASCs and BMSCs were characterized by FACS analysis and tri-lineage differentiation, followed by an intraindividual comparative proteomic analysis upon osteogenic differentiation. Results of the proteomic analysis were followed by functional pathway analysis. 29 patients were included with a total of 58 specimen analysed. In these, out of 5148 identified proteins 2095 could be quantified in >80% of samples of both cell types, 427 in >80% of ASCs only and 102 in >80% of BMSCs only. 281 proteins were differentially regulated with a fold change of >1.5 of which 204 were higher abundant in BMSCs and 77 in ASCs. Integrin cell surface interactions were the most overrepresented pathway with 5 integrins being among the proteins with highest fold change. Integrin 11a, a known key protein for osteogenesis, could be identified as strongly up-regulated in BMSC confirmed by Western blotting. The integrin expression profile is one of the key distinctive features of osteogenic differentiated BMSCs and ASCs. Thus, they represent a promising target for modifications of ASCs aiming to improve their osteogenic capacity and approximate them to that of BMSCs. © 2020 The Authors. Journal of Cellular and Molecular Medicine published by Foundation for Cellular and Molecular Medicine and John Wiley & Sons Ltd

Hydrogen abstraction is one of the crucial initial key steps in the combustion of polycyclic aromatic hydrocarbons. For an accurate theoretical prediction of heterogeneous combustion processes, larger systems need to be treated as compared to pure gas phase reactions. We address here the question on how transferable activation and reaction energies computed for small molecular models are to larger polyaromatics. The approximate transferability of energy contributions is a key assumption for multiscale modeling approaches. To identify efficient levels of accuracy, we start with accurate coupled-cluster and density functional theory (DFT) calculations for different sizes of polyaromatics. More approximate methods as the reactive force-field ReaxFF and the extended semi-empirical tight binding (xTB) methods are then benchmarked against these data sets in terms of reaction energies and equilibrium geometries. Furthermore, we analyze the role of bond-breaking and relaxation energies, vibrational contributions, and post-Hartree-Fock correlation corrections on the reaction, and for the activation energies, we analyze the validity of the Bell-Evans-Polanyi and Hammond principles. First, we find good transferability for this process and that the predictivity of small models at high theoretical levels is way superior than any approximate method can deliver. Second, ReaxFF can serve as a qualitative exploration method, whereas GFN2-xTB in combination with GFN1-xTB appears as a favorable tool to bridge between DFT and ReaxFF so that we propose a multimethod scheme with employing ReaxFF, GFN1/ GFN2-xTB, DFT, and coupled cluster to cope effectively with such a complex reactive system. © 2020 American Chemical Society

[FeFe] hydrogenases are highly efficient catalysts for reversible dihydrogen evolution. H2 turnover involves different catalytic intermediates including a recently characterized hydride state of the active site (H-cluster). Applying cryogenic infrared and electron paramagnetic resonance spectroscopy to an [FeFe] model hydrogenase from Chlamydomonas reinhardtii (CrHydA1), we have discovered two new hydride intermediates and spectroscopic evidence for a bridging CO ligand in two reduced H-cluster states. Our study provides novel insights into these key intermediates, their relevance for the catalytic cycle of [FeFe] hydrogenase, and novel strategies for exploring these aspects in detail. Copyright © 2020 American Chemical Society.

We report an unprecedented dinuclear catalyst for the electrochemical hydrogen evolution reaction (HER). A macrocyclic porphyrin complex comprising two nickel centres connected via redox mediating linker molecules gives rise to efficient catalysis, significantly outperforming a mononuclear reference catalyst. This journal is © The Royal Society of Chemistry.

Nanosecond plasmas in liquids can initiate chemical processes that are exploited in the fields of water treatment, electrolysis or biomedical applications. The understanding of these chemical processes relies on unraveling the dynamics of the variation of pressures, temperatures and species densities during the different stages of plasma ignition and plasma propagation as well as the conversion of the liquid into the plasma state and the gas phase. This is analyzed by monitoring the emission of nanosecond pulsed plasmas that are generated by high voltages of 20 kV and pulse lengths of 10 ns applied to a tungsten tip with 50 μm diameter immersed in water. The spectra are acquired with a temporal resolution of 2 ns and the emission pattern is modelled by a combination of black body radiation from the hot tungsten tip and the pronounced emission lines of the hydrogen Balmer series. The data indicate two contributions of the hydrogen line radiation that differ with respect to the degree of self-absorption. It is postulated that one contribution originates from a recombination region showing strong self absorption and one contribution from an ionization region showing very little self-absorption. The emission lines from the ionization region are evaluated assuming Stark broadening, that yielded electron densities up to 5 × 1025 m-3. The electron density evolution follows the same trend as the temporal evolution of the voltage applied to the tungsten tip. The propagation mechanism of the plasma is similar to that of a positive streamer in the gas phase, although in the liquid phase field effects such as electron transport by tunneling should play an important role. © 2020 The Author(s). Published by IOP Publishing Ltd.

Electrochemical dealloying as a post-Treatment can greatly improve the catalytic activity of nanoparticles. To date, selecting suitable conditions to reach desired porosity, composition and catalytic activity is based on trial-And-error-Attempts, due to insufficient understanding of the electrochemically induced morphological and compositional changes of the nanoparticles. These changes are elucidated here by combining electrochemistry with identical location electron microscopy analyses and linking them to the electrocatalytic properties of the obtained nanocatalysts. Using AgAu alloy nanoparticles and the hydrogen evolution reaction as a model system, the influence of cyclic voltammetry parameters on the catalytic activity upon electrochemical dealloying is investigated. Increasing the number of cycles initially results in a decreased Ag content and a sharp improvement in activity. Additional dealloying increases the nanoparticle porosity, while marginally altering their composition, due to surface motion of atoms. Since this is accompanied by particle aggregation, a decrease in catalytic activity results upon extensive cycling. This transition between porosity formation and particle aggregation marks the optimum for nanocatalyst post-production. The gained insights may aid speeding up the development of new materials by electrochemical dealloying as an easy-To-control post-processing route to tune the properties of existing nanoparticles, instead of having to alter usually delicate synthesis routes as a whole. © The Royal Society of Chemistry.

Among the numerous homogeneous electrochemical CO2 reduction catalysts, [Ni(cyclam)]2+ is known as one of the most potent catalysts. Likewise, [Ni(isocyclam)]2+ was reported to enable electrochemical CO2 conversion but has received significantly less attention. However, for both catalysts, a purposeful substitution of a single nitrogen donor group by chalcogen atoms was never reported. In this work, we report a series of isocyclam-based Ni complexes with {ON3}, {SN3}, {SeN3}, and {N4} moieties and investigated the influence of nitrogen/chalcogen substitution on electrochemical CO2 reduction. While [Ni(isocyclam)]2+ showed the highest selectivity toward CO2 reduction within this series with a Faradaic efficiency of 86% for the generation of CO at an overpotential of-1.20 V and acts as a homogeneous catalyst, the O-and S-containing Ni complexes revealed comparable catalytic activities at ca. 0.3 V milder overpotential but tend to form deposits on the electrode, acting as precursors for a heterogeneous catalysis. Moreover, the heterogeneous species generated from the O-and S-containing complexes enable a catalytic hydride transfer to acetonitrile, resulting in the generation of acetaldehyde. The incorporation of selenium, however, resulted in loss of CO2 reduction activity, mainly leading to hydrogen generation that is also catalyzed by a heterogeneous electrodeposit. Copyright © 2020 American Chemical Society.

While [Ni(cyclam)]2+ and [Ni(dithiacyclam)]2+ complexes were shown to be potent electrocatalysts for the CO2 conversion, their respective Co complexes hitherto received only little attention. Herein, we report on the CoII complexes of the cyclam and dithiacyclam platform, describe their synthesis and reveal their rich solvent dependent coordination chemistry. We show that sulfur implementation into the cyclam moiety leads to a switch from a low spin CoII complex in [Co(cyclam)]2+ to a high spin form in [Co(dithiacyclam)]2+. Notably, while both complexes are capable to perform the reduction of CO2 to CO, H2 formation is generally preferred. Along this line, the complexes were shown to enable proton reduction from acetic acid. However, in comparison to [Co(cyclam)]2+, the altered electronics make [Co(dithiacyclam)]2+ complexes prone to deposit on the glassy carbon working electrode over time leading to an overall low faradaic efficiency for the reduction of protons or CO2. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Observing solute hydrogen (H) in matter is a formidable challenge, yet, enabling quantitative imaging of H at the atomic-scale is critical to understand its deleterious influence on the mechanical strength of many metallic alloys that has resulted in many catastrophic failures of engineering parts and structures. Here, we report on the APT analysis of hydrogen (H) and deuterium (D) within the nanostructure of an ultra-high strength steel with high resistance to hydrogen embrittlement. Cold drawn, severely deformed pearlitic steel wires (Fe–0.98C–0.31Mn–0.20Si–0.20Cr–0.01Cu–0.006P–0.007S wt%, ε=3.1) contains cementite decomposed during the pre-deformation of the alloy and ferrite. We find H and D within the decomposed cementite, and at some interfaces with the surrounding ferrite. To ascertain the origin of the H/D signal obtained in APT, we explored a series of experimental workflows including cryogenic specimen preparation and cryogenic-vacuum transfer from the preparation into a state-of-the-art atom probe. Our study points to the critical role of the preparation, i.e. the possible saturation of H-trapping sites during electrochemical polishing, how these can be alleviated by the use of an outgassing treatment, cryogenic preparation and transfer prior to charging. Accommodation of large amounts of H in the under-stoichiometric carbide likely explains the resistance of pearlite against hydrogen embrittlement. © 2020 Acta Materialia Inc.

The suitability of a commercial and industrially applied Cu-based catalyst for the synthesis of methanol by CO2 hydrogenation was investigated. Unexpectedly, this system showed high stability and well-performance under conditions that may be relevant for chemical energy conversion using hydrogen and energy from renewable technologies. This Cu-based catalyst demonstrated excellent suitability for dynamical process operation that may be essential for effective compensation of the volatility of renewable energy sources. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Molecular design to improve catalyst performance is significant but challenging. In enzymes, residue groups that are close to reaction centers play critical roles in regulating activities. Using this bioinspired strategy, three water-soluble polymers were designed with appending Co porphyrins and different side-chain groups to mimic enzyme reaction centers and activity-controlling residue groups, respectively. With these polymers, high hydrogen evolution efficiency was achieved in neutral aqueous media for electro- (turnover frequency >2.3×104 s−1) and photocatalysis (turnover number >2.7×104). Porphyrin units are surrounded and protected by polymer chains, and more importantly, the activity can be tuned with different side-chain groups. Therefore, instead of revising molecular structures that is difficult from both design and synthesis points of view, polymers can be used to improve molecular solubility and stability and simultaneously regulate activity by using side-chain groups. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Functionalization of semiconductors by metallic nanoparticle is considered to be one of the most effective procedure to improve photocatalytic hydrogen production. Photodeposition is frequently used for functionalization but particle sizes and dispersions are still difficult to control. Here, Pt functionalization is achieved in a one-pot synthesis. The as-prepared samples are compared to reference materials prepared by conventional photodeposition and our results confirm that small and well-dispersed nanoparticles with superior stability are obtained by one-pot synthesis. The enhanced stability is attributed to a limited leaching of Pt nanoparticles during illumination likely caused by the preferable interaction of small, well dispersed Pt nanoparticles with the TiO2 support material. In addition, our results demonstrate that Na-residues are detrimental for the photocatalytic performance and washing in acidic solution is mandatory to effectively reduce the sodium contamination. © 2019 Elsevier B.V.

Biomass-derived 5-hydroxymethylfurfural (HMF) is regarded as one of the most promising platform chemicals to produce 2,5-dimethylfuran (DMF) as a potential liquid transportation fuel. Pd nanoparticles supported on N-containing and N-free mesoporous carbon materials were prepared, characterized, and applied in the hydrogenolysis of HMF to DMF under mild reaction conditions. Quantitative conversion of HMF to DMF was achieved in the presence of formic acid (FA) and H2 over Pd/NMC within 2 h. The reaction mechanism, especially the multiple roles of FA, was explored through a detailed comparative study by varying hydrogen source, additive, and substrate as well as by applying in situ ATR-IR spectroscopy. The major role of FA is to shift the dominant reaction pathway from the hydrogenation of the aldehyde group to the hydrogenolysis of the hydroxymethyl group via the protonation by FA at the C-OH group, lowering the activation barrier of the C−O bond cleavage and thus significantly enhancing the reaction rate. XPS results and DFT calculations revealed that Pd2+ species interacting with pyridine-like N atoms significantly enhance the selective hydrogenolysis of the C−OH bond in the presence of FA due to their high ability for the activation of FA and the stabilization of H−. © 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH

Variants of the highly active [NiFeSe] hydrogenase from D. vulgaris Hildenborough that exhibit enhanced O2 tolerance were used as H2-oxidation catalysts in H2/O2 biofuel cells. Two [NiFeSe] variants were electrically wired by means of low-potential viologen-modified redox polymers and evaluated with respect to H2-oxidation and stability against O2 in the immobilized state. The two variants showed maximum current densities of (450±84) μA cm−2 for G491A and (476±172) μA cm−2 for variant G941S on glassy carbon electrodes and a higher O2 tolerance than the wild type. In addition, the polymer protected the enzyme from O2 damage and high-potential inactivation, establishing a triple protection for the bioanode. The use of gas-diffusion bioanodes provided current densities for H2-oxidation of up to 6.3 mA cm−2. Combination of the gas-diffusion bioanode with a bilirubin oxidase-based gas-diffusion O2-reducing biocathode in a membrane-free biofuel cell under anode-limiting conditions showed unprecedented benchmark power densities of 4.4 mW cm−2 at 0.7 V and an open-circuit voltage of 1.14 V even at moderate catalyst loadings, outperforming the previously reported system obtained with the [NiFeSe] wild type and the [NiFe] hydrogenase from D. vulgaris Miyazaki F. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

The incorporation of highly active but also highly sensitive catalysts (e.g. the [FeFe] hydrogenase from Desulfovibrio desulfuricans) in biofuel cells is still one of the major challenges in sustainable energy conversion. We report the fabrication of a dual-gas diffusion electrode H2/O2 biofuel cell equipped with a [FeFe] hydrogenase/redox polymer-based high-current-density H2-oxidation bioanode. The bioanodes show benchmark current densities of around 14 mA cm−2 and the corresponding fuel cell tests exhibit a benchmark for a hydrogenase/redox polymer-based biofuel cell with outstanding power densities of 5.4 mW cm−2 at 0.7 V cell voltage. Furthermore, the highly sensitive [FeFe] hydrogenase is protected against oxygen damage by the redox polymer and can function under 5 % O2. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Polycrystalline MoS2 from (NH4)2MoS4 thermolysis was activated in dilute H2 at 523 K < TR < 873 K and studied by XRD, total scattering analysis, XPS, HRTEM, and chemisorption to explain, why coordinative unsaturation decreases with growing TR contrary to expectations from the MoS2 structure. Hydrogenation rates were measured for identifying active sites. With increasing TR, activity and chemisorption peaked at different TR,peak. Below TR,peak, increasing activity was not paralleled by changes in MoS2 microstructure. Decreasing chemisorption above TR,peak was assigned to saturation of vacancies by sulfide from internal defects and to inclusion of vacancies in the interior of aggregates. Upon high-temperature reduction, stacks grew anisotropically (basal planes extended), retaining defects like bending, turbostratic disorder. Preferential exposure of stack bases in aggregate surfaces resulted in enhanced decrease of chemisorption. Correlations between activity, edge area and (b)rim length estimated from a morphological model localized active sites in the (b)rim region. © 2020 Elsevier B.V.

Metal-rich chalcogenides composed of highly abundant elements recently emerged as promising catalysts for the electrocatalytic hydrogen evolution reaction (HER). Many of these materials benefit from a high intrinsic conductivity as compared to their chalcogen-rich congeners, greatly reducing the necessity for conductive additives or sophisticated nanostructuring. Herein, we showcase the high potential of metal-rich transition-metal chalcogenides for the electrocatalytic hydrogen formation by summarizing the recent progress achieved with M9S8 (pentlandite type) and M3S2 (heazlewoodite type) based materials, which represent the most frequently applied compositions for this purpose. By a detailed electrochemical comparison of bulk as well as pellet electrodes of metal-rich Fe4.5Ni4.5S8, we also aim at raising awareness in the community for the inherent differences in catalytic properties of the materials themselves and those of the fabricated electrodes, a point that is often disregarded in reports on HER-catalyst systems. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Breakthroughs toward effective water-splitting electrocatalysts for mass hydrogen production will necessitate material design strategies based on unexplored material chemistries. Herein, Ni-metalloid (B, Si, P, As, Te) alloys are reported as an emergent class of highly promising electrocatalysts for the oxygen evolution reaction (OER) and insight is offered into the origin of activity enhancement on the premise of the surface electronic structure, the OER activation energy, influence of the guest metalloid elements on the lattice structure of the host metal (Ni), and surface-oxidized metalloid oxoanions. The metalloids modify the lattice structure of Ni, causing changes in the nearest Ni–Ni interatomic distance (dNi–Ni). The activation energy Ea scales with dNi–Ni indicating an apparent dependence of the OER activity on lattice properties. During the OER, surface Ni atoms are oxidized to nickel oxyhydroxide, which is the active state of the catalyst, meanwhile, the surface metalloids are oxidized to the corresponding oxoanions that affect the interfacial electrode/electrolyte properties and hence the adsorption/desorption interaction energies of the reacting species. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Hydrogenases are metalloenzymes that catalyze the conversion of protons and molecular hydrogen, H2. [FeFe]-hydrogenases show particularly high rates of hydrogen turnover and have inspired numerous compounds for biomimetic H2 production. Two decades of research on the active site cofactor of [FeFe]-hydrogenases have put forward multiple models of the catalytic proceedings. In comparison, our understanding of proton transfer is poor. Previously, residues were identified forming a hydrogen-bonding network between active site cofactor and bulk solvent; however, the exact mechanism of catalytic proton transfer remained inconclusive. Here, we employ in situ infrared difference spectroscopy on the [FeFe]-hydrogenase from Chlamydomonas reinhardtii evaluating dynamic changes in the hydrogen-bonding network upon photoreduction. While proton transfer appears to be impaired in the oxidized state (Hox), the presented data support continuous proton transfer in the reduced state (Hred). Our analysis allows for a direct, molecular unique assignment to individual amino acid residues. We found that transient protonation changes of glutamic acid residue E141 and, most notably, arginine R148 facilitate bidirectional proton transfer in [FeFe]-hydrogenases. © 2019 American Chemical Society.

Interfaces between water and metal oxides exhibit many interesting phenomena like dissociation and recombination of water molecules and water exchange between the interface and the bulk liquid. Moreover, a variety of structural motifs can be found, differing in hydrogen-bonding patterns and molecular orientations. Here, we report the structure and dynamics of liquid water interacting with the two most stable ZnO surfaces, (101Ì) and (112Ì), by means of reactive molecular dynamics simulations based on a machine learning high-dimensional neural network potential. For both surfaces, three distinct hydration layers can be observed within 10 Å from the surface with the first hydration layer (nearest to the surface) representing the most interesting region to investigate. There, water molecules dynamically dissociate and recombine, leading to a variety of chemical species at the interface. We characterized these species and their molecular environments by analyzing the properties of the hydrogen bonds and local geometries. At ZnO(112Ì0), some of the adsorbed hydroxide ions bridge two surface Zn ions, which is not observed at ZnO(101Ì0). For both surfaces, adsorbed water molecules always bind to a single Zn ion, and those located in proximity of the substrate are mostly "H-down" oriented for ZnO(101Ì0) and "flat-lying", i.e., parallel to the surface, for ZnO(112Ì0). The time scales for proton-transfer (PT) reactions are quite similar at the two surfaces, with the average lifetime of adsorbed hydroxide ions being around 41 ± 3 ps until recombination. However, water exchange events, in which adsorbed water molecules leave the surface and enter the bulk liquid, happen more frequently at ZnO(112Ì0) than at ZnO(101Ì0). © 2018 American Chemical Society.

The direct growth of Pt islands on lattice mismatched Ni nanoparticles is a major synthetic challenge and a promising strategy to create highly strained Pt atoms for electrocatalysis. By using very mild reaction conditions, Pt islands with tunable strain were formed directly on Ni branched particles. The highly strained 1.9 nm Pt-island on branched Ni nanoparticles exhibited high specific activity and the highest mass activity for hydrogen evolution (HER) in a pH 13 electrolyte. These results show the ability to synthetically tune the size of the Pt islands to control the strain to give higher HER activity. Copyright © 2019 American Chemical Society.

Hydrogen pick-up leading to hydride formation is often observed in commercially pure Ti (CP-Ti) and Ti-based alloys prepared for microscopic observation by conventional methods, such as electro-polishing and room temperature focused ion beam (FIB) milling. Here, we demonstrate that cryogenic FIB milling can effectively prevent undesired hydrogen pick-up. Specimens of CP-Ti and a Ti dual-phase alloy (Ti-6Al-2Sn-4Zr-6Mo, Ti6246, in wt.%) were prepared using a xenon-plasma FIB microscope equipped with a cryogenic stage reaching −135 °C. Transmission electron microscopy (TEM), selected area electron diffraction, and scanning TEM indicated no hydride formation in cryo-milled CP-Ti lamellae. Atom probe tomography further demonstrated that cryo-FIB significantly reduces hydrogen levels within the Ti6246 matrix compared with conventional methods. Supported by molecular dynamics simulations, we show that significantly lowering the thermal activation for H diffusion inhibits undesired environmental hydrogen pick-up during preparation and prevents pre-charged hydrogen from diffusing out of the sample, allowing for hydrogen embrittlement mechanisms of Ti-based alloys to be investigated at the nanoscale. © 2019, The Author(s).

An extensive characterization of Co3(PO4)2 was performed by topological analysis according to Bader‘s Quantum Theory of Atoms in Molecules from the experimentally and theoretically determined electron density. This study sheds light on the reactivity of cobalt orthophosphate as a solid-state heterogeneous oxidative-dehydration and -dehydrogenation catalyst. Various faces of the bulk catalyst were identified as possible reactive sites given their topological properties. The charge accumulations and depletions around the two independent five- and sixfold-coordinated cobalt atoms, found in the topological analysis, are correlated to the orientation and population of the d-orbitals. It is shown that the (011) face has the best structural features for catalysis. Fivefold-coordinated ions in close proximity to advantageously oriented vacant coordination sites and electron depletions suit the oxygen lone pairs of the reactant, mainly for chemisorption. This is confirmed both from the multipole refinement as well as from density functional theory calculations. Nearby basic phosphate ions are readily available for C−H activation. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Thermodynamic properties of liquid water as well as hexagonal (Ih) and cubic (Ic) ice are predicted based on density functional theory at the hybrid-functional level, rigorously taking into account quantum nuclear motion, anharmonic fluctuations, and proton disorder. This is made possible by combining advanced free-energy methods and state-of-the-art machine-learning techniques. The ab initio description leads to structural properties in excellent agreement with experiments and reliable estimates of the melting points of light and heavy water. We observe that nuclear-quantum effects contribute a crucial 0.2 meV/H 2 O to the stability of ice Ih, making it more stable than ice Ic. Our computational approach is general and transferable, providing a comprehensive framework for quantitative predictions of ab initio thermodynamic properties using machine-learning potentials as an intermediate step. © 2019 National Academy of Sciences. All rights reserved.

The kinetics of glycerol hydrodeoxygenation to 1,2-propanediol via the selective cleavage of the primary C-O bond was systematically studied in the aqueous phase over a co-precipitated Cu/ZrO2 catalyst. Unsupported pure metallic Cu was used as reference catalyst. Batch experiments were performed in an autoclave by varying the reaction temperature (175–225 °C), H2 partial pressure (25–35 bar) and initial glycerol concentration (2–8 wt%). The Cu/ZrO2 catalyst was found to be highly selective to 1,2propanediol (up to 95%), and ethylene glycol was obtained as major by-product from parallel C–]C bond hydrogenolysis. The apparent activation energies amounting to 106 and 105 kJ mol-1 for Cu/ZrO2 and pure metallic Cu, respectively, of the hydrodeoxygenation pathway provide further evidence for metallic Cu acting as the active site. Kinetic analysis of the rate of glycerol consumption yielded a zero-order dependence on the concentration of glycerol suggesting an essentially almost full coverage of adsorbed glycerol as most strongly bound organic adsorbate. In contrast, a first-order dependence on hydrogen concentration was observed. Hydrogen is assumed to be not only required for the fast hydrogenation of the intermediate acetol, but also for the removal of adsorbed atomic oxygen originating from water dissociation to create empty sites for dissociative glycerol adsorption. Thus, the active Cu sites are assumed to be fully adsorbate-covered under reaction conditions. © 2019 Elsevier B.V.

Gas evolving electrochemical reactions induce bubble formation and growth at surfaces of electrodes. To study one such situation, hydrogen evolution on nickel electrodes, short time chronoamperometric experiments were performed in combination with in-situ microscopy. The entire electrode of 3.14 mm2 was imaged with confocal microscopy and the current response of the electrode then correlated to the observed bubble growth features. Somehow counterintuitively, first a 2–3% increase in current was observed consistently when a bubble grows close to the electrode on the edge of the electrode holder, made of a polymer. This is argued to be due to the removal of surface attached gas from the electrode. Next, we observe a consecutive regime of decreasing current, in which large bubbles accumulate on the surface. Interestingly, when these surface attached bubbles coalesce, a steep change in current is observed, which is accompanied by a burst of small bubbles nucleating on the surface previously occupied by the large bubble. These phenomena are qualitatively discussed on the basis of existing literature, and implications for improvements for electrodes on which gases are produced, are outlined. © The Author(s) 2019.

Electrocatalytically active materials on the industrial as well as on the laboratory scale may suffer from chemical instability during operation, air exposure, or storage in the electrolyte. A strategy to recover the loss of electrocatalytic activity is presented. Oxygen-depolarized cathodes (ODC), analogous to those that are utilized in industrial brine electrolysis, are analyzed: the catalytic activity of the electrodes upon storage (4 weeks) under industrial process conditions (30 wt % NaOH, without operation) diminishes. This phenomenon occurs as a consequence of surface oxidation and pore blockage, as revealed by scanning electron microscopy, focused ion beam milling, X-ray photoelectron spectroscopy, and Raman spectroscopy. Potentiodynamic cycling of the oxidized electrodes to highly reductive potentials and the formation of “nascent” hydrogen re-reduces the electrode material, ultimately recovering the former catalytic activity. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

The kinetics of glycerol hydrodeoxygenation to 1,2-propanediol via the selective cleavage of the primary C-O bond was systematically studied in the aqueous phase over a co-precipitated Cu/ZrO 2 catalyst. Unsupported pure metallic Cu was used as reference catalyst. Batch experiments were performed in an autoclave by varying the reaction temperature (175–225 °C), H 2 partial pressure (25–35 bar) and initial glycerol concentration (2–8 wt%). The Cu/ZrO 2 catalyst was found to be highly selective to 1,2propanediol (up to 95%), and ethylene glycol was obtained as major by-product from parallel C–]C bond hydrogenolysis. The apparent activation energies amounting to 106 and 105 kJ mol -1 for Cu/ZrO 2 and pure metallic Cu, respectively, of the hydrodeoxygenation pathway provide further evidence for metallic Cu acting as the active site. Kinetic analysis of the rate of glycerol consumption yielded a zero-order dependence on the concentration of glycerol suggesting an essentially almost full coverage of adsorbed glycerol as most strongly bound organic adsorbate. In contrast, a first-order dependence on hydrogen concentration was observed. Hydrogen is assumed to be not only required for the fast hydrogenation of the intermediate acetol, but also for the removal of adsorbed atomic oxygen originating from water dissociation to create empty sites for dissociative glycerol adsorption. Thus, the active Cu sites are assumed to be fully adsorbate-covered under reaction conditions. © 2019 Elsevier B.V.

Hydrogen environment embrittlement (HEE) of low-nickel austenitic stainless steels (AISI 300 series) with different chemical compositions was studied focusing on the impact of the steels surface oxides, grain sizes and dislocation arrangements. The susceptibility of the steels to HEE is judged with respect to the relative reduction of area (RRA), where the HEE susceptibility is lower for larger RRA values. For many AISI 300 steels a linear trend is observed correlating RRA and the probability of strain induced martensite formation in tensile tests. Some steels, however, depart from the general trend, revealing greater HEE resistances. A careful examination of possible factors influencing HEE of the investigated steels reveals that high RRA values are linked to a specific type of oxide layer, namely the “high constant level oxide”, as categorized by TOF-SIMS evaluation. Thus, this type of oxide layer may be able to lower the steels HEE susceptibility. Other types of surface oxides, grain sizes and dislocation arrangements in the matrix of the particular AISI 300 steels appear to be of secondary importance. © 2019 Acta Materialia Inc.

We herein present a series of hitherto unprecedented seleno-pentlandites (Fe4.5Ni4.5S8-YSeY). By analysing the influence of S/Se exchange on the catalyst structure and activity in the electrochemical hydrogen evolution reaction we herein showcase the potential and limitations of homologous S/Se exchanges within pentlandite HER catalysts. © 2019 The Royal Society of Chemistry.

We investigate the effect of oxygen vacancies and hydrogen dopants at the surface and inside slabs of LaAlO3, SrTiO3, and LaAlO3/SrTiO3 heterostructures on the electronic properties by means of electronic structure calculations as based on density functional theory. Depending on the concentration, the presence of these defects in a LaAlO3 slab can suppress the surface conductivity. In contrast, in insulating SrTiO3 slabs already very small concentrations of oxygen vacancies or hydrogen dopant atoms induce a finite occupation of the conduction band. Surface defects in insulating LaAlO3/SrTiO3 heterostructure slabs with three LaAlO3 overlayers lead to the emergence of interface conductivity. Calculated defect formation energies reveal strong preference of hydrogen dopant atoms for surface sites for all structures and concentrations considered. Strong decrease of the defect formation energy of hydrogen adatoms with increasing thickness of the LaAlO3 overlayer and crossover from positive to negative values, taken together with the metallic conductivity induced by hydrogen adatoms, seamlessly explains the semiconductor-metal transition observed for these heterostructures as a function of the overlayer thickness. Moreover, we show that the potential drop and concomitant shift of (layer resolved) band edges is suppressed for the metallic configuration. Finally, magnetism with stable local moments, which form atomically thin magnetic layers at the interface, is generated by oxygen vacancies either at the surface or the interface, or by hydrogen atoms buried at the interface. In particular, oxygen vacancies in the TiO2 interface layer cause drastic downshift of the 3d eg states of the Ti atoms neighboring the vacancies, giving rise to strongly localized magnetic moments, which add to the two-dimensional background magnetization. © 2019 IOP Publishing Ltd Printed in the UK.

According to recent experimental research, vanadium-carbide precipitates can improve hydrogen resistance and hardness in steels. In the present article, density functional theory calculations are performed to study the structure and energetics of iron–vanadium carbide interfaces and how hydrogen interacts with them. A comparison of the solubility of hydrogen in different sites shows that hydrogen will tend to segregate towards the iron–vanadium carbide interface and that carbon vacancies within a vanadium carbide precipitate behave as strong hydrogen traps. Additionally, it is shown that the presence of hydrogen at an iron–vanadium carbide interface does not cause a significant embrittlement of the material. © 2019 Hydrogen Energy Publications LLC

[FeFe]-hydrogenases are efficient metalloenzymes that catalyze the oxidation and evolution of molecular hydrogen, H2. They serve as a blueprint for the design of synthetic H2-forming catalysts. [FeFe]-hydrogenases harbor a six-iron cofactor that comprises a [4Fe-4S] cluster and a unique diiron site with cyanide, carbonyl, and hydride ligands. To address the ligand dynamics in catalytic turnover and upon carbon monoxide (CO) inhibition, we replaced the native aminodithiolate group of the diiron site by synthetic dithiolates, inserted into wild-type and amino acid variants of the [FeFe]-hydrogenase HYDA1 from Chlamydomonas reinhardtii. The reactivity with H2 and CO was characterized using in situ and transient infrared spectroscopy, protein crystallography, quantum chemical calculations, and kinetic simulations. All cofactor variants adopted characteristic populations of reduced species in the presence of H2 and showed significant changes in CO inhibition and reactivation kinetics. Differences were attributed to varying interactions between polar ligands and the dithiolate headgroup and/or the environment of the cofactor (i.e., amino acid residues and water molecules). The presented results show how catalytically relevant intermediates are stabilized by inner-sphere hydrogen bonding suggesting that the role of the aminodithiolate group must not be restricted to proton transfer. © 2019 American Chemical Society.

The adsorption of gas-phase pyruvic acid (CH 3 COCOOH) on hydroxylated silica particles has been investigated at 296 K using transmission Fourier transform infrared (FTIR) spectroscopy and theoretical simulations. Under dry conditions (<1% relative humidity, RH), both the trans-cis (Tc) and trans-trans (Tt) pyruvic acid conformers are observed on the surface as well as the (hydrogen bonded) pyruvic acid dimer. The detailed surface interactions were further understood through ab initio molecular dynamics simulations. Under higher relative humidity conditions (above 10% RH), adsorbed water competes for surface adsorption sites. Adsorbed water is also observed to change the relative populations of the different adsorbed pyruvic acid configurations. Overall, this study provides valuable insights into the interaction of pyruvic acid with hydroxylated silica surfaces on the molecular level from both experimental and theoretical analyses. Furthermore, these results highlight the importance of the environment (relative humidity and coadsorbed water) in the adsorption, partitioning, and configurations of pyruvic acid at the surface. Copyright © 2019 American Chemical Society.

The production of acetaldehyde through biomass-derived ethanol dehydrogenation is a sustainable alternative compared to the fossil-feedstock based process, for which Cu-based catalysts are considered to be the most efficient. Herein, we modified the surface of silicon carbide (SiC) to alter the properties of the interface from SiO2-rich to C-rich, and we prepared a series of Cu-supported catalysts (Cu/SiC, Cu/SiO2/SiC, and Cu/C/SiC) with the aim of insight into the effect of the interface structure and composition on catalytic dehydrogenation of ethanol. At 280 °C, the Cu/SiO2/SiC catalyst exhibits high ethanol conversion due to the excellent dispersion of Cu nanoparticles promoted by SiO2-rich interface. In contrast, Cu nanoparticles dispersed on C/SiC shows somewhat lower activity but excellent acetaldehyde selectivity with trace amounts of by-products under identical reaction conditions. This difference is attributed to the fast removal of acetaldehyde because of its low affinity for the relatively inert C-rich interface (C/SiC). This work provides an in-depth understanding of Cu−Si−C multi-interfacial structure and the ethanol dehydrogenation behavior, which may shed light on the design of novel catalysts with tailored interfacial structures. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

[FeFe]-hydrogenases are efficient biological hydrogen conversion catalysts and blueprints for technological fuel production. The relations between substrate interactions and electron/proton transfer events at their unique six-iron cofactor (H-cluster) need to be elucidated. The H-cluster comprises a four-iron cluster, [4Fe4S], linked to a diiron complex, [FeFe]. We combined 57 Fe-specific X-ray nuclear resonance scattering experiments (NFS, nuclear forward scattering; NRVS, nuclear resonance vibrational spectroscopy) with quantum-mechanics/molecular-mechanics computations to study the [FeFe]-hydrogenase HYDA1 from a green alga. Selective 57 Fe labeling at only [4Fe4S] or [FeFe], or at both subcomplexes was achieved by protein expression with a 57 Fe salt and in vitro maturation with a synthetic diiron site precursor containing 57 Fe. H-cluster states were populated under infrared spectroscopy control. NRVS spectral analyses facilitated assignment of the vibrational modes of the cofactor species. This approach revealed the H-cluster structure of the oxidized state (Hox) with a bridging carbon monoxide at [FeFe] and ligand rearrangement in the CO-inhibited state (Hox-CO). Protonation at a cysteine ligand of [4Fe4S] in the oxidized state occurring at low pH (HoxH) was indicated, in contrast to bridging hydride binding at [FeFe] in a one-electron reduced state (Hred). These findings are direct evidence for differential protonation either at the four-iron or diiron subcomplex of the H-cluster. NFS time-traces provided Mössbauer parameters such as the quadrupole splitting energy, which differ among cofactor states, thereby supporting selective protonation at either subcomplex. In combination with data for reduced states showing similar [4Fe4S] protonation as HoxH without (Hred′) or with (Hhyd) a terminal hydride at [FeFe], our results imply that coordination geometry dynamics at the diiron site and proton-coupled electron transfer to either the four-iron or the diiron subcomplex discriminate catalytic and regulatory functions of [FeFe]-hydrogenases. We support a reaction cycle avoiding diiron site geometry changes during rapid H 2 turnover. © 2019 American Chemical Society.

This work investigates the susceptibility of high-interstitial CrMn austenitic stainless steel CN0.96 to hydrogen environment embrittlement. In this context, an N-free model alloy of CN0.96 steel was designed, produced, and characterized. Both steels were subjected to tensile tests in air and in a high-pressure hydrogen gas atmosphere. Both steels undergo severe hydrogen embrittlement. The CN0.96 steel shows trans- and intergranular failure in hydrogen, whereas the N-free model alloy shows exclusively intergranular failure. The different failure modes could be related to different deformation modes that are induced by the presence or absence of N, respectively. In the CN0.96 steel, N promotes planar dislocation slip. Due to the absence of N in the model alloy, localized slip is less pronounced and mechanical twinning is a more preferred deformation mechanism. The embrittlement of the model alloy could therefore be related to mechanisms that are known from hydrogen embrittlement of twinning-induced plasticity steels. © 2019 Hydrogen Energy Publications LLC

Atom probe tomography (APT) has been increasingly used to investigate hydrogen embrittlement in metals due to its unique capacity for direct imaging of H atoms interacting with microstructural features. The quantitativeness of hydrogen measurements by APT is yet to be established in views of erroneous compositional measurements of bulk hydrides and the influence of spurious hydrogen, e.g. residual gas inside the analysis chamber. Here, we analyzed titanium deuteride (approx. 65.0 at%-66.6 at% D) in lieu of hydride to minimize the overlap with residual gas, both with laser pulsing and high-voltage (HV) pulsing. Strategies were deployed to prevent H pick-up during specimen fabrication, including preparing specimens at cryogenic temperature. The measured composition of deuterium by APT with laser pulsing decreases significantly with the applied laser pulse energy, which is interpreted with regards to the strength of the corresponding surface electrostatic field, as assessed by the evolution of charge-state ratio. In contrast, compositional analyses with HV pulsing are roughly independent of the applied experimental parameters, although approx. 15 at%-20 at% off the nominal composition. Aided by plotting paired mass-to-charge correlations, the mechanisms of composition bias in both pulsing modes are discussed. A special emphasis is placed on the local variations of the measured composition as a function of the local electric field across the specimen's surface, which is not uniform due to asymmetric heat distribution related to the localized laser absorption and the faceted nature of surface caused by the crystallographic structure. Our investigations demonstrate the challenges of quantitative analysis of solute deuterium by APT but nevertheless provide insight to achieving the best possible experimental protocol. © 2019 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft.

The performance of nanoporous carbons, used for hydrogen storage, ionic charge storage, or selective gas separation, is strongly determined by their pore shape and size distribution. Two frequently used experimental techniques to characterize the nanopore structure of carbons are gas adsorption combined with quenched-solid density functional theory and small angle X-ray scattering. However, neither of the two techniques can unambiguously derive a valid pore model for disordered pore structures without making assumptions. Here, we quantitatively compare pore size distributions from X-ray scattering and gas adsorption data. We generate three-dimensional pore models of activated carbons using small angle scattering and the concept of Gaussian Random Fields. These pore models are used to generate pore size distributions inherently containing a slit-pore assumption, making them comparable to pore size distributions obtained from gas adsorption analysis. This is realized by probing the effective adsorption potential via sampling of the three-dimensional pore structure with a probing adsorbate and calculating a “Degree of Confinement” parameter accounting for local pore geometry effects. We also generate pore size distributions with an alternative definition of pore size and discuss intricacies of gas adsorption results, such as the general tendency to underestimate the pore size dispersity in disordered microporous carbons. © 2019 Elsevier Ltd

Crystalline Co3O4 nanoparticles with a uniform size of 9 nm as shown by X-ray diffraction (XRD) and transmission electron microscopy (TEM) were synthesized by thermal decomposition of cobalt acetylacetonate in oleylamine and applied in the oxidation of 2-propanol after calcination. The catalytic properties were derived under continuous flow conditions as a function of temperature up to 573 K in a fixed-bed reactor at atmospheric pressure. Temperature-programmed oxidation, desorption (TPD), surface reaction (TPSR), and 2-propanol decomposition experiments were performed to study the interaction of 2-propanol and O2 with the exposed spinel surfaces. Co3O4 selectively catalyzes the oxidative dehydrogenation of 2-propanol, yielding acetone and H2O and only to a minor extent the total oxidation to CO2 and H2O at higher temperatures. The high catalytic activity of Co3O4 reaching nearly full conversion with 100% selectivity to acetone at 430 K is attributed to the high amount of active Co3+ species at the catalyst surface as well as surface-bound reactive oxygen species observed in the O2 TPD, 2-propanol TPD, TPSR, and 2-propanol decomposition experiments. Density functional theory calculations with a Hubbard U term support the identification of the 5-fold-coordinated octahedral surface Co5c3+ as the active site, and oxidative dehydrogenation involving adsorbed atomic oxygen was found to be the energetically most favored pathway. The consumption of surface oxygen and reduction of Co3+ to Co2+ during 2-propanol oxidation derived from X-ray absorption spectroscopy and X-ray photoelectron spectroscopy measurements before and after reaction and poisoning by strongly bound carbonaceous species result in the loss of the low-temperature activity, while the high-temperature reaction pathway remained unaffected. © 2019 American Chemical Society.

Analysis and understanding of the role of hydrogen in metals is a significant challenge for the future of materials science, and this is a clear objective of recent work in the atom probe tomography (APT) community. Isotopic marking by deuteration has often been proposed as the preferred route to enable quantification of hydrogen by APT. Zircaloy-4 was charged electrochemically with hydrogen and deuterium under the same conditions to form large hydrides and deuterides. Our results from a Zr hydride and a Zr deuteride highlight the challenges associated with accurate quantification of hydrogen and deuterium, in particular associated with the overlap of peaks at a low mass-to-charge ratio and of hydrogen/deuterium containing molecular ions. We discuss possible ways to ensure that appropriate information is extracted from APT analysis of hydrogen in zirconium alloy systems that are important for nuclear power applications. Copyright © Microscopy Society of America 2019.

Hydrogen transport behaviour in metals is greatly influenced by the mechanical stress and the underlying microstructural features. In this work, a micromechanical model based on coupled crystal plasticity and hydrogen diffusion is developed and applied to model hydrogen diffusion and storage in a polycrystalline microstructure. Particular emphasis is laid on mechanical influences on hydrogen transport, invoked by internal stresses and by trapping of dislocations generated by plastic strains. First, a study of a precharged material is carried out where hydrogen is allowed to redistribute under the influence of mechanical loading. These simulations demonstrate to which extent hydrogen migrates from regions with compressive strains to those with tensile strains. In the next step, the influence of plastic prestraining on hydrogen diffusion is analysed. This prestraining produces internal residual stresses in the microstructure, that mimic residual stresses introduced into components during cold working. Lastly, a series of permeation simulations is performed to characterise the influence of hydrogen trapping on effective diffusivity. It is shown that the effective diffusivity decreases with stronger traps and the effect is more prominent at a larger predeformation, because the trapped hydrogen concentration increases considerably. The reduction of effective diffusivity with plastic deformation agrees very well with experimental findings and offers a way to validate and parameterise our model. With this work, it is demonstrated how micromechanical modelling can support the understanding of hydrogen transport on the microstructural level. © 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group.

Ingress of hydrogen is often linked to catastrophic failure of Ti-alloys. Here, we quantify the hydrogen distribution in fully β and α + β Ti–Mo alloys by using atom probe tomography. Hydrogen does not segregate at grain boundaries in the fully β sample but segregates at some α/β phase boundaries with a composition exceeding 20 at.% in the α + β sample. No stable hydrides were observed in either sample. The hydrogen concentration in β phases linearly decreases from ~13 at. % to ~4 at. % with increasing Mo-content, which is ascribed to the suppression of hydrogen uptake by Mo addition. © 2018 Elsevier Ltd

Hydrogen embrittlement (HE) of several low-nickel austenitic stainless steels (AISI 300 series) was studied with special attention to the impact of strain induced α′-martensite. The susceptibility of the steels to HE is judged with respect to the relative reduction of area (RRA): The HE susceptibility is lower for larger RRA-values. Strain-induced martensite formation was evaluated within in the framework of the Olson-Cohen model, revealing a linear relationship between RRA and the probability β of martensite nucleus formation in the steels. In order to widen the scope of data evaluation to literature data, the consideration of a parameter alternative to β is required. It is demonstrated that among other parameters the Md30 temperature (Nohara), which assesses the stability against martensitic transformation, can serve as an indicator to predict HE of AISI 300 series steels. Regarding the Md30 temperature (Nohara), a trend-line with respect to the RRA-values is found. Thereby, the RRA-values of low-nickel austenitic stainless steels group into three distinct regimes; (1) for Md30 > −80 °C, where RRA-values decrease with increasing Md30 temperature, (2) at Md30 ≈ −80 °C, where RRA-values show a large variation (‘threshold band’), and (3) for Md30 < −80 °C, showing constant RRA-values of nearly 100%. Some RRA data points that deviate from the trend line can be explained by the special microstructure of the investigated samples. © 2019 Hydrogen Energy Publications LLC

The [FeFe]-hydrogenases catalyze the uptake and evolution of hydrogen with unmatched speed at low overpotential. However, oxygen induces the degradation of the unique [6Fe-6S] cofactor within the active site, termed the H-cluster. We used X-ray structural analyses to determine possible modes of irreversible oxygen-driven inactivation. To this end, we exposed crystals of the [FeFe]-hydrogenase CpI from Clostridium pasteurianum to oxygen and quantitatively investigated the effects on the H-cluster structure over several time points using multiple data sets, while correlating it to decreases in enzyme activity. Our results reveal the loss of specific Fe atoms from both the diiron (2FeH) and the [4Fe-4S] subcluster (4FeH) of the H-cluster. Within the 2FeH, the Fe atom more distal to the 4FeH is strikingly more affected than the more proximal Fe atom. The 4FeH interconverts to a [2Fe-2S] cluster in parts of the population of active CpIADT, but not in crystals of the inactive apoCpI initially lacking the 2FeH. We thus propose two parallel processes: dissociation of the distal Fe atom and 4FeH interconversion. Both pathways appear to play major roles in the oxidative damage of [FeFe]-hydrogenases under electron-donor deprived conditions probed by our experimental setup. Copyright © 2019 American Chemical Society.

Small-punch and nano-indentation tests were used for the first time to probe strength of 500 μm thin Ni50Ti50 shape memory platelets in their hydrogen-free and hydrogen-doped states. Results show excellent reproducibility and suggest that hydrogen penetrates the alloy more efficiently during the cathodic charging at ambient temperatures as compared to heat treatments in a controlled hydrogen atmosphere. Hydrogen content exceeding 100 wtppm results in a retransformation from the B19′ martensite to the R lattice and causes a systematic drop of the rupture strength. The retransformation events in thin surface lamellae were documented by the transmission electron microscopy. © 2018 Elsevier Ltd

Small-punch and nano-indentation tests were used for the first time to probe strength of 500 μm thin Ni 50 Ti 50 shape memory platelets in their hydrogen-free and hydrogen-doped states. Results show excellent reproducibility and suggest that hydrogen penetrates the alloy more efficiently during the cathodic charging at ambient temperatures as compared to heat treatments in a controlled hydrogen atmosphere. Hydrogen content exceeding 100 wtppm results in a retransformation from the B19′ martensite to the R lattice and causes a systematic drop of the rupture strength. The retransformation events in thin surface lamellae were documented by the transmission electron microscopy. © 2018 Elsevier Ltd

In electrochemical production of sodium chlorate from brine solutions, an intriguing function of sodium (di)chromate is to inhibit cathodic reduction of oxychlorides, while maintaining effective reduction of water to form hydrogen. Using an electrochemical Quartz Crystal Microbalance (eQCM) and a Rotating Ring Disk Electrode (RRDE; Au disk, Pt ring), we analyzed the deposition of reduced Cr-species formed from reduction of CrVIO4 2− on Au electrodes. Generally, the current induced by reduction of CrVIO4 2− is significantly larger than the accumulated amount of weight deposited on the Au electrode. Deconvolution of the reductive peak reveals two processes that can be differentiated by varying rotation speed. We therefore propose soluble CrVO4 3− is formed by reduction of CrVIO4 2−, followed by consecutive reduction of CrVO4 3− to primarily soluble CrIII(OH)4 -. Simultaneously, reduction of CrVO4 3− also leads to the formation of a monolayer of CrIII(hydr)oxide. This monolayer significantly inhibits the further reduction of CrVIO4 2−, but allows the film to reach a maximum thickness of approximately 1.85 nm by reduction of surface adsorbed CrVO4 3− and/or de-hydroxylation of CrIII(OH)4 -. The observation that limitation of film growth is due to film-induced inhibition of reduction of CrVIO4 2−, and significant solubility of CrIII(OH)3 in the form of CrIII(OH)4 -, will aid in the search of a non-toxic chrome-free alternative for inhibition of cathodic reduction of oxychlorides and selective hydrogen evolution in the chlorate process. © 2018

The relatively low hydrothermal stability of Al-rich Cu-SSZ-13 catalysts hinders their practical application in ammonia selective catalytic reduction (NH 3 -SCR) reaction. Rare-earth ions were introduced into the Al-rich SSZ-13 zeolite using an organotemplate-free synthesis prior to the exchange of Cu 2+ ions. Among the rare-earth ions tested (Ce, La, Sm, Y, Yb), Y shows significant enhancement of the hydrothermal stability and NH 3 -SCR activities after severe hydrothermal aging at 800 °C for 16 h when compared with Cu-SSZ-13 without Y. Cu-Y-SSZ-13 catalysts with various amounts of Y were prepared, and it is found that with increasing Y content, the low temperature NO conversions can be improved even after hydrothermal aging. SEM-EDX analysis together with two-dimensional multiple quantum magic-angle-spinning nuclear magnetic resonance ( 23 Na MQ MAS NMR) confirms that the Y ions are successfully incorporated into the ion-exchange sites of the SSZ-13 zeolite. Results from 27 Al MAS, 29 Si MAS NMR, temperature-programmed desorption of ammonia (NH 3 -TPD) and quantitative 1 H MAS NMR indicate that Y can stabilize the framework Al and also preserve the Brønsted acid sites in the Al-rich SSZ-13 zeolite. The hydrogen temperature programmed reduction (H 2 -TPR), ultraviolet-visible-near infrared spectroscopy (UV-vis-NIR) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of nitric oxide (NO) or NH 3 adsorption demonstrate that introduction of Y ions causes Cu 2+ ions to preferentially occupy the 6-MR, which has high hydrothermal stability. However, too much of Y may lead to activity loss at both low and high temperatures. The optimized Al-rich Cu-Y-SSZ-13 with 2.8 wt% of copper (Cu) and 1.3 wt% of Y displays almost the same deNO x activities as the conventional organotemplated high silica Cu-SSZ-13 catalyst in a wide reaction temperature window of 150-650 °C after severe hydrothermal treatment. Rare-earth ions could be an effective additive for Cu-SSZ-13 catalysts to further improve their hydrothermal stability for practical applications. © 2019 The Royal Society of Chemistry.

Photocatalytic oxidation of alcohols with high selectivity is a promising approach for the synthesis of organic compounds under mild conditions and for solar energy conversion. In this work, we report on the highly selective anaerobic photooxidation of alcohols to carbonyl compounds with coupled H2 production over Pt-loaded Fe-doped SrTiO3 under visible light. Representatively, an optimized apparent quantum efficiency of 13.2 % at 420 nm was obtained for benzyl alcohol oxidation. X-ray absorption fine structure and in situ diffuse reflectance IR spectroscopy revealed that the surface oxygen vacancies and the fine-tuned valence band edge position induced by Fe doping not only contributed to the activation of α-C−H bonds in alcohols, but also avoided the over-oxidation of the obtained carbonyl compounds. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Photocatalytic oxidation of organic compounds on semiconductors provides a mild approach for organic synthesis and solar energy utilization. Herein, we identify the key points for the photocatalytic oxidation over Pt-loaded Rh-doped strontium titanate allowing the conversion of alcohols efficiently and selectively to aldehydes and ketones under anaerobic conditions and visible light with an apparent quantum efficiency of pure benzyl alcohol oxidation at 420 nm of ≤49.5%. Mechanistic investigations suggest that thermodynamically the controlled valence band edge position via Rh doping provides a suitable oxidation ability of photogenerated holes, avoiding the powerful hydroxyl radical intermediates prone to overoxidation resulting in high selectivity. Kinetically, oxygen vacancies induced by Rh 3+ substitution in the SrTiO 3 lattice not only favor the dissociative adsorption of alcohols yielding alkoxy species but also induce the weakening of the α-C-H bond facilitating its cleavage by the photogenerated holes. Pt nanoparticles deposited as a cocatalyst contribute to the final hydrogen evolution. © 2019 American Chemical Society.

This work presents a systematic study of the lanthanum tungstate (LaWO) ceramic layers formation on porous metallic substrates as a function of the PS-PVD processing parameters including plasma characteristics, support type and temperature, as well as addition of O2 during the spraying. Through precise control of the PS-PVD parameters, a set of processing conditions were found that led to He gas-tight purely cubic LaWO layers with negligible secondary phase precipitations. Being dependent on process conditioning, the formation and evolution of the cubic La6−xWO12−δ (x = 0.3-0.6) as the main phase of functional importance and of the undesired secondary phases (La2O3 and La6W2O15) was strongly affected by the cation and oxygen stoichiometries. The rapid cooling of the feedstock at particle impact on the substrate led to the formation of highly La-saturated compositions which exhibited significant lattice expansion in comparison with conventionally processed LaWO and is considered beneficial in terms of material performance. And indeed, the H2 permeation performance of the PS-PVD processed LaWO ceramic layers shown earlier by our group was 0.4 ml/min∙cm2 at 825 °C for 60 µm thickness of the functional layer, the highest value reported for this type of proton conducting ceramics, so far. © 2019, ASM International.

A molecular-scale description of water and ice is important in fields as diverse as atmospheric chemistry, astrophysics, and biology. Despite a detailed understanding of water and ice structures on a multitude of surfaces, relatively little is known about the kinetics of water motion on surfaces. Here, we report a detailed study on the diffusion of water monomers and the formation and diffusion of water dimers through a combination of time-lapse low-temperature scanning tunnelling microscopy experiments and first-principles electronic structure calculations on the atomically flat Cu(111) surface. On the basis of an unprecedented long-time study of individual water monomers and dimers over days, we establish rates and mechanisms of water monomer and dimer diffusion. Interestingly, we find that the monomer and the dimer diffusion barriers are similar, despite the significantly larger adsorption energy of the dimer. This is thus a violation of the rule of thumb that relates diffusion barriers to adsorption energies, an effect that arises because of the directional and flexible hydrogen bond within the dimer. This flexibility during diffusion should also be relevant for larger water clusters and other hydrogen-bonded adsorbates. Our study stresses that a molecular-scale understanding of the initial stages of ice nanocluster formation is not possible on the basis of static structure investigations alone. © 2019 American Chemical Society.

Nanostructured carbons with different pore geometries are prepared with a liquid-free nanocasting method. The method uses gases instead of liquid to disperse carbon precursors, leach templates, and remove impurities, minimizing synthetic procedures and the use of chemicals. The method is universal and demonstrated by the synthesis of 12 different porous carbons with various template sources. The effects of pore geometries in catalysis can be isolated and investigated. Two of the resulted materials with different pore geometries are studied as supports for Ru clusters in the hydrogenolysis of 5-hydroxymethylfurfural (HMF) and electrochemical hydrogen evolution (HER). The porous carbon-supported Ru catalysts outperform commercial ones in both reactions. It was found that Ru on bottleneck pore carbon shows a highest yield in hydrogenolysis of HMF to 2,5-dimethylfuran (DMF) due to a better confinement effect. A wide temperature operation window from 110 to 140 °C, with over 75% yield and 98% selectivity of DMF, has been achieved. Tubular pores enable fast charge transfer in electrochemical HER, requiring only 16 mV overpotential to reach current density of 10 mA·cm-2. © 2019 American Chemical Society.

Synthesis of silver nanoparticles (Ag NPs) with state-of-the-art chemical or photo-reduction methods generally takes several steps and requires both reducing agents and stabilizers to obtain NPs with narrow size distribution. Herein, we report a novel method to synthesize Ag NPs rapidly in one step, achieving typical particle sizes in the range from 5 to 15 nm. The synthesis steps only involve three chemicals without any reducing agent: AgNO3 as precursor, polyvinylpyrrolidone (PVP) as stabilizer, and AgCl as photocatalyst. The Ag NPs were supported on carbon and showed excellent performance in thermal catalytic p-nitrophenol reduction and nitrobenzene hydrogenation, and as electrocatalyst for the oxygen reduction reaction. © 2019 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences

Boron-doped diamond (BDD) represents a powerful and innovative electrode material. In particular, in combination with fluorinated solvents such as 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), the system exhibits the largest known electrochemical window of approximately 5 V in protic media. Furthermore, the anodic treatment allows the direct formation of oxyl radicals, which are known to exhibit specific reactivity. The electrochemical dehydrogenative phenol-phenol cross-coupling is a versatile and useful transformation to non-symmetric biphenols. This electro-organic conversion can be divided into two regimes: initial oxidation at the anode and the electrolyte-controlled follow-up reaction. This work intends to provide an answer about the influence of BDD electrodes on oxidation reactions in electrosynthesis. Depending on the electro-organic transformation, the support material of BDD, its boron content, and its fabrication method have a significant influence on the electrosynthetic efficiency. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

H-BiVO 4-x :Mo was successfully deposited on microwire-structured silicon substrates, using indium tin oxide (ITO) as an interlayer and BiOI prepared by electrodeposition as precursor. Electrodeposition of BiOI, induced by the electrochemical reduction of p-benzoquinone, appeared to proceed through three stages, being nucleation of particles at the base and bottom of the microwire arrays, followed by rapid (homogeneous) growth, and termination by increasing interfacial resistances. Variations in charge density and morphology as a function of spacing of the microwires are explained by (a) variations in mass transfer limitations, most likely associated with the electrochemical reduction of p-benzoquinone, and (b) inhomogeneity in ITO deposition. Unexpectedly, H-BiVO 4-x :Mo on microwire substrates (4 μm radius, 4 to 20 μm spacing, and 5 to 16 μm length) underperformed compared to H-BiVO 4-x :Mo on flat surfaces in photocatalytic tests employing sulfite (SO 3 2- ) oxidation in a KPi buffer solution at pH 7.0. While we cannot exclude optical effects, or differences in material properties on the nanoscale, we predominantly attribute this to detrimental diffusion limitations of the redox species within the internal volume of the microwire arrays, in agreement with existing literature and the observations regarding the electrodeposition of BiOI. Our results may assist in developing high-efficiency PEC devices. © Copyright © 2019 American Chemical Society.

Aromatic alcohols are essential components of many solvents, coatings, plasticizers, fine chemicals, and pharmaceuticals. Traditional manufacturing processes involving the oxidation of petroleum-derived aromatic hydrocarbons suffer from low selectivity due to facile overoxidation reactions which produce aromatic aldehydes, acids, and esters. Here we report a Co-containing hydroxyapatite (HAP) catalyst that converts ethanol directly to methylbenzyl alcohols (MB-OH, predominantly 2-MB-OH) at 325 °C. The dehydrogenation of ethanol to acetaldehyde, which is catalyzed by Co2+, has the highest reaction barrier. Acetaldehyde undergoes rapid, HAP-catalyzed condensation and forms the key intermediate, 2-butenal, which yields aromatic aldehydes through self-condensation and then MB-OH via hydrogenation. In the presence of Co2+, 2-butenal is selectively hydrogenated to 2-butenol. This reaction does not hinder aromatization because cross-coupling between 2-butenal and 2-butenol leads directly to MB-OH without passing through MBâ•O. Using these insights a dual-bed catalyst configuration was designed for use in a single reactor to improve the aromatic alcohol selectivity. Its successful use supports the proposed reaction mechanism. Copyright © 2019 American Chemical Society.

Metal-nanoparticles (M-NPs) were synthesized in a wet-chemical synthesis route in tunable aryl alkyl ionic liquids (TAAILs) based on the 1-aryl-3-alkyl-substituted imidazolium motif from Ru3(CO)12 and Ir4(CO)12 by microwave-heating induced thermal decomposition. The size and size dispersion of the NPs were determined by transmission electron microscopy (TEM) to an average diameter of 2.2(±0.1) to 3.9(±0.3) nm for Ru-NPs and to an average diameter of 1.4(±0.1) to 2.4(±0.1) nm for Ir-NPs. The TAAILs used contain the same bis(trifluoromethylsulfonyl)imide anion but differ in the substituents on the 1-aryl ring, e.g. 2-methyl-, 4-methoxy- and 2,4-dimethyl groups and in the 3-alkyl chain lengths (C4H9, C5H11, C8H17, C9H19, C11H23). All used TAAILs are suitable for the stabilization of Ru- and Ir-NPs over months in the IL dispersion. Different from all other investigations on M-NP/IL systems which we are aware of the particle separation properties of the TAAILs vary strongly as a function of the aryl substituent. Good NP separation can be achieved with the 4-methoxyphenyl- and 2,4-dimethylphenyl-substituted ILs, irrespective of the 3-alkyl chain lengths. Significant aggregation can be observed for 2-methylphenyl-substituted ILs. The good NP separation can be correlated with a negative electrostatic potential at the 4-methoxyphenyl or 4-methylphenyl substituent that is in the para-position of the aryl ring, whereas the 2-(ortho-)methylphenyl group assumes no negative potential. ϵ-ePC-SAFT calculations were used to validate that the interactions between ILs and the washing agents (required for TEM analyses) do not cause the observed aggregation/separation behaviour of the M-NPs. Ru-NPs were investigated as catalysts for the solvent-free hydrogenation of benzene to cyclohexane under mild conditions (70 °C, 10 bar) with activities up to 760 (mol cyclohexane) (mol Ru)-1 h-1 and over 95% conversion in ten consecutive runs for Ru-NPs. No significant loss of catalytic activity could be observed. This journal is © The Royal Society of Chemistry.

Electrode selectivity towards hydrogen production is essential in various conversion technologies for renewable energy, as well as in different industrial processes, such as the electrochemical production of sodium chlorate. In this study we present sodium metavanadate as a solution additive, inducing selective cathodic formation of hydrogen in the presence of various other reducible species such as hypochlorite, chlorate, oxygen, nitrate, hydrogen-peroxide and ferricyanide. During electrolysis a vanadium-oxide coating forms from the reduction of sodium metavanadate, explaining the observed enhanced selectivity. The hydrogen evolution reaction proceeds without significantly altered kinetics on such in situ modified electrode surfaces. This suggests that the reaction takes place at the interface between the electrode surface and the protective film, which acts as a diffusion barrier preventing the unwanted species to reach the electrode surface. © 2018 The Authors

The effect of hydrogen atoms at grain boundaries in metals is usually detrimental to the cohesion of the interface. This effect can be quantified in terms of the strengthening energy, which is obtained following the thermodynamic model of Rice and Wang. A critical component of this model is the bonding or solution energy of the atoms to the free surfaces that are created during decohesion. At a grain boundary in a multicomponent system, it is not immediately clear how the different species would partition and distribute on the cleaved free surfaces. In this work, it is demonstrated that the choice of partitioning pattern has a significant effect on the predicted influence of H and C on grain boundary cohesion. To this end, the ∑3(112)[110] symmetric tilt grain boundary in bcc Fe with different contents of interstitial C and H was studied, taking into account all possible distributions of the elements, as well as surface diffusion effects. H as a single element has a negative influence on grain boundary cohesion, independent of the details of the H distribution. C, on the other hand, can act both ways, enhancing or reducing the cohesion of the interface. The effect of mixed H and C compositions depends on the partition pattern. However, the general trend is that the number of detrimental cases increases with increasing H content. A decomposition of the strengthening energy into chemical and mechanical contributions shows that the elastic contribution dominates at high C contents, while the chemical contribution sets the trend for high H contents. © 2019 by the authors.

The efficient reduction of protons by non-noble metals under mild conditions is a challenge for our modern society. Nature utilises hydrogenases, enzymatic machineries that comprise iron- and nickel- containing active sites, to perform the conversion of protons to hydrogen. We herein report a straightforward synthetic pathway towards well-defined particles of the bio-inspired material FexNi9-xS8, a structural and functional analogue of hydrogenase metal sulfur clusters. Moreover, the potential of pentlandites to serve as photocatalysts for solar-driven H2-production is assessed for the first time. The FexNi9-xS8 materials are visible light responsive (band gaps between 2.02 and 2.49 eV, depending on the pentlandite's Fe:Ni content) and display a conduction band energy close to the thermodynamic potential for proton reduction. Despite the limited driving force, a modest activity for photocatalytic H2 has been observed. Our observations show the potential for the future development of pentlandites as photocatalysts. This work provides a basis to explore powerful synergies between biomimetic chemistry and material design to unlock novel applications in solar energy conversion. © 2019 The Royal Society of Chemistry.

Unraveling the atomistic details of solid/liquid interfaces, e.g., by means of vibrational spectroscopy, is of vital importance in numerous applications, from electrochemistry to heterogeneous catalysis. Water-oxide interfaces represent a formidable challenge because a large variety of molecular and dissociated water species are present at the surface. Here, we present a comprehensive theoretical analysis of the anharmonic OH stretching vibrations at the water/ZnO(1010) interface as a prototypical case. Molecular dynamics simulations employing a reactive high-dimensional neural network potential based on density functional theory calculations have been used to sample the interfacial structures. In the second step, one-dimensional potential energy curves have been generated for a large number of configurations to solve the nuclear Schrödinger equation. We find that (i) the ZnO surface gives rise to OH frequency shifts up to a distance of about 4 Å from the surface; (ii) the spectrum contains a number of overlapping signals arising from different chemical species, with the frequencies decreasing in the order ν(adsorbed hydroxide) > ν(non-adsorbed water) > ν(surface hydroxide) > ν(adsorbed water); (iii) stretching frequencies are strongly influenced by the hydrogen bond pattern of these interfacial species. Finally, we have been able to identify substantial correlations between the stretching frequencies and hydrogen bond lengths for all species. © 2018 Author(s).

Oxygenic photosynthetic organisms perform solar energy conversion of water and CO2 to O2 and sugar at a broad range of wavelengths and light intensities. These cells also metabolize sugars using a respiratory system that functionally overlaps the photosynthetic apparatus. In this study, we describe the harvesting of photocurrent used for hydrogen production from live cyanobacteria. A non-harmful gentle physical treatment of the cyanobacterial cells enables light-driven electron transfer by an endogenous mediator to a graphite electrode in a bio-photoelectrochemical cell, without the addition of sacrificial electron donors or acceptors. We show that the photocurrent is derived from photosystem I and that the electrons originate from carbohydrates digested by the respiratory system. Finally, the current is utilized for hydrogen evolution on the cathode at a bias of 0.65 V. Taken together, we present a bio-photoelectrochemical system where live cyanobacteria produce stable photocurrent that can generate hydrogen. © 2018 The Author(s).

Hydrogen reduction of TiO2 to generate surface Ti3+ can significantly increase the photochemical activity under solar-light illumination. However, the low surface areas of commercial TiO2 limit their photocatalytic activities. Herein, we report a high surface area ordered mesoporous black TiO2, which exhibits an improved photocatalytic performance. The TiO2 material was prepared by using a highly ordered mesoporous carbon CMK-3 as a hard template, which possesses very high surface area, large pore volume and uniform mesopores. By using the advantage of pore confinement in the mesoporous carbon template, TiO2-carbon composites were annealed at different temperatures to investigate the influence of the crystallinity of TiO2 on the photocatalytic hydrogen production. TiO2 calcined at 500 °C, having a high surface area (up to 158 m2 g−1), large pore volume (up to 0.62 cm3 g−1), uniform pore size (5–6 nm), and anatase crystal structure, indicated the highest hydrogen generation rate. Since the TiO2 has been treated at a higher temperature in the confinement of the mesoporous carbon, the TiO2 can easily be reduced at 500 °C under hydrogen atmosphere to generate surface Ti3+ species without destruction of the mesostructure and exhibits a high solar-driven hydrogen evolution rate (188 μmol h−1), which is more than two times higher than that of commercial TiO2 (82 μmol h−1). © 2018 Elsevier Inc.

For the growth of 2D transition metal dichalcogenides, such as molybdenum (MoS2) and tungsten disulfides (WS2), metalorganic chemical vapor deposition (MOCVD) routes are favorable due to their superior scalability, the possibility to tune the processing temperatures by a proper choice of reactants thus avoiding the need for a postdeposition treatment. Herein, the first example of a promising MOCVD route for the direct fabrication of MoS2 and WS2 layers under moderate process conditions is reported. This straightforward route is successfully realized by the combination of metalorganic precursors of Mo or W bearing the amidinato ligand with just elemental sulfur. The formation of stoichiometric hexagonal 2H-MoS2 and 2H-WS2 is demonstrated which is confirmed by Raman, X-ray diffraction, and X-ray photoelectron spectroscopy studies. The deposited layers are evaluated for their electrocatalytic activity in hydrogen evolution reaction as a proof of principle for application in water splitting devices. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Nuclear quantum effects (NQEs) cause the nuclei of light elements like hydrogen to delocalize, affecting numerous properties of water and aqueous solutions, such as hydrogen-bonding and proton transfer barriers. Here, we address the prototypical case of aqueous NaOH solutions by investigating the effects of quantum nuclear fluctuations on radial distribution functions, hydrogen-bonding geometries, power spectra, proton transfer barriers, proton transfer rates, water self-exchange rates around the Na+ cations, and diffusion coefficients, for the full room-temperature solubility range. These properties were calculated from classical and ring-polymer molecular dynamics simulations employing a reactive high-dimensional neural network potential based on dispersion-corrected density functional theory reference calculations. We find that NQEs have a very small impact on the solvation structure around Na+, slightly strengthen the water-water and water-hydroxide hydrogen bonds, and lower the peak positions in the power spectra for the HOH bending and OH stretching modes by about 50 and 100 cm-1, respectively. Moreover, NQEs significantly lower the proton transfer barriers, thus increasing the proton transfer rates, resulting in an increase of the diffusion coefficient in particular of OH-, as well as a decrease of the mean residence time of molecules in the first hydration shell around Na+ at high NaOH concentrations. © 2018 American Chemical Society.

We present a transparent and flexible self-charging biosupercapacitor based on an optimised mediator- and membrane-free enzymatic glucose/oxygen biofuel cell. Indium tin oxide (ITO) nanoparticles were spray-coated on transparent conducting ITO supports resulting in a flocculent, porous and nanostructured electrode surface. By this, high capacitive currents caused by an increased electrochemical double layer as well as enhanced catalytic currents due to a higher number of immobilised enzyme molecules were obtained. After a chemical pre-treatment with a silane derivative, bilirubin oxidase from Myrothecium verrucaria was immobilized onto the ITO nanostructured electrode surface under formation of a biocathode, while bioanodes were obtained by either immobilisation of cellobiose dehydrogenase from Corynascus thermophilus or soluble PQQ-dependent glucose dehydrogenase from Acinetobacter calcoaceticus. The latter showed a lower apparent KM value for glucose conversion and higher catalytic currents at µM glucose concentrations. Applying the optimised device as a biosupercapacitor in a discontinuous charge/discharge mode led to a generated power output of 0.030 mW/cm2 at 50 µM glucose, simulating the glucose concentration in human tears. This represents an enhancement by a factor of 350 compared to the power density obtained from the continuously operating biofuel cell with a maximum power output of 0.086 µW/cm2 under the same conditions. After 17 h of charging/discharging cycles a remarkable current enhancement was still measured. The entire device was transferred to flexible materials and applied for powering a flexible display showing its potential applicability as an intermittent power source in smart contact lenses. © 2017 Elsevier B.V.

In this work we present a viologen-modified electrode providing protection for hydrogenases against high potential inactivation. Hydrogenases, including O2-tolerant classes, suffer from reversible inactivation upon applying high potentials, which limits their use in biofuel cells to certain conditions. Our previously reported protection strategy based on the integration of hydrogenase into redox matrices enabled the use of these biocatalysts in biofuel cells even under anode limiting conditions. However, mediated catalysis required application of an overpotential to drive the reaction, and this translates into a power loss in a biofuel cell. In the present work, the enzyme is adsorbed on top of a covalently-attached viologen layer which leads to mixed, direct and mediated, electron transfer processes; at low overpotentials, the direct electron transfer process generates a catalytic current, while the mediated electron transfer through the viologens at higher potentials generates a redox buffer that prevents oxidative inactivation of the enzyme. Consequently, the enzyme starts the catalysis at no overpotential with viologen self-activated protection at high potentials. © The Royal Society of Chemistry.

The Ni(P2N2)2 catalysts are among the most efficient non-noble-metal based molecular catalysts for H2 cycling. However, these catalysts are O2 sensitive and lack long term stability under operating conditions. Here, we show that in a redox silent polymer matrix the catalyst is dispersed into two functionally different reaction layers. Close to the electrode surface is the "active" layer where the catalyst oxidizes H2 and exchanges electrons with the electrode generating a current. At the outer film boundary, insulation of the catalyst from the electrode forms a "protection" layer in which H2 is used by the catalyst to convert O2 to H2O, thereby providing the "active" layer with a barrier against O2. This simple but efficient polymer-based electrode design solves one of the biggest limitations of these otherwise very efficient catalysts enhancing its stability for catalytic H2 oxidation as well as O2 tolerance. © 2018 The Author(s).

The scope of this research project covers the examination of the microstructure of different austenitic steels with regard to H embrittlement. It is known from the literature that the alloy X2CrNi18-9 is susceptible to H embrittlement, whereas steel X2CrNiMo18-14-3 is highly resistant to the embrittlement process. Austenitic steels with a low γ stability are susceptible to form α' martensite during plastic deformation. The γ stability can be estimated using empirical formulas, while one drawback of this approach is that only a limited amount of alloying elements is considered by those equations. A thermodynamic approach has proven effective for the estimation of the γ stability of multicomponent alloys. Hence, results from the microsegregation analysis for alloy X2CrNi18 - 9 using energy dispersive X-ray spectroscopy are presented and their influence on the local γ stability is discussed based on property distribution images. © 2018 Carl Hanser Verlag, München.

Sodium dichromate is an essential solution additive for the electrocatalytic production of sodium chlorate, assuring selective hydrogen evolution. Unfortunately, the serious environmental and health concerns related to hexavalent chromium mean there is an urgent need to find an alternative solution to achieve the required selectivity. In this study sodium permanganate is evaluated as a possible alternative to chromate, with positive results. The permanganate additive is stable in hypochlorite-containing solutions, and during electrolysis a thin film is reductively deposited on the cathode. The deposit is identified as amorphous manganese oxide by Raman spectroscopic and X-ray diffraction studies. Using different electrochemical techniques (potentiodynamic measurements, galvanostatic polarization curves) we demonstrate that the reduction of hypochlorite is suppressed, while the hydrogen evolution reaction can still proceed. In addition, the formed manganese oxide film acts as a barrier for the reduction of dissolved oxygen. The extent of hydrogen evolution selectivity in hypochlorite solutions was quantified in an undivided electrochemical cell using mass spectrometry. The cathodic current efficiency is significantly enhanced after the addition of permanganate, while the effect on the anodic selectivity and the decomposition of hypochlorite in solution is negligible. Importantly, similar results were obtained using electrodes with manganese oxide films formed ex situ. In conclusion, manganese oxides show great promise in inducing selective hydrogen evolution, and may open new research avenues to the rational design of selective cathodes, both for the chlorate process and for related processes such as photocatalytic water splitting. © 2018 Elsevier Ltd

Interfacing photosynthetic proteins specifically photosystem 1 (PS1) with electrodes enables light-induced charge separation processes for powering semiartificial photobiodevices with, however, limited long-term stability. Here, we present the in-depth evaluation of a PS1/Os-complex-modified redox polymer-based biocathode by means of scanning photoelectrochemical microscopy. Focalized local illumination of the bioelectrode and concomitant collection of H2O2 at the closely positioned microelectrode provide evidence for the formation of partially reduced oxygen species under light conditions. Long-term evaluation of the photocathode at different O2 concentrations as well as after incorporating catalase and superoxide dismutase reveals the particularly challenging issue of avoiding the generation of reactive species. Moreover, the evaluation of films prepared with inactivated PS1 and free chlorophyll points out additional possible pathways for the generation of oxygen radicals. To avoid degradation of PS1 during illumination and hence to enhance the long-term stability, the operation of biophotocathodes under anaerobic conditions is indispensable. © 2018 The Author(s).

Hydrogen is one of the most promising alternatives for fossil fuels. However, the power output of hydrogen/oxygen fuel cells is often restricted by mass transport limitations of the substrate. Here, we present a dual-gas breathing H2/air biofuel cell that overcomes these limitations. The cell is equipped with a hydrogen-oxidizing redox polymer/hydrogenase gas-breathing bioanode and an oxygen-reducing bilirubin oxidase gas-breathing biocathode (operated in a direct electron transfer regime). The bioanode consists of a two layer system with a redox polymer-based adhesion layer and an active, redox polymer/hydrogenase top layer. The redox polymers protect the biocatalyst from high potentials and oxygen damage. The bioanodes show remarkable current densities of up to 8 mA cm-2. A maximum power density of 3.6 mW cm-2 at 0.7 V and an open circuit voltage of up to 1.13 V were achieved in biofuel cell tests, representing outstanding values for a device that is based on a redox polymer-based hydrogenase bioanode. © 2018, The Author(s).

A key issue in understanding and effectively managing hydrogen embrittlement in complex alloys is identifying and exploiting the critical role of the various defects involved. A chemo-mechanical model for hydrogen diffusion is developed taking into account stress gradients in the material, as well as microstructural trapping sites such as grain boundaries and dislocations. In particular, the energetic parameters used in this coupled approach are determined from ab initio calculations. Complementary experimental investigations that are presented show that a numerical approach capable of massive scale-bridging up to the macroscale is required. Due to the wide range of length scales accounted for, we apply homogenisation schemes for the hydrogen concentration to reach simulation dimensions comparable to metallurgical process scales. Via a representative volume element approach, an ab initio based scale bridging description of dislocation-induced hydrogen aggregation is easily accessible. When we extend the representative volume approach to also include an analytical approximation for the ab initio based description of grain boundaries, we find conceptual limitations that hinder a quantitative comparison to experimental data in the current stage. Based on this understanding, the development of improved strategies for further efficient scale bridging approaches is foreseen. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.

In high-strength carbon steels suitable for use in the automotive industry, hydrogen embrittlement (HE) is a potential barrier to the widespread application of these materials. The behaviour of hydrogen within the most prevalent carbide, namely cementite, has been investigated via ab initio simulation. In order to examine possible decohesion effects of hydrogen on carbon steels, the binding and diffusion of hydrogen at the interface between ferrite and cementite has been examined. In order to understand the effect of hydrogen on the mechanical properties of carbon steels, simulated ab initio tensile tests have been performed on the ferrite-cementite bicrystal. The results of the tensile tests can be combined with thermodynamic considerations in order to obtain the expected hydrogen concentrations at such ferrite-cementite phase boundaries. We find that the effect of hydrogen on the cohesion of the phase boundary may be significant, even when the bulk hydrogen concentration is low. © 2018 Acta Materialia Inc.

The dehydrogenation of ethanol to acetaldehyde (DHEA) is an environmentally benign alternative for synthetic chemistry and for the fine chemical industry. The key is to design Cu-based catalysts with certain structures to obtain high acetaldehyde selectivity. Herein, hybrid C@SiO2 hollow submicron spheres were designed and synthesized using a confined pyrolysis method. This hybrid structure processes a layer of carbon-silica hybrid shell. After loading the Cu, the Cu/C@SiO2 catalyst exhibited 36.1% conversion of ethanol and ∼99% acetaldehyde selectivity at 260 °C. The hybrid support combined the two favorable properties of carbon and silica and thus improving both selectivity and stability. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Hydrogenases with Ni- and/or Fe-based active sites are highly active hydrogen oxidation catalysts with activities similar to those of noble metal catalysts. However, the activity is connected to a sensitivity towards high-potential deactivation and oxygen damage. Here we report a fully protected polymer multilayer/hydrogenase-based bioanode in which the sensitive hydrogen oxidation catalyst is protected from high-potential deactivation and from oxygen damage by using a polymer multilayer architecture. The active catalyst is embedded in a low-potential polymer (protection from high-potential deactivation) and covered with a polymer-supported bienzymatic oxygen removal system. In contrast to previously reported polymer-based protection systems, the proposed strategy fully decouples the hydrogenase reaction form the protection process. Incorporation of the bioanode into a hydrogen/glucose biofuel cell provides a benchmark open circuit voltage of 1.15 V and power densities of up to 530 µW cm−2 at 0.85 V. © 2018, The Author(s).

The activity towards the oxygen reduction reaction (ORR) of single silver nanoparticles (AgNP) was quantified by using AgNP impacts on dual-bore carbon nanoelectrodes in highly alkaline media. We found suitable conditions for the particles to adhere sufficiently stably for detailed electrochemical characterization of a single particle. The special electrode design opens the possibility to dose gaseous oxygen to the nanoparticle under study. Deactivation of the catalytic activity of the AgNP upon excessive exposure to oxygen as well as the recovery of catalytic activity under reducing conditions is presumably attributed to hydrogen evolution at the applied low potentials. The proposed approach allows mechanistic parameters for the ORR to be extracted at a single AgNP in highly alkaline media in the absence of any binder materials and under exclusion of averaging ensemble effects. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

The functional coupling of photoactive nanostructures with enzymes creates a strategy for the design of light-triggered biocatalysts. This study highlights the efficient wiring of flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase (FAD-GDH) to PbS quantum dot (QD)-sensitized inverse opal TiO2 electrodes (IO-TiO2) by means of an Os-complex-containing redox polymer for the light-driven glucose oxidation. For the construction of IO-TiO2 scaffolds, a template approach has been developed, enabling the tunability of the surface area and a high loading capacity for the integration of QDs, redox polymer, and enzyme. The biohybrid signal chain can be switched on with light, generating charge carriers within the QDs, triggering a multistep electron-transfer cascade from the enzyme toward the redox polymer via the QDs and finally to the IO-TiO2 electrode. The resulting anodic photocurrent can be modulated by the potential, the excitation intensity, and the glucose concentration, providing a new degree of freedom for the control of biocatalyic reactions at electrode interfaces. Maximum photocurrents of 207 μA cm-2 have been achieved in the presence of glucose, and a first gain of electrons from the biocatalytic reaction is found at -540 mV vs Ag/AgCl, 1 M KCl, which lowers the working potential by >500 mV as compared to light-insensitive electrodes. The biohybrid system combines the advantages of a high surface area of IO films, an efficient charge-carrier generation and separation at the QDs/TiO2 interface, and an efficient wiring of FAD-GDH to the QDs via a redox polymer, resulting in photo(bio)anodes of high performance for sensing and power supply. © 2018 American Chemical Society.

Mössbauerite is investigated for the first time as an “iron-only” mineral for the electrocatalytic oxygen evolution reaction in alkaline media. The synthesis proceeds via intermediate mixed-valence green rust that is rapidly oxidized in situ while conserving the layered double hydroxide structure. The material catalyzes the oxygen evolution reaction on a glassy carbon electrode with a current density of 10 mA cm−2 at 1.63 V versus the reversible hydrogen electrode. Stability measurements, as well as post-electrolysis characterization are presented. This work demonstrates the applicability of iron-only layered double hydroxides as earth-abundant oxygen evolution electrocatalysts. Mössbauerite is of fundamental importance since as an all Fe3+ material its performance has no contributions from unknown synergistic effects as encountered for mixed valence Co/Ni/Fe LDH. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Ti and its alloys have a high affinity for hydrogen and are typical hydride formers. Ti-hydride are brittle phases which probably cause premature failure of Ti-alloys. Here, we used atom probe tomography and electron microscopy to investigate the hydrogen distribution in a set of specimens of commercially pure Ti, model and commercial Ti-alloys. Although likely partly introduced during specimen preparation with the focused-ion beam, we show formation of Ti-hydrides along α grain boundaries and α/β phase boundaries in commercial pure Ti and α+β binary model alloys. No hydrides are observed in the α phase in alloys with Al addition or quenched-in Mo supersaturation. © 2018 Acta Materialia Inc.

We report a designed Cu/C/SiO2 composite catalyst, which shows a high acetaldehyde selectivity (up to ∼98%) and good stability for a 60 h test at 260 °C in ethanol dehydrogenation. Various characterization techniques demonstrate that the carbon covers the Si-OH groups on silica and promotes the reduction of Cu+ to Cu0. This reduces the concentration of active sites for secondary reactions of CH3CHO, which leads to a high initial selectivity (∼93%) as compared to that of Cu/SiO2 (∼76%). Moreover, the chemical interaction between Cu and SiO2 of the C/SiO2 support, verified by X-ray photoelectron spectroscopy, enhances the interaction between the metal and the support and thus contributes to prevention of the agglomeration of Cu particles, which is the reason for the good catalytic stability of Cu/C/SiO2. Thus, this study is an example of how careful design of the catalyst can strongly improve the catalytic performance. © 2018 The Royal Society of Chemistry.

Hydrogen is increasingly considered as fuel for future mobility or for stationary applications. However, the safe distribution and storage of pure hydrogen is only possible with suitable materials. Interstitially dissolved hydrogen atoms in the lattice of numerous metals are responsible for hydrogen embrittlement (HE). If hydrogen is introduced by an external source, it is called hydrogen environment embrittlement (HEE). Commonly, steels like AISI 316L with a high resistance to HEE include a large number of alloying elements and in high amount. High alloying levels result in a decrease of cost-efficiency. Therefore, the systematic investigation of lean-alloyed austenitic stainless steels is necessary in order to understand the mechanism of HEE. For that purpose, the steel grades AISI 304L and AISI 316L are selected in this work. Tensile tests in air and 400 bar hydrogen gas atmospheres are performed. After tensile testing in H, AISI 304L revealed secondary cracks at the specimen surface, which are related to the local austenite stability, which in turn is affected by the level of micro-segregation. The microstructural investigations of the crack environment directly contribute to the understanding of the micro-mechanisms of HEE. Property-maps generated from experimentally measured distributions of alloying elements allow to correlate the impact of micro-segregations on the local austenite stability. It is shown, that local segregation-bands affect the initiation and propagation of secondary cracks. In this context, the local austenite stability which is significantly affected by the Ni distribution will be discussed in detail by comparison of the metastable austenitic steel grades AISI 304L and AISI 316L. © 2018 Trans Tech Publications, Switzerland.

The design of non-noble metal-containing heterogeneous catalysts for the activation of small molecules is of utmost importance for our society. While nature possesses very sophisticated machineries to perform such conversions, rationally designed catalytic materials are rare. Herein, we aim to raise the awareness of the overall common design and working principles of catalysts incorporating aspects of biology, chemistry, and material sciences. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

[FeFe]-Hydrogenases are the most efficient enzymes for catalytic hydrogen turnover. Their H2 production efficiency is hitherto unrivalled. However, functional details of the catalytic machinery and possible modes of application are discussed controversially. The incorporation of synthetically modified cofactors and utilization of semi-artificial enzymes only recently allowed us to shed light on key steps of the catalytic cycle. Herein, we summarize the essential findings regarding the redox chemistry of [FeFe]-hydrogenases and discuss their catalytic hydrogen turnover. We furthermore will give an outlook on potential research activities and exploit the utilization of synthetic cofactor mimics. © 2018 The Royal Society of Chemistry.

The unmatched catalytic turnover rates of [FeFe]-hydrogenases require an exceptionally efficient proton-transfer (PT) pathway to shuttle protons as substrates or products between bulk water and catalytic center. For clostridial [FeFe]-hydrogenase CpI such a pathway has been proposed and analyzed, but mainly on a theoretical basis. Here, eleven enzyme variants of two different [FeFe]-hydrogenases (CpI and HydA1) with substitutions in the presumptive PT-pathway are examined kinetically, spectroscopically, and crystallographically to provide solid experimental proof for its role in hydrogen-turnover. Targeting key residues of the PT-pathway by site directed mutagenesis significantly alters the pH-activity profile of these variants and in presence of H2 their cofactor is trapped in an intermediate state indicative of precluded proton-transfer. Furthermore, crystal structures coherently explain the individual levels of residual activity, demonstrating e.g. how trapped H2O molecules rescue the interrupted PT-pathway. These features provide conclusive evidence that the targeted positions are indeed vital for catalytic proton-transfer. © 2018, The Author(s).

The oxidation and stability of multi-walled carbon nanotubes (CNTs) have been investigated by exposing CNTs in 30% w/v H2O2 solution at room temperature (RT) for up to 8 weeks and at 80 °C for up to 8 h. H2O2 oxidation not only generated surface oxygen-containing groups, but also created surface defects, as disclosed by results of temperature-programmed desorption and X-ray Photoelectron Spectroscopy. The total surface oxygen content was found to be correlated to the final H2O2 concentration. The higher the total surface oxygen content on CNTs, the lower the final H2O2 concentration. Meanwhile, the carbon oxidation and simultaneous H2O2 decomposition were observed and confirmed by an online analysis of evolved gases during the oxidation stepwise heated from room temperature to 80 °C. Raman study showed that the D/G and D'/G ratios of the CNTs oxidized at RT first decreased with an oxidation time of 4 weeks and then increased when prolonging the oxidation time up to 8 weeks. Similar trend was also observed on the CNTs oxidized at 80 °C. The size of CNTs was gradually reduced with increasing oxidation time as shown by SEM studies. Our work reveals the critical changes in the surface oxygen groups as well as the changes in morphology at two distinct stages of hydrogen peroxide treatment, purification and then functionalization. CNTs can withstand 30% w/v H2O2 oxidation for only a certain time, while they may be damaged or consumed eventually in long-term applications. Our study contributes to filling in the knowledge gap about CNT surface oxidation and structural changes with H2O2 treatment under industrial conditions. © 2018 Elsevier B.V.

Hydrogen exposure has been found to result in metal embrittlement. In this work, we use nanoindentation to study the mechanical properties of polycrystalline tungsten subjected to deuterium plasma exposure. For the purpose of comparison, nanoindentation tests on exposed and unexposed reference tungsten were carried out. The results exhibit a decrease in the pop-in load and an increase in hardness on the exposed tungsten sample after deuterium exposure. No significant influence of grain orientation on the pop-in load was observed. After a desorption time of td ≥ 168 h, both the pop-in load and hardness exhibit a recovering trend toward the reference state without deuterium exposure. The decrease of pop-in load is explained using the defactant theory, which suggests that the presence of deuterium facilitates the dislocation nucleation. The increase of hardness is discussed based on two possible mechanisms of the defactant theory and hydrogen pinning of dislocations. © 2018 Materials Research Society.

The transport behavior of hydrogen in ultra-high strength steel grades (UHSS) has been analyzed by several test and evaluation methods. In particular, permeation and desorption measurements have been performed to evaluate material specific parameters such as the effective diffusion coefficient, the reversible trap density and the reversible trap activation energy. Subjects of this study were a dual phase steel grade (DP) with a ferritic-martensitic microstructure and a martensitic steel grade (MS). The results of the permeation measurements indicate that the influence of irreversible traps might be negligible for the investigated UHSS compared to other impact factors. The evaluated reversible trap densities were some orders of magnitude higher than those known for pure iron reflecting the more complex microstructure. The major influence on hydrogen trapping is attributed to reversible traps like grain boundaries and dislocations based on the results of desorption measurements. © 2018 Elsevier B.V.

We investigated the hydrogen embrittlement mechanism in an interstitially carbon alloyed equimolar CoCrFeMnNi high-entropy alloy (HEA) through low strain rate tensile testing under in-situ hydrogen charging. The tensile ductility was significantly reduced by hydrogen charging. The failure mode of the interstitial HEA in presence of hydrogen was a combination of intergranular and transgranular fracture as well as microvoid coalescence. Aggregated nano-carbides act as potential sites for crack initiation. These findings show that the carbon alloyed equimolar high-entropy alloy is susceptible to hydrogen embrittlement. © 2018 Elsevier Ltd

Tungsten carbide has attracted much interest as possible support for oxygen reduction and hydrogen oxidation in fuel cells and as catalyst itself for the hydrogen evolution reaction in water electrolyzers in the last years. Herein, we investigate the dissolution behavior of hexagonal tungsten carbide in acidic media with cyclovoltammetric and galvanostatic procedures under steady-state and dynamic conditions. The tungsten dissolution rate in the electrolyte was monitored in-situ and time resolved via coupling of the scanning flow cell with an inductively coupled plasma mass spectrometer (SFC-ICP-MS), allowing a direct correlation of potential and amount of dissolved species. The stability and passivation behavior of tungsten carbide was compared to pristine tungsten metal and its highest oxide WO3 in fuel cell/electrolyzer relevant potential ranges. It was found that partial passivation in the oxygen reduction region takes place, accompanied by steady dissolution of tungsten slightly above these potentials. In the HER/HOR region, no significant dissolution was observed. The dissolution rate of WC at high potentials was found to be in many cases almost one order of magnitude lower than for the pristine metal, yet two orders of magnitude higher than for its corresponding highest oxide. © 2018 Elsevier Ltd

Combining concepts of semiconductor physics and corrosion science, we develop a novel approach that allows us to perform ab initio calculations under controlled potentiostat conditions for electrochemical systems. The proposed approach can be straightforwardly applied in standard density functional theory codes. To demonstrate the performance and the opportunities opened by this approach, we study the chemical reactions that take place during initial corrosion at the water-Mg interface under anodic polarization. Based on this insight, we derive an atomistic model that explains the origin of the anodic hydrogen evolution. © 2018 American Physical Society.

[FeFe]-hydrogenases are superior hydrogen conversion catalysts. They bind a cofactor (H-cluster) comprising a four-iron and a diiron unit with three carbon monoxide (CO) and two cyanide (CN−) ligands. Hydrogen (H2) and oxygen (O2) binding at the H-cluster was studied in the C169A variant of [FeFe]-hydrogenase HYDA1, in comparison to the active oxidized (Hox) and CO-inhibited (Hox-CO) species in wildtype enzyme. 57Fe labeling of the diiron site was achieved by in vitro maturation with a synthetic cofactor analogue. Site-selective X-ray absorption, emission, and nuclear inelastic/forward scattering methods and infrared spectroscopy were combined with quantum chemical calculations to determine the molecular and electronic structure and vibrational dynamics of detected cofactor species. Hox reveals an apical vacancy at Fed in a [4Fe4S-2Fe]3 − complex with the net spin on Fed whereas Hox-CO shows an apical CN− at Fed in a [4Fe4S-2Fe(CO)]3 − complex with net spin sharing among Fep and Fed (proximal or distal iron ions in [2Fe]). At ambient O2 pressure, a novel H-cluster species (Hox-O2) accumulated in C169A, assigned to a [4Fe4S-2Fe(O2)]3 − complex with an apical superoxide (O2 −) carrying the net spin bound at Fed. H2 exposure populated the two-electron reduced Hhyd species in C169A, assigned as a [(H)4Fe4S-2Fe(H)]3 − complex with the net spin on the reduced cubane, an apical hydride at Fed, and a proton at a cysteine ligand. Hox-O2 and Hhyd are stabilized by impaired O2 – protonation or proton release after H2 cleavage due to interruption of the proton path towards and out of the active site. © 2017

The study is focused on Ni-ion release rates from NiTi surfaces exposed in the cell culture media and human vascular endothelial cell (HUVEC) culture environments. The NiTi surface layers situated in the depth of 70 μm below a NiTi oxide scale are affected by interactions between the NiTi alloys and the bio-environments. The finding was proved with use of inductively coupled plasma mass spectrometry and electron microscopy experiments. As the exclusive factor controlling the Ni-ion release rates was not only thicknesses of the oxide scale, but also the passivation depth, which was two-fold larger. Our experimental data strongly suggested that some other factors, in addition to the Ni concentration in the oxide scale, admittedly hydrogen soaking deep below the oxide scale, must be taken into account in order to rationalize the concentrations of Ni-ions released into the bio-environments. The suggested role of hydrogen as the surface passivation agent is also in line with the fact that the Ni-ion release rates considerably decrease in NiTi samples that were annealed in controlled hydrogen atmospheres prior to bio-environmental exposures. © 2017 Elsevier B.V.

The performance of electrolyzers for hydrogen production is strongly influenced by electrolyte impurities having either a positive or negative impact on the activity of electrocatalysts. We show that cathode deactivation by zinc impurities present in the electrolyte can be overcome by employing catalyst immobilization based on self-assembled and self-healing films. During electrolysis zinc impurities deposit as dendritic films on the cathode electrode increasing the overpotential for the hydrogen evolution reaction (HER), however, continuous self-assembling and self-healing of HER catalyst films subsequently mask the zinc dendrites restoring the advantageous HER overpotential. Zn electrolyte impurities are turned from having a negative to a positive impact leading to an enhanced performance of the cathode due to the increase in surface area caused by the growth of the Zn dendrites. © 2018 Elsevier Ltd

Spillover hydrogen species were generated by dissociative H2 adsorption on Pt nanoparticles supported on nitrogen-doped mesoporous carbon. The spillover hydrogen species on the support can migrate back to the Pt nanoparticles and hydrogenate subsequently adsorbed nitrobenzene to aniline at 80 °C, which was detected during temperature-programmed desorption experiments from 80 to 300 °C in pure He. The amount of spillover hydrogen can be tuned mainly by the pre-reduction temperature rather than by other parameters. The absence of aniline formation during nitrobenzene desorption experiments in the presence of CO indicates that hydrogenation occurs exclusively on Pt and that the spillover hydrogen species are present on the carbon support in a chemically inactive state. Most likely, spillover hydrogen is reversibly stored on the carbon support as adsorbed protons on the surface and as electrons in the bulk. These findings provide a new perspective on Pt/C-based hydrogen storage materials and fuel cell catalysts. © 2018

A concept for amperometric detection and quantification of H2 employing a palladium microsensor is demonstrated. Resistive sensors exploit the outstanding affinity of Pd toward H2 absorption leading to a detectable modulation in resistivity, while amperometric sensors are generally non-Pd-based and detect the electrochemical oxidation of H2 at the electrode surface. The latter method requires the use of a porous membrane in order to ensure that the electrode reaction is limited by the diffusion of H2 from the gas phase to the sensing electrode. We introduce direct quantification of dissolved H2 in aqueous electrolytes that relies on a pre-concentration mechanism at Pd modified microelectrodes and the subsequent amperometric or coulometric oxidation of H2 from bulk Pd. Due to the straightforward data analysis, this method allows for precise determination of H2 concentration in solution, with the maximum sensitivity obtained by adjusting the pre-concentration time. © 2017 Elsevier B.V.

Heteroleptic bis(tert-butylimido)bis(N,N′-diisopropylacetamidinato) compounds of molybdenum and tungsten are introduced as precursors for atomic layer deposition of tungsten and molybdenum oxide thin films using ozone as the oxygen source. Both precursors have similar thermal properties but exhibit different growth behaviors. With the molybdenum precursor, high growth rates up to 2 Å/cycle at 300 °C and extremely uniform films are obtained, although the surface reactions are not completely saturative. The corresponding tungsten precursor enables saturative film growth with a lower growth rate of 0.45 Å/cycle at 300 °C. Highly pure films of both metal oxides are deposited, and their phase as well as stoichiometry can be tuned by changing the deposition conditions. The WOx films crystallize as γ-WO3 at 300 °C and above, whereas the films deposited at lower temperatures are amorphous. Molybdenum oxide can be deposited as either amorphous (≤250 °C), crystalline suboxide (275 °C), a mixture of suboxide and α-MoO3 (300 °C), or pure α-MoO3 (≥325 °C) films. MoOx films are further characterized by synchrotron photoemission spectroscopy and temperature-dependent resistivity measurements. A suboxide MoOx film deposited at 275 °C is demonstrated to serve as an efficient hydrogen gas sensor at a low operating temperature of 120 °C. © 2018 American Chemical Society.

The [FeFe]-hydrogenases of bacteria and algae are the most efficient hydrogen conversion catalysts in nature. Their active-site cofactor (H-cluster) comprises a [4Fe-4S] cluster linked to a unique diiron site that binds three carbon monoxide (CO) and two cyanide (CN-) ligands. Understanding microbial hydrogen conversion requires elucidation of the interplay of proton and electron transfer events at the H-cluster. We performed real-time spectroscopy on [FeFe]-hydrogenase protein films under controlled variation of atmospheric gas composition, sample pH, and reductant concentration. Attenuated total reflection Fourier-transform infrared spectroscopy was used to monitor shifts of the CO/CN- vibrational bands in response to redox and protonation changes. Three different [FeFe]-hydrogenases and several protein and cofactor variants were compared, including element and isotopic exchange studies. A protonated equivalent (HoxH) of the oxidized state (Hox) was found, which preferentially accumulated at acidic pH and under reducing conditions. We show that the one-electron reduced state Hred′ represents an intrinsically protonated species. Interestingly, the formation of HoxH and Hred′ was independent of the established proton pathway to the diiron site. Quantum chemical calculations of the respective CO/CN- infrared band patterns favored a cysteine ligand of the [4Fe-4S] cluster as the protonation site in HoxH and Hred′. We propose that proton-coupled electron transfer facilitates reduction of the [4Fe-4S] cluster and prevents premature formation of a hydride at the catalytic diiron site. Our findings imply that protonation events both at the [4Fe-4S] cluster and at the diiron site of the H-cluster are important in the hydrogen conversion reaction of [FeFe]-hydrogenases. © 2018 the Owner Societies.

What happens when extra vibrational energy is added to water? Using nonequilibrium molecular dynamics simulations, also including the full electronic structure, and novel descriptors, based on projected vibrational density of states, we are able to follow the flow of excess vibrational energy from the excited stretching and bending modes. We find that the energy relaxation, mostly mediated by a stretching-stretching coupling in the first solvation shell, is highly heterogeneous and strongly depends on the local environment, where a strong hydrogen bond network can transport energy with a time scale of 200 fs, whereas a weaker network can slow down the transport by a factor 2-3. Copyright © 2018 American Chemical Society.

This study investigated the influence of segregations on hydrogen environment embrittlement (HEE) of AISI 304L type austenitic stainless steels. The microstructure of tensile specimens, that were fabricated from commercially available AISI 304L steels and tested by means of small strain-rate tensile tests in air as well as hydrogen gas at room temperature, was investigated by means of combined EDS and EBSD measurements. It was shown that two different austenitic stainless steels having the same nominal alloy composition can exhibit different susceptibilities to HEE due to segregation effects resulting from different production routes (continuous casting/electroslag remelting). Local segregation-related variations of the austenite stability were evaluated by thermodynamic and empirical calculations. The alloying element Ni exhibits pronounced segregation bands parallel to the rolling direction of the material, which strongly influences the local austenite stability. The latter was revealed by generating and evaluating two-dimensional distribution maps for the austenite stability. The formation of deformation-induced martensite was shown to be restricted to segregation bands with a low Ni content. Furthermore, it was shown that the formation of hydrogen induced surface cracks is strongly coupled with the existence of surface regions of low Ni content and accordingly low austenite stability. In addition, the growth behavior of hydrogen-induced cracks was linked to the segregation-related local austenite stability. © 2018 The Author(s).

In order to design more powerful electrocatalysts, developing our understanding of the role of the surface structure and composition of widely abundant bulk materials is crucial. This is particularly true in the search for alternative hydrogen evolution reaction (HER) catalysts to replace platinum. We report scanning electrochemical cell microscopy (SECCM) measurements of the (111)-crystal planes of Fe4.5Ni4.5S8, a highly active HER catalyst. In combination with structural characterization methods, we show that this technique can reveal differences in activity arising from even the slightest compositional changes. By probing electrochemical properties at the nanoscale, in conjunction with complementary structural information, novel design principles are revealed for application to rational material synthesis. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Solar-powered electrochemical production of hydrogen through water electrolysis is an active and important research endeavor. However, technologies and roadmaps for implementation of this process do not exist. In this perspective paper, we describe potential pathways for solar-hydrogen technologies into the marketplace in the form of photoelectrochemical or photovoltaic-driven electrolysis devices and systems. We detail technical approaches for device and system architectures, economic drivers, societal perceptions, political impacts, technological challenges, and research opportunities. Implementation scenarios are broken down into short-term and long-term markets, and a specific technology roadmap is defined. In the short term, the only plausible economical option will be photovoltaic-driven electrolysis systems for niche applications. In the long term, electrochemical solar-hydrogen technologies could be deployed more broadly in energy markets but will require advances in the technology, significant cost reductions, and/or policy changes. Ultimately, a transition to a society that significantly relies on solar-hydrogen technologies will benefit from continued creativity and influence from the scientific community. © 2018 The Royal Society of Chemistry.

Inspired by our recent finding that Fe4.5Ni4.5S8 rock is a highly active electrocatalyst for HER, we set out to explore the influence of the Fe:Ni ratio on the performance of the catalyst. We herein describe the synthesis of (FexNi1-x)9S8 (x = 0-1) along with a detailed elemental composition analysis. Furthermore, using linear sweep voltammetry, we show that the increase in the iron or nickel content, respectively, lowers the activity of the electrocatalyst toward HER. Electrochemical surface area analysis (ECSA) clearly indicates the highest amount of active sites for a Fe:Ni ratio of 1:1 on the electrode surface pointing at an altered surface composition of iron and nickel for the other materials. Specific metal-metal interactions seem to be of key importance for the high electrocatalytic HER activity, which is supported by DFT calculations of several surface structures using the surface energy as a descriptor of catalytic activity. In addition, we show that a temperature increase leads to a significant decrease of the overpotential and gain in HER activity. Thus, we showcase the necessity to investigate the material structure, composition and reaction conditions when evaluating electrocatalysts. © 2017 American Chemical Society.

[FeFe]-hydrogenases efficiently catalyzes hydrogen conversion at a unique [4Fe–4S]-[FeFe] cofactor, the so-called H-cluster. The catalytic reaction occurs at the diiron site, while the [4Fe–4S] cluster functions as a redox shuttle. In the oxidized resting state (Hox), the iron ions of the diiron site bind one cyanide (CN−) and carbon monoxide (CO) ligand each and a third carbonyl can be found in the Fe–Fe bridging position (µCO). In the presence of exogenous CO, A fourth CO ligand binds at the diiron site to form the oxidized, CO-inhibited H-cluster (Hox-CO). We investigated the reduced, CO-inhibited H-cluster (Hred´-CO) in this work. The stretching vibrations of the diatomic ligands were monitored by attenuated total reflection Fourier-transform infrared spectroscopy (ATR FTIR). Density functional theory (DFT) at the TPSSh/TZVP level was employed to analyze the cofactor geometry, as well as the redox and protonation state of the H-cluster. Selective 13CO isotope editing, spectro-electrochemistry, and correlation analysis of IR data identified a one-electron reduced, protonated [4Fe–4S] cluster and an apical CN− ligand at the diiron site in Hred´-CO. The reduced, CO-inhibited H-cluster forms independently of the sequence of CO binding and cofactor reduction, which implies that the ligand rearrangement at the diiron site upon CO inhibition is independent of the redox and protonation state of the [4Fe–4S] cluster. The relation of coordination dynamics to cofactor redox and protonation changes in hydrogen conversion catalysis and inhibition is discussed. © 2018 by the authors.

SrTiO3 is a well-known photocatalyst inducing overall water splitting when exposed to UV irradiation of wavelengths <370 nm. However, the apparent quantum efficiency of SrTiO3 is typically low, even when functionalized with nanoparticles of Pt or Ni@NiO. Here, we introduce a simple solid-state preparation method to control the incorporation of magnesium into the perovskite structure of SrTiO3. After deposition of Pt or Ni@NiO, the photocatalytic water-splitting efficiency of the Mg:SrTiOx composites is up to 20 times higher compared to SrTiO3 containing similar catalytic nanoparticles, and an apparent quantum yield (AQY) of 10 % can be obtained in the wavelength range of 300–400 nm. Detailed characterization of the Mg:SrTiOx composites revealed that Mg is likely substituting the tetravalent Ti ion, leading to a favorable surface–space–charge layer. This originates from tuning of the donor density in the cubic SrTiO3 structure by Mg incorporation and enables high oxygen-evolution rates. Nevertheless, interfacing with an appropriate hydrogen evolution catalyst is mandatory and non-trivial to obtain high-performance in water splitting. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

[FeFe]-Hydrogenases efficiently catalyze the uptake and evolution of H2 due to the presence of an inorganic [6Fe-6S]-cofactor (H-cluster). This cofactor is comprised of a [4Fe-4S] cluster coupled to a unique [2Fe] cluster where the catalytic turnover of H2/H+ takes place. We herein report on the synthesis of a selenium substituted [2Fe] cluster [Fe2{μ(SeCH2)2NH}(CO)4(CN)2]2- (ADSe) and its successful in vitro integration into the native protein scaffold of [FeFe]-hydrogenases HydA1 from Chlamydomonas reinhardtii and CpI from Clostridium pasteurianum yielding fully active enzymes (HydA1-ADSe and CpI-ADSe). FT-IR spectroscopy and X-ray structure analysis confirmed the presence of structurally intact ADSe at the active site. Electrochemical assays reveal that the selenium containing enzymes are more biased towards hydrogen production than their native counterparts. In contrast to previous chalcogenide exchange studies, the S to Se exchange herein is not based on a simple reconstitution approach using ionic cluster constituents but on the in vitro maturation with a pre-synthesized selenium-containing [2Fe] mimic. The combination of biological and chemical methods allowed for the creation of a novel [FeFe]-hydrogenase with a [2Fe2Se]-active site which confers individual catalytic features. © 2017 The Royal Society of Chemistry.

Synthetic pentlandite (Fe4.5Ni4.5S8) is a promising electrocatalyst for hydrogen evolution, demonstrating high current densities, low overpotential, and remarkable stability in bulk form. The depletion of sulfur from the surface of this catalyst during the electrochemical reaction has been proposed to be beneficial for its catalytic performance, but the role of sulfur vacancies and the mechanism determining the reaction kinetics are still unknown. We have performed electrochemical operando studies of the vibrational dynamics of pentlandite under hydrogen evolution reaction conditions using 57Fe nuclear resonant inelastic X-ray scattering. Comparing the measured Fe partial vibrational density of states with density functional theory calculations, we have demonstrated that hydrogen atoms preferentially occupy substitutional positions replacing pre-existing sulfur vacancies. Once all vacancies are filled, the protonation proceeds interstitially, which slows down the reaction. Our results highlight the beneficial role of sulfur vacancies in the electrocatalytic performance of pentlandite and give insights into the hydrogen adsorption mechanism during the reaction. © 2017 American Chemical Society.

Atomistic simulations of thermal desorption spectra for effusion from bulk materials to characterize binding or trapping sites are a challenging task as large system sizes as well as extended time scales are required. Here, we introduce an approach where we combine kinetic Monte Carlo with an analytic approximation of the superbasins within the framework of absorbing Markov chains. We apply our approach to the effusion of hydrogen from BCC iron, where the diffusion within bulk grains is coarse grained using absorbingMarkov chains, which provide an exact solution of the dynamics within a superbasin. Our analytic approximation to the superbasin is transferable with respect to grain size and elliptical shapes and can be applied in simulations with constant temperature as well as constant heating rate. The resulting thermal desorption spectra are in close agreement with direct kinetic Monte Carlo simulations, but the calculations are computationally much more efficient. Our approach is thus applicable to much larger system sizes and provides a first step towards an atomistic understanding of the influence of structural features on the position and shape of peaks in thermal desorption spectra. © 2017 The Author(s) Published by the Royal Society. All rights reserved.

The catalytic hydrogenation of ethyl acetate to ethanol was studied at ambient pressure in the temperature range from 463 K to 513 K using Cu/ZrO2 catalysts obtained by co-precipitation as a function of the Cu loading. The hydrogenation was established as a reproducible probe reaction by determining optimal reaction parameters without deactivation or thermodynamic limitations. Power-law kinetics were determined yielding an apparent activation energy of 74 kJ mol−1 and reaction orders of 0.1–0.3 for H2 and −0.4 to 0.1 for ethyl acetate in the temperature range from 473 K to 503 K. Metallic Cu was found to be essential for the hydrogenation, but the catalytic activity was not proportional to the Cu surface area derived from N2O decomposition and temperature-programmed H2 desorption experiments identifying Cu/ZrO2 as bifunctional catalyst. The acidic sites of the ZrO2 matrix were probed by temperature-programmed experiments with ethyl acetate and NH3. Cu0 is assumed to provide atomic hydrogen by dissociative adsorption and spillover, but the reaction rate is more affected by the tight contact between the embedded Cu nanoparticles and the X-ray amorphous ZrO2 matrix. © 2017 Elsevier Inc.

H2 turnover at the [FeFe]-hydrogenase cofactor (H-cluster) is assumed to follow a reversible heterolytic mechanism, first yielding a proton and a hydrido-species which again is double-oxidized to release another proton. Three of the four presumed catalytic intermediates (Hox, Hred/Hred and Hsred) were characterized, using various spectroscopic techniques. However, in catalytically active enzyme, the state containing the hydrido-species, which is eponymous for the proposed heterolytic mechanism, has yet only been speculated about. We use different strategies to trap and spectroscopically characterize this transient hydride state (Hhyd) for three wild-type [FeFe]-hydrogenases. Applying a novel set-up for real-time attenuated total-reflection Fourier-transform infrared spectroscopy, we monitor compositional changes in the state-specific infrared signatures of [FeFe]-hydrogenases, varying buffer pH and gas composition. We selectively enrich the equilibrium concentration of H hyd, applying Le Chatelier's principle by simultaneously increasing substrate and product concentrations (H2/H+). Site-directed manipulation, targeting either the proton-transfer pathway or the adt ligand, significantly enhances Hhyd accumulation independent of pH. © The Author(s) 2017.

A combined hydrogen peroxide evaporation and hydrogen low-pressure plasma treatment process for sterilization is introduced and investigated. The combination of hydrogen peroxide evaporation followed by hydrogen plasma treatment offers an advantage regarding sterilization in complex metal geometries or in sealed sterile bags, where plasma treatment alone faces challenges. Within this contribution, the droplet size and film homogeneity after condensation is investigated by optical diagnostics. Sterilization tests with common challenge organisms show the sterilization capabilities of the combined process in a process challenge device, mimicking the worst-case-scenario for plasma treatment in a small metal box. Furthermore, sterilization in sealed sterile bags clearly demonstrates the advantage of the combined process, showing full spore inactivation solely for the combined process. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

During application, electrocatalysts are exposed to harsh electrochemical conditions, which can induce degradation. This work addresses the degradation of AuPd bimetallic catalysts used for the electrocatalytic production of hydrogen peroxide (H2O2) by the oxygen reduction reaction (ORR). Potential-dependent changes in the AuPd surface composition occur because the two metals have different dissolution onset potentials, resulting in catalyst dealloying. Using a scanning flow cell (SFC) with an inductively coupled plasma mass spectrometer (ICP-MS), simultaneous Pd and/or Au dissolution can be observed. Thereafter, three accelerated degradation protocols (ADPs), simulating different dissolution regimes, are employed to study the catalyst structure degradation on the nanoscale with identical location (IL) TEM. When only Pd or both Au and Pd dissolve, the composition changes rapidly and the surface becomes enriched with Au, as observed by cyclic voltammetry and elemental mapping. Such changes are mirrored by the evolution of electrocatalytic performances toward H2O2 production. Our experimental findings are finally summarized in a dissolution/structure/selectivity mechanism, providing a clear picture of the degradation of bimetallic catalyst used for H2O2 synthesis. © 2017 American Chemical Society.

This paper gives an overview of recent progress in microstructure-specific hydrogen mapping techniques. The challenging nature of mapping hydrogen with high spatial resolution, i.e. at the scale of finest microstructural features, led to the development of various methodologies: thermal desorption spectrometry, silver decoration, the hydrogen microprint technique, secondary ion mass spectroscopy, atom probe tomography, neutron radiography, and the scanning Kelvin probe. These techniques have different characteristics regarding spatial and temporal resolution associated with microstructure-sensitive hydrogen detection. Employing these techniques in a site-specific manner together with other microstructure probing methods enables multi-scale, quantitative, three-dimensional, high spatial, and kinetic resolution hydrogen mapping, depending on the specific multi-probe approaches used. Here, we present a brief overview of the specific characteristics of each method and the progress resulting from their combined application to the field of hydrogen embrittlement. © 2017 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.

Synthetic diiron compounds of the general formula Fe2(μ-S2R)(CO)n(L)6-n (R = alkyl or aromatic groups; L = CN- or phosphines) are versatile models for the active-site cofactor of hydrogen turnover in [FeFe]-hydrogenases. A series of 18 diiron compounds, containing mostly a dithiolate bridge and terminal ligands of increasing complexity, was characterized by X-ray absorption and emission spectroscopy in combination with density functional theory. Fe K-edge absorption and Kβ main-line emission spectra revealed the varying geometry and the low-spin state of the Fe(i) centers. Good agreement between experimental and calculated core-to-valence-excitation absorption and radiative valence-to-core-decay emission spectra revealed correlations between spectroscopic and structural features and provided access to the electronic configuration. Four main effects on the diiron core were identified, which were preferentially related to variation either of the dithiolate or of the terminal ligands. Alteration of the dithiolate bridge affected mainly the Fe-Fe bond strength, while more potent donor substitution and ligand field asymmetrization changed the metal charge and valence level localization. In contrast, cyanide ligation altered all relevant properties and, in particular, the frontier molecular orbital energies of the diiron core. Mutual benchmarking of experimental and theoretical parameters provides guidelines to verify the electronic properties of related diiron compounds. © 2017 The Royal Society of Chemistry.

We describe the fabrication of a self-powered ethanol biosensor comprising a β-NAD+-dependent alcohol dehydrogenase (ADH) bioanode and a bienzymatic alcohol oxidase (AOx) and horseradish peroxidase (HRP) biocathode. β-NAD+ is regenerated by means of a specifically designed phenothiazine dye (i.e. toluidine blue, TB) modified redox polymer in which TB was covalently anchored to a hexanoic acid tethered poly(4-vinylpyridine) backbone. The redox polymer acts as an immobilization matrix for ADH. Using a carefully chosen anchoring strategy through the formation of amide bonds, the potential of the TB-based mediator is shifted to more positive potentials, thus preventing undesired O2 reduction. To counterbalance the rather high potential of the TB-modified polymer, and thus the bioanode, a high-potential AOx/HRP-based biocathode is suggested. HRP is immobilized in a direct-electron-transfer regime on screen-printed graphite electrodes functionalized with multi-walled carbon nanotubes. The nanostructured cathode ensures the wiring of the iron-oxo complex within oxidized HRP, and thus a high potential for the reduction of H2O2 of about +550mV versus Ag/AgCl/3M KCl. The proposed biofuel cell exhibits an open-circuit voltage (OCV) of approximately 660mV and was used as self-powered device for the determination of the ethanol content in liquor. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The catalytic cofactor of [FeFe]-hydrogenses (H-cluster) is composed of a generic cubane [4Fe-4S]-cluster (4FeH) linked to a binuclear iron-sulfur cluster (2FeH) that has an open coordination site at which the reversible conversion of protons to molecular hydrogen occurs. The (2FeH) subsite features a diatomic coordination sphere composed of three CO and two CN- ligands affecting its redox properties and providing excellent probes for FTIR spectroscopy. The CO stretch vibrations are very sensitive to the redox changes within the H-cluster occurring during the catalytic cycle, whereas the CN- signals seem to be relatively inert to these effects. This could be due to the more structural role of the CN- ligands tightly anchoring the (2FeH) unit to the protein environment through hydrogen bonding. In this work we explore the effects of structural changes within the secondary ligand sphere affecting the CN- ligands on FTIR spectroscopy and catalysis. By comparing the FTIR spectra of wild-type enzyme and two mutagenesis variants, we are able to assign the IR signals of the individual CN- ligands of the (2FeH) site for different redox states of the H-cluster. Moreover, protein film electrochemistry reveals that targeted manipulation of the secondary coordination sphere of the proximal CN- ligand (i.e., closest to the (4FeH) site) can affect the catalytic bias. These findings highlight the importance of the protein environment for re-adjusting the catalytic features of the H-cluster in individual enzymes and provide valuable information for the design of artificial hydrogenase mimics. © 2017 American Chemical Society.

The adsorption of hydrogen at nonpolar GaN(1100) surfaces and its impact on the electronic and vibrational properties is investigated using surface electron spectroscopy in combination with density functional theory (DFT) calculations. For the surface mediated dissociation of H2 and the subsequent adsorption of H, an energy barrier of 0.55 eV has to be overcome. The calculated kinetic surface phase diagram indicates that the reaction is kinetically hindered at low pressures and low temperatures. At higher temperatures ab initio thermodynamics show, that the H-free surface is energetically favored. To validate these theoretical predictions experiments at room temperature and under ultrahigh vacuum conditions were performed. They reveal that molecular hydrogen does not dissociatively adsorb at the GaN(1100) surface. Only activated atomic hydrogen atoms attach to the surface. At temperatures above 820 K, the attached hydrogen gets desorbed. The adsorbed hydrogen atoms saturate the dangling bonds of the gallium and nitrogen surface atoms and result in an inversion of the Ga-N surface dimer buckling. The signatures of the Ga-H and N-H vibrational modes on the H-covered surface have experimentally been identified and are in good agreement with the DFT calculations of the surface phonon modes. Both theory and experiment show that H adsorption results in a removal of occupied and unoccupied intragap electron states of the clean GaN(1100) surface and a reduction of the surface upward band bending by 0.4 eV. The latter mechanism largely reduces surface electron depletion. © 2017 authors. Published by the American Physical Society.

Bipolar electrochemistry has been shown to enable and control various kinds of propulsion of nonwired conducting objects: translation, rotation, and levitation. There is a very rapid development in the field of controlled motion combined with other functionalities. Here we integrate two different concepts in one system to generate wireless electrochemical motion of a specifically designed rotor and track its polarization simultaneously by electrochemical light emission. Locally produced hydrogen bubbles at the cathodic pole of the bipolar rotor are the driving force of the motion, whereas [Ru(bpy)3]Cl2 and tripropylamine react at the anodic extremity, thus generating an electrochemiluminescence signal with an intensity directly correlated with the orientation of the rotor arms. This allows in a straightforward way the qualitative visualization of the changing interfacial potential differences during rotation and shows for the first time that light emission can be coupled to autonomously rotating bipolar electrodes. © 2017 American Chemical Society.

Understanding the deactivation of transition-metal carbide catalysts during hydrodeoxygenation (HDO) reactions is of great importance for improving the production of the second generation fuels from biomass. Based on a combined experimental and theoretical study, we present a mechanistic model for the deactivation of molybdenum carbide catalysts during phenol HDO in the presence of water. At increased water pressure, water molecules preferentially bind to the surface, and active sites are no longer accessible for phenol. In line with first principle calculations, experiments reveal that this process is fully reversible because the reduction of the water partial pressure results in a threefold increase in conversion. The direct deoxygenation of phenol was calculated to be the most favorable pathway, which is governed by the structure of the phenol adsorption complex on the surface at high hydrogen coverage. This is consistent with the experimentally observed high benzene selectivity (85 %) for phenol HDO over MoCx/HCS (hollow carbon spheres) catalyst. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

We report a sustainable in vitro system for enzyme-based photohydrogen production. The [FeFe]-hydrogenase HydA1 from Chlamydomonas reinhardtii was tested for photohydrogen production as a proton-reducing catalyst in combination with eight different photosensitizers. Using the organic dye 5-carboxyeosin as a photosensitizer and plant-type ferredoxin PetF as an electron mediator, HydA1 achieves the highest light-driven turnover number (TONHydA1) yet reported for an enzyme-based in vitro system (2.9×106 mol(H2) mol(cat)−1) and a maximum turnover frequency (TOFHydA1) of 550 mol(H2) mol(HydA1)−1 s−1. The system is fueled very effectively by ambient daylight and can be further simplified by using 5-carboxyeosin and HydA1 as a two-component photosensitizer/biocatalyst system without an additional redox mediator. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

We investigated hydrogen embrittlement in Ni-based superalloy 718 by tensile testing at slow strain rate (10−4 s−1) under continuous electrochemical hydrogen charging. Hydrogen-assisted cracking mechanisms were studied via electron backscatter diffraction (EBSD) analysis and electron channeling contrast imaging (ECCI). In order to elucidate the effects of stress or strain in the cracking mechanisms, material conditions with different strength levels were investigated, including samples in solution annealed (as water quenched) and 780 °C age-hardened states. The microstructure observations in the vicinity of the cracks enabled us to establish correlations between the microstructure, crack initiation sites, and crack propagation pathways. Fracture in the hydrogen-charged samples was dominated by localized plastic deformation. Strain-controlled transgranular cracking was caused by shear localization due to hydrogen-enhanced localized plasticity (HELP) and void nucleation and coalescence along {111} slip planes in both, the solution annealed and age-hardened materials. Stress-assisted intergranular cracking in the presence of hydrogen was only observed in the high strength age-hardened material, due to slip localization at grain boundaries, grain boundary triple junction cracking, and δ/γ-matrix interface cracking. To investigate the effect of δ-phase in crack propagation along grain boundaries, the over-aged state (aged at 870 °C) with different precipitation conditions for the δ-phase was also investigated. Observations confirmed that presence of δ-phase promotes hydrogen-induced intergranular failure by initializing micro-cracks from δ/γ interfaces. © 2017 Acta Materialia Inc.

Nitrogen-doped carbon nanotubes (NCNTs) were used as a support for iron (Fe) nanoparticles applied in carbon dioxide (CO2) hydrogenation at 633 K and 25 bar (1 bar = 105 Pa). The Fe/NCNT catalyst promoted with both potassium (K) and manganese (Mn) showed high performance in CO2 hydrogenation, reaching 34.9% conversion with a gas hourly space velocity (GHSV) of 3.1 L·(g·h)−1. Product selectivities were high for olefin products and low for short-chain alkanes for the K-promoted catalysts. When Fe/NCNT catalyst was promoted with both K and Mn, the catalytic activity was stable for 60 h of reaction time. The structural effect of the Mn promoter was demonstrated by X-ray diffraction (XRD), temperature-programmed reduction (TPR) with molecular hydrogen (H2), and in situ X-ray absorption near-edge structure (XANES) analysis. The Mn promoter stabilized wüstite (FeO) as an intermediate and lowered the TPR onset temperature. Catalytic ammonia (NH3) decomposition was used as an additional probe reaction for characterizing the promoter effects. The Fe/NCNT catalyst promoted with both K and Mn had the highest catalytic activity, and the Mn-promoted Fe/NCNT catalysts had the highest thermal stability under reducing conditions. © 2017 THE AUTHORS

The overriding obstacle to mass production of hydrogen from water as the premium fuel for powering our planet is the frustratingly slow kinetics of the oxygen evolution reaction (OER). Additionally, inadequate understanding of the key barriers of the OER is a hindrance to insightful design of advanced OER catalysts. This study presents ultrathin amorphous high-surface area nickel boride (NixB) nanosheets as a low-cost, very efficient and stable catalyst for the OER for electrochemical water splitting. The catalyst affords 10 mA cm-2 at 0.38 V overpotential during OER in 1.0 m KOH, reducing to only 0.28 V at 20 mA cm-2 when supported on nickel foam, which ranks it among the best reported nonprecious catalysts for oxygen evolution. Operando X-ray absorption fine-structure spectroscopy measurements reveal prevalence of NiOOH, as well as Ni-B under OER conditions, owing to a Ni-B core at nickel oxyhydroxide shell (Ni-B at NiOxH) structure, and increase in disorder of the NiOxH layer, thus revealing important insight into the transient states of the catalyst during oxygen evolution. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The hydrogen distribution in an austenite-martensite dual-phase steel was investigated using silver decoration and scanning Kelvin probe force microscopy. The silver decoration technique optimized for spacial resolution reveals interfacial segregation of hydrogen along the plate-type martensite-martensite grain boundaries. In addition, the scanning Kelvin probe force microscopy kinetically elucidates that hydrogen preferentially diffused out from the martensite-martensite grain boundaries. These preferential sites of hydrogen desorption correspond to the regions of hydrogen-assisted damage. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Metals are key materials for modern manufacturing and infrastructures as well as transpot and energy solutions owing to their strength and formability. These properties can severely deteriorate when they contain hydrogen, leading to unpredictable failure, an effect called hydrogen embrittlement. Here we report that hydrogen in an equiatomic CoCrFeMnNi high-entropy alloy (HEA) leads not to catastrophic weakening, but instead increases both, its strength and ductility. While HEAs originally aimed at entropy-driven phase stabilization, hydrogen blending acts opposite as it reduces phase stability. This effect, quantified by the alloy's stacking fault energy, enables nanotwinning which increases the material's work-hardening. These results turn a bane into a boon: hydrogen does not generally act as a harmful impurity, but can be utilized for tuning beneficial hardening mechanisms. This opens new pathways for the design of strong, ductile, and hydrogen tolerant materials. © 2017 The Author(s).

The realization of metal nanoparticles (NPs) with bimetallic character and distinct composition for specific catalytic applications is an intensively studied field. Due to the synergy between metals, most bimetallic particles exhibit unique properties that are hardly provided by the individual monometallic counterparts. However, as small-sized NPs possess high surface energy, agglomeration during catalytic reactions is favored. Sufficient stabilization can be achieved by confinement of NPs in porous support materials. In this sense, metal-organic frameworks (MOFs) in particular have gained a lot of attention during the last years; however, encapsulation of bimetallic species remains challenging. Herein, the exclusive embedding of preformed core-shell PdPt and RuPt NPs into chemically robust Zr-based MOFs is presented. Microstructural characterization manifests partial retention of the core-shell systems after successful encapsulation without harming the crystallinity of the microporous support. The resulting chemically robust NP@UiO-66 materials exhibit enhanced catalytic activity towards the liquid-phase hydrogenation of nitrobenzene, competitive with commercially used Pt on activated carbon, but with superior size-selectivity for sterically varied substrates. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hydrogen and fuels derived from it will serve as the energy carriers of the future. The associated rapidly growing demand for hydrogen energy-related infrastructure materials has stimulated multiple engineering and scientific studies on the hydrogen embrittlement resistance of various groups of high performance alloys. Among these, high-Mn steels have received special attention owing to their excellent strength - ductility - cost relationship. However, hydrogen-induced delayed fracture has been reported to occur in deep-drawn cup specimens of some of these alloys. Driven by this challenge we present here an overview of the hydrogen embrittlement research carried out on high-Mn steels. The hydrogen embrittlement susceptibility of high-Mn steels is particularly sensitive to their chemical composition since the various alloying elements simultaneously affect the material's stacking fault energy, phase stability, hydrogen uptake behavior, surface oxide scales and interstitial diffusivity, all of which affect the hydrogen embrittlement susceptibility. Here, we discuss the contribution of each of these factors to the hydrogen embrittlement susceptibility of these steels and discuss pathways how certain embrittlement mechanisms can be hampered or even inhibited. Examples of positive effects of hydrogen on the tensile ductility are also introduced. © 2017 Hydrogen Energy Publications LLC.

We revealed the effects of hydrogen on the microstructural evolution and passive film properties of a 2205 duplex stainless steel by the joint use of electron backscatter diffraction (EBSD), electron channeling contrast imaging (ECCI), X-ray photoelectron spectroscopy (XPS) and electrochemical measurements. The microstructural analysis results show that effects of hydrogen on the two phases are different: (i) in austenite, stacking faults are induced by hydrogen, and (ii) in ferrite, hydrogen causes an increase of the dislocation density. The XPS analysis revealed that hydrogen reduced the occurrence of Cr2O3 and nitrogen in the passive film, leading to the reduction of their overall thickness. Furthermore, for the first time we demonstrated that the hydrogen release time plays an important role in the electrochemical behavior of the hydrogen charged steel. © 2017 Elsevier B.V.

By doping the TiO2 support with nitrogen, strong metal-support interactions (SMSI) in Pd/TiO2 catalysts can be tailored to obtain high-performance supported Pd nanoparticles (NPs) in nitrobenzene (NB) hydrogenation catalysis. According to the comparative studies by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and diffuse reflectance CO FTIR (CO-DRIFTS), N-doping induced a structural promoting effect, which is beneficial for the dispersion of Pd species on TiO2. High-angle annular dark-field scanning transmission electron microscopy study of Pd on N-doped TiO2 confirmed a predominant presence of sub-2 nm Pd NPs, which are stable under the applied hydrogenation conditions. XPS and CO-DRIFTS revealed the formation of strongly coupled Pd-N species in Pd/TiO2 with N-doped TiO2 as support. Density functional theory (DFT) calculations over model systems with Pdn (n = 1, 5, or 10) clusters deposited on TiO2(101) surface were performed to verify and supplement the experimental observations. In hydrogenation catalysis using NB as a model molecule, Pd NPs on N-doped TiO2 outperformed those on N-free TiO2 in terms of both catalytic activity and stability, which can be attributed to the presence of highly dispersed Pd NPs providing more active sites, and to the formation of Pd-N species favoring the dissociative adsorption of the reactant NB and the easier desorption of the product aniline. (Figure Presented). © 2016 American Chemical Society.

The behaviour of hydrogen at structural defects such as grain boundaries plays a critical role in the phenomenon of hydrogen embrittlement. However, characterization of the energetics and diffusion of hydrogen in the vicinity of such extended defects using conventional ab initio techniques is challenging due to the relatively large system sizes required when dealing with realistic grain boundary geometries. In order to be able to access the required system sizes, as well as high-Throughput testing of a large number of configurations, while remaining within a quantum-mechanical framework, an environmental tight-binding model for the iron-hydrogen system has been developed. The resulting model is applied to study the behaviour of hydrogen at a class of low-energy {110}-Terminated twist grain boundaries in α-Fe. We find that, for particular Σ values within the coincidence site lattice description, the atomic geometry at the interface plane provides extremely favourable trap sites for H, which also possess high escape barriers for diffusion. By contrast, via simulated tensile testing, weakly trapped hydrogen at the interface plane of the bulk-like Σ3 boundary acts as a 'glue' for the boundary, increasing both the energetic barrier and the elongation to rupture. © 2017 The Author(s) Published by the Royal Society. All rights reserved.

Since the addition of Al to high-Mn steels is known to reduce their sensitivity to hydrogen-induced delayed fracture, we investigate possible trapping effects connected to the presence of Al in the grain interior employing density-functional theory (DFT). The role of Al-based precipitates is also investigated to understand the relevance of short-range ordering effects. So-called E21-Fe3AlC κ-carbides are frequently observed in Fe-Mn-Al-C alloys. Since H tends to occupy the same positions as C in these precipitates, the interaction and competition between both interstitials is also investigated via DFT-based simulations. While the individual H–H/C–H chemical interactions are generally repulsive, the tendency of interstitials to increase the lattice parameter can yield a net increase of the trapping capability. An increased Mn content is shown to enhance H trapping due to attractive short-range interactions. Favorable short-range ordering is expected to occur at the interface between an Fe matrix and the E21-Fe3AlC κ-carbides, which is identified as a particularly attractive trapping site for H. At the same time, accumulation of H at sites of this type is observed to yield decohesion of this interface, thereby promoting fracture formation. The interplay of these effects, evident in the trapping energies at various locations and dependent on the H concentration, can be expressed mathematically, resulting in a term that describes the hydrogen embrittlement. © 2017 by the authors. Licensee MDPI, Basel, Switzerland.

Monocrystalline, yet porous mosaic platelets of cobalt ferrite, CoFe2O4, can be synthesized from a layered double hydroxide (LDH) precursor by thermal decomposition. Using an equimolar mixture of Fe2+, Co2+, and Fe3+ during co-precipitation, a mixture of LDH, (FeIICoII)2/3FeIII 1/3(OH)2(CO3)1/6mH2O, and the target spinel CoFe2O4 can be obtained in the precursor. During calcination, the remaining FeII fraction of the LDH is oxidized to FeIII leading to an overall Co2+:Fe3+ ratio of 1:2 as required for spinel crystallization. This pre-adjustment of the spinel composition in the LDH precursor suggests a topotactic crystallization of cobalt ferrite and yields phase pure spinel in unusual anisotropic platelet morphology. The preferred topotactic relationship in most particles is [111]Spinel∥[001]LDH. Due to the anion decomposition, holes are formed throughout the quasi monocrystalline platelets. This synthesis approach can be used for different ferrites and the unique microstructure leads to unusual chemical properties as shown by the application of the ex-LDH cobalt ferrite as catalyst in the selective oxidation of 2-propanol. Compared to commercial cobalt ferrite, which mainly catalyzes the oxidative dehydrogenation to acetone, the main reaction over the novel ex-LDH cobalt is dehydration to propene. Moreover, the oxygen evolution reaction (OER) activity of the ex-LDH catalyst was markedly higher compared to the commercial material. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

We report on the development of an amperometric polymer multilayer-based biosensor for the determination of lactose in the presence of high concentrations of glucose. The sensor platform consists of a two-layer system with the first layer (sensing layer) comprising cellobiose dehydrogenase (CDH) bound by electrostatic interactions in a favourite orientation for efficient direct electron transfer. The second layer on top of the sensing element consists of a specifically designed hydrophilic polymer which co-entraps glucose oxidase (GOx) and catalase (CAT). This bi-enzymatic system is able to remove glucose (up to a concentration of at least 140 mM) in the outer layer of the modified electrode and thus prevents the interfering analyte from reaching the active CDH layer. Moreover, the concomitantly generated H2O2 is efficiently removed by means of CAT. The linear range for the detection of lactose was from 10 to 100 μM. The sensor is able to detect lactose at low concentrations in lactose-free milk samples. Sample pre-treatment consist of a simple dilution step. Quantification of the lactose content in lactose-free dairy products showed that the amount of lactose is below the threshold given by the manufacturer. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

The dissociation of water is an important step in many chemical processes at solid surfaces. In particular, water often spontaneously dissociates near metal oxide surfaces, resulting in a mixture of H2O, H+, and OH- at the interface. Ubiquitous proton-transfer (PT) reactions cause these species to dynamically interconvert, but the underlying mechanisms are poorly understood. Here, we develop and use a reactive high-dimensional neural-network potential based on density functional theory data to elucidate the structural and dynamical properties of the interfacial species at the liquid-water-metal-oxide interface, using the nonpolar ZnO(101̅0) surface as a prototypical case. Molecular dynamics simulations reveal that water dissociation and recombination proceed via two types of PT reactions: (i) to and from surface oxide and hydroxide anions (“surface-PT”) and (ii) to and from neighboring adsorbed hydroxide ions and water molecules (“adlayer-PT”). We find that the adlayer-PT rate is significantly higher than the surface-PT rate. Water dissociation is, for both types of PT, governed by a predominant presolvation mechanism, i.e., thermal fluctuations that cause the adsorbed water molecules to occasionally accept a hydrogen bond, resulting in a decreased PT barrier and an increased dissociation rate as compared to when no hydrogen bond is present. Consequently, we are able to show that hydrogen bond fluctuations govern PT events at the water-metal-oxide interface in a way similar to that in acidic and basic aqueous bulk solutions. © 2017 American Chemical Society.

In nature, [FeFe]-hydrogenases catalyze the uptake and release of molecular hydrogen (H2) at a unique iron-sulfur cofactor. The absence of an electrochemical overpotential in the H2 release reaction makes [FeFe]-hydrogenases a prime example of efficient biocatalysis. However, the molecular details of hydrogen turnover are not yet fully understood. Herein, we characterize the initial one-electron reduction of [FeFe]-hydrogenases by infrared spectroscopy and electrochemistry and present evidence for proton-coupled electron transport during the formation of the reduced state Hred′. Charge compensation stabilizes the excess electron at the [4Fe-4S] cluster and maintains a conservative configuration of the diiron site. The role of Hred′ in hydrogen turnover and possible implications on the catalytic mechanism are discussed. We propose that regulation of the electronic properties in the periphery of metal cofactors is key to orchestrating multielectron processes. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Engineering of controlled hybrid nanocomposites creates one of the most exciting applications in the fields of energy materials and environmental science. The rational design and in situ synthesis of hierarchical porous nanocomposite sheets of nitrogen-doped graphene oxide (NGO) and nickel sulfide (Ni7S6) derived from a hybrid of a well-known nickel-based metal-organic framework (NiMOF-74) using thiourea as a sulfur source are reported here. The nanoporous NGO/MOF composite is prepared through a solvothermal process in which Ni(II) metal centers of the MOF structure are chelated with nitrogen and oxygen functional groups of NGO. NGO/Ni7S6 exhibits bifunctional activity, capable of catalyzing both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) with excellent stability in alkaline electrolytes, due to its high surface area, high pore volume, and tailored reaction interface enabling the availability of active nickel sites, mass transport, and gas release. Depending on the nitrogen doping level, the properties of graphene oxide can be tuned toward, e.g., enhanced stability of the composite compared to commonly used RuO2 under OER conditions. Hence, this work opens the door for the development of effective OER/HER electrocatalysts based on hierarchical porous graphene oxide composites with metal chalcogenides, which may replace expensive commercial catalysts such as RuO2 and IrO2. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nanophase segregation of a bicomponent thiol self-assembled monolayer is predicted using atomistic molecular dynamics simulations and experimentally confirmed. The simulations suggest the formation of domains rich in acid-terminated chains, on one hand, and of domains rich in amide-functionalized ethylene glycol oligomers, on the other hand. In particular, within the amide-ethylene glycol oligomers region, a key role is played by the formation of interchain hydrogen bonds. The predicted phase segregation is experimentally confirmed by the synthesis of 35 and 15 nm gold nanoparticles functionalized with several binary mixtures of ligands. An extensive study by transmission electron microscopy and electron tomography, using silica selective heterogeneous nucleation on acid-rich domains to provide electron contrast, supports simulations and highlights patchy nanoparticles with a trend toward Janus nano-objects depending on the nature of the ligands and the particle size. These results validate our computational platform as an effective tool to predict nanophase separation in organic mixtures on a surface and drive further exploration of advanced nanoparticle functionalization. © 2017 American Chemical Society.

We report on the fabrication of bioanodes for H2 oxidation based on [NiFeSe] hydrogenase. The enzyme was electrically wired by means of a specifically designed low-potential viologen-modified polymer, which delivers benchmark H2 oxidizing currents even under deactivating conditions owing to efficient protection against O2 combined with a viologen-induced reactivation of the O2 inhibited enzyme. Moreover, the viologen-modified polymer allows for electrochemical co-deposition of polymer and biocatalyst and, by this, for control of the film thickness. Protection and reactivation of the enzyme was demonstrated in thick and thin reaction layers. © 2017 American Chemical Society.

We detail a mediator- and membrane-free enzymatic glucose/oxygen biofuel cell based on transparent and nanostructured conducting supports. Chemically modified indium tin oxide nanoparticle modified electrodes were used to substantially increase the active surface area without significantly compromising transparency. Two different procedures for surface nanostructuring were employed, viz. spray-coating and drop-coating. The spray-coated biodevice showed superior characteristics as compared to the drop-coated enzymatic fuel cell, as a result of the higher nanostructured surface area as confirmed by electrochemical characterisation, as well as scanning electron and atomic force microscopy. Subsequent chemical modification with silanes, followed by the immobilisation of either cellobiose dehydrogenase from Corynascus thermophiles or bilirubin oxidase from Myrothecium verrucaria, were performed to obtain the bioanodes and biocathodes, respectively. The optimised biodevice exhibited an OCV of 0.67 V and power output of up to 1.4 µW/cm2 at an operating voltage of 0.35 V. This is considered a significant step forward in the field of glucose/oxygen membrane- and mediator-free, transparent enzymatic fuel cells. © 2017 Elsevier B.V.

The growth of metal–organic framework (ZIF-67) nanocrystals on nickel foam (NF), followed by carbonization in diluted H2, leads to a nitrogen-doped carbon-nanotube-grafted cobalt/carbon polyhedra film on NF. The obtained material serves as a highly active binder-free electrocatalyst for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), enabling high-performance alkaline (0.1 m KOH) water electrolysis with potentials of 1.62 and 0.24 V, respectively, at OER and HER current densities of 10 mA cm−2. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

The development of a versatile microbiosensor for hydrogen detection is reported. Carbon-based microelectrodes were modified with a [NiFe]-hydrogenase embedded in a viologen-modified redox hydrogel for the fabrication of a sensitive hydrogen biosensor By integrating the microbiosensor in a scanning photoelectrochemical microscope, it was capable of serving simultaneously as local light source to initiate photo(bio)electrochemical reactions while acting as sensitive biosensor for the detection of hydrogen. A hydrogen evolution biocatalyst based on photosystem 1-platinum nanoparticle biocomplexes embedded into a specifically designed redox polymer was used as a model for proving the capability of the developed hydrogen biosensor for the detection of hydrogen upon localized illumination. The versatility and sensitivity of the proposed microbiosensor as probe tip allows simplification of the set-up used for the evaluation of complex electrochemical processes and the rapid investigation of local photoelectrocatalytic activity of biocatalysts towards light-induced hydrogen evolution. © 2017 Elsevier B.V.

[FeFe]-Hydrogenases contain a H2-converting cofactor (H-cluster) in which a canonical [4Fe-4S] cluster is linked to a unique diiron site with three carbon monoxide (CO) and two cyanide (CN-) ligands (e.g., in the oxidized state, Hox). There has been much debate whether reduction and hydrogen binding may result in alternative rotamer structures of the diiron site in a single (Hred) or double (Hsred) reduced H-cluster species. We employed infrared spectro-electrochemistry and site-selective isotope editing to monitor the CO/CN- stretching vibrations in [FeFe]-hydrogenase HYDA1 from Chlamydomonas reinhardtii. Density functional theory calculations yielded vibrational modes of the diatomic ligands for conceivable H-cluster structures. Correlation analysis of experimental and computational IR spectra has facilitated an assignment of Hred and Hsred to structures with a bridging hydride at the diiron site. Pronounced ligand rotation during μH binding seems to exclude Hred and Hsred as catalytic intermediates. Only states with a conservative H-cluster geometry featuring a μCO ligand are likely involved in rapid H2 turnover. © 2017 American Chemical Society.

ITQ-8 is a new hydrous layer silicate (HLS) with a chemical composition of [C4H8(C7H13N)2]8 [Si64O128(OH)16]·48H2O per unit cell. The synthesis of ITQ-8 was first described in 2002 by Díaz-Cabañas et al., the structure of this material, however, remained unsolved at that time. Physico-chemical characterization using solid-state NMR spectroscopy, SEM, TG-DTA, and FTIR spectroscopy confirmed that ITQ-8 is a layer silicate. The XRD powder pattern was indexed in the monoclinic system with lattice parameters of a0 = 35.5168(5) Å, b0 = 13.3989(2) Å, c0 = 16.0351(2) Å, β = 106.74(2)°. The crystal structure was solved by simulated annealing. Rietveld refinement of the structure in space group C2/c converged to residual values of RBragg = 0.023, RF = 0.022 and chi2 = 2.3 confirming the structure model. The structure of ITQ-8 contains silicate layers with a topology that resembles a (11-1) section of the framework of zeolite levyne. So far, this layer topology is unique among layer silicates. The layer can be regarded as made up of 4-, 6-, double-six and 8-rings which are interconnected to form cup-like "half-cages". Unlike other HLSs, which possess impermeable silicate layers, ITQ-8 contains 8-rings pores with a free diameter of 3.5 Å × 3.4 Å and can be regarded as a "small-pore layer silicate". In the crystal structure, the organic cations, 1,4-diquiniclidiniumbutane, used as structure directing agents during synthesis are intercalated between the silicate layers. Clusters (bands) of water molecules which are hydrogen bonded to each other and to the terminal Si-OH/Si-O- groups are located between the organic cations and interconnect the silicate layers. ITQ-8 is a very interesting material as precursor for the synthesis of microporous framework silicates by topotactic condensation or interlayer expansion reactions leading to 3D micro-pore systems which may be useful in applications as e.g. catalysts, catalyst supports and adsorbents of for separation. © The Royal Society of Chemistry 2016.

A series of Co-modified Cu/ZnO/Al2O3 methanol synthesis catalysts with different Na loadings was prepared and applied in higher alcohol synthesis (HAS) at 280 °C, 60 bar and a ratio of H2/CO = 1. The bulk and surface properties of the catalysts were characterized after reduction and after 40 h time on stream (TOS) without exposing the catalysts to air during the transfer and the measurements. Increased presence of metallic Co0 after reduction at 350 °C was confirmed by X-ray photoelectron spectroscopy indicating metallic Cu0 to act as a reduction promoter. Catalysts with low Na loadings (≤0.6 wt%) showed strong initial deactivation presumably due to coking of isolated Co0 surface sites favoring hydrocarbon formation. The selectivity to higher alcohols gradually increased during the first 10 h TOS indicating enhanced Cu-Co surface alloy formation considered as active sites for HAS. In contrast, with high Na loadings (≥0.8 wt%) deactivation did not occur and stable performance with constant CO conversion and product distribution was observed indicating significantly altered structural properties. High Na loadings caused the stabilizing amorphous oxide matrix to collapse resulting in strong sintering of the metallic Cu particles, and an increased carbidization of metallic Co0 forming bulk Co2C was observed by X-ray diffraction. Close contact between metallic Co0 and Co2C, which is known to facilitate molecular CO adsorption, is assumed to generate additional active sites for HAS. © 2016 Elsevier Inc. All rights reserved.

[FeFe]-hydrogenases are nature's fastest catalysts for the evolution or oxidation of hydrogen. Numerous synthetic model complexes for the [2Fe] subcluster (2FeH) of their active site are known, but so far none of these could compete with the enzymes. The complex Fe2[μ-(SCH2)2X](CN)2(CO)4 2- with X = NH was shown to integrate into the apo-form of [FeFe]-hydrogenases to yield a fully active enzyme. Here we report the first crystal structures of the apo-form of the bacterial [FeFe]-hydrogenase CpI from Clostridium pasteurianum at 1.60 Å and the active semisynthetic enzyme, CpIADT, at 1.63 Å. The structures illustrate the significant changes in ligand coordination upon integration and activation of the [2Fe] complex. These changes are induced by a rigid 2FeH cavity as revealed by the structure of apoCpI, which is remarkably similar to CpIADT. Additionally we present the high resolution crystal structures of the semisynthetic bacterial [FeFe]-hydrogenases CpIPDT (X = CH2), CpIODT (X = O) and CpISDT (X = S) with changes in the headgroup of the dithiolate bridge in the 2FeH cofactor. The structures of these inactive enzymes demonstrate that the 2FeH-subcluster and its protein environment remain largely unchanged when compared to the active enzyme CpIADT. As the active site shows an open coordination site in all structures, the absence of catalytic activity is probably not caused by steric obstruction. This demonstrates that the chemical properties of the dithiolate bridge are essential for enzyme activity. © 2016 The Royal Society of Chemistry.

Low-pressure plasmas are a promising alternative to modern sterilization processes. As plasma is a surface process, multilayered stacks of spores are a crucial challenge to overcome. Here, a combined process of condensed hydrogen peroxide and hydrogen plasma is analyzed for its efficacy against various spore concentrations showing a clear increase in efficacy using a combined process compared to the two steps used separately. Besides spores, protein contaminations are a major issue in clinics and the combined process is investigated for protein removal efficiency using the well-established BSA model. Furthermore, RNase A serves as a difficult-to-inactivate protein model to investigate protein inactivation efficiency. Finally, inactivation mechanisms of RNase A with a special focus on sulfur-based modifications are investigated using Raman spectroscopy. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hydrogen peroxide (H2O2) is one of the most important reactive oxygen species, and it is involved in a number of cellular processes ranging from signal transduction to immune defence and oxidative stress. It is of great interest to intracellularly quantify H2O2 to improve the understanding of its role in disease processes. In this study, we present an amperometric nanosensor for the quantification of H2O2 at the single-cell level. Deposition of the electrocatalyst Prussian Blue on carbon nanoelectrodes enables selective H2O2 reduction at mild potentials. Owing to their small size and needle-type shape, these nanoelectrodes can penetrate the membrane of single living cells, causing only minimal perturbation. The nanosensors allow for the monitoring of penetration-induced oxidative outbursts as well as the uptake of H2O2 from the extracellular environment in single murine macrophages. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Cu-containing photocathodes are generally limited by fast photocorrosion under working conditions. Hence stabilization of these materials is a key factor in their potential application for the light-induced hydrogen evolution reaction (HER). In order to identify new materials, oxidized Cu-Si-Ti metallic thin film precursor materials libraries were evaluated using a combinatorial approach. High-throughput photoelectrochemical characterization using an automated optical scanning droplet cell was performed on a material library to analyze doping and alloying effects on the light-induced HER. The results revealed that compositions near Ti-doped CuSiO3 (dioptase and copper-polysilicate) and Si-doped Cu3TiOx act as comparatively stable and highly active materials for HER. © 2016 The Royal Society of Chemistry.

An iron based catalyst supported on an N-functionalized carbon nanotube (NCNT) was promoted with potassium and manganese as follows: Fe/NCNT, K/Fe/NCNT, Mn/Fe/NCNT, and K/Mn/Fe/NCNT for CO2 hydrogenation. Time-resolved reduction X-ray absorption near edge spectroscopy (XANES) showed mixed phases of Fe, FeO, Fe3O4, and Fe2O3 resulting from K/Fe/NCNT, and of FeO and Fe3O4 resulting from Mn/Fe/NCNT. The product distributions and growth probability of n-alkanes during CO2 hydrogenation indicated that the potassium-promoted iron catalysts performed Fischer-Tropsch (FT) synthesis under steady state at 60 h. 1-Alkenes desorbed from the FT sites with the potassium-promoted catalysts, (K/Fe/NCNT and K/Mn/Fe/NCNT), with low methane formation. Small amounts of 1-alkene, along with high methanation, were produced from the potassium-unpromoted catalysts, (Fe/NCNT and Mn/Fe/NCNT), indicating high local H2:CO ratios on the catalyst surfaces. K/Fe/NCNT and K/Mn/Fe/NCNT catalysts also produced ethanol. Thus, potassium is a key promoter providing active species of the catalysts for alkene and ethanol formation. Reduced surrounding of the NCNT support, potassium as an electronic promoter together with manganese as a structural promoter made the iron-active phase well suitable for CO2 hydrogenation producing mainly alkenes and ethanol. © 2016 Elsevier B.V.

The dissolution behavior of a single H2 bubble electrochemically generated at a Pt microelectrode in 1 M H2SO4 was studied. The open circuit potential (OCP) relaxation after the polarization end was recorded and correlated with the dissolved H2 concentration at the interface electrode/electrolyte/gas. Simultaneously, the shrinking of the bubble was followed optically by means of a high speed camera. In addition, analytical modeling and numerical simulations for the bubble dissolution were performed. Three characteristic regions are identified in the OCP and the bubble radius transients: (i) slow relaxation and shrinking, (ii) transition region, and (iii) a long-term slowed down dissolution process. The high supersaturation after polarization remains longer than theoretically predicted and feeds the bubble in region (i). This reduces the dissolution rate of the bubble which differs significantly from that of nonelectrochemically produced bubbles. Numerical multispecies simulations prove that oxygen and nitrogen dissolved in the electrolyte additionally influence the bubble dissolution and slow down its shrinkage compared to pure hydrogen diffusion. In region (iii), a complete exchange of hydrogen gas with nitrogen and oxygen has occurred in the gas bubble. © 2016 American Chemical Society.

Electrochemical efficiency and stability are among the most important characteristics of electrocatalysts. These parameters are usually evaluated separately for the anodic and cathodic half-cell reactions in a three-electrode system or by measuring the overall cell voltage between the anode and cathode as a function of current or time. Here, we demonstrate how bipolar electrochemistry can be exploited to evaluate the efficiency of electrocatalysts for full electrochemical water splitting while simultaneously and independently monitoring the individual performance and stability of the half-cell electrocatalysts. Using a closed bipolar electrochemistry setup, all important parameters such as overvoltage, half-cell potential, and catalyst stability can be derived from a single galvanostatic experiment. In the proposed experiment, none of the half-reactions is limiting on the other, making it possible to precisely monitor the contribution of the individual half-cell reactions on the durability of the cell performance. The proposed approach was successfully employed to investigate the long-term performance of a bifunctional water splitting catalyst, specifically amorphous cobalt boride (Co2B), and the durability of the electrocatalyst at the anode and cathode during water electrolysis. Additionally, by periodically alternating the polarization applied to the bipolar electrode (BE) modified with a bifunctional oxygen electrocatalyst, it was possible to explicitly follow the contributions of the oxygen reduction (ORR) and the oxygen evolution (OER) half-reactions on the overall long-term durability of the bifunctional OER/ORR electrocatalyst. © 2016 American Chemical Society.

A multiscale approach is proposed to predict how the presence of hydrogen influences the onset of homogeneous dislocation nucleation (HDN) and thus of plasticity. The model takes inputs that can be solely obtained from atomistic calculations, such as dislocation core structure, stacking fault energy and hydrogen-hydrogen interaction. The equilibrium hydrogen concentration around the dislocation loop is calculated using a recently developed self-consistent iterative method [1]. The complex nature of the dislocation field, as well as the equilibrium hydrogen concentration around the loops, is taken into account. The onset of HDN as a function of bulk hydrogen concentration and temperature is quantitatively predicted and is consistent with nano-indentation experiments on hydrogen loaded samples. Applying the approach to Ni, we find that even low hydrogen concentrations of about 1 at-% result in largely reduced HDN energy barriers and thus largely reduce the critical shear stress. © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Phenothiazine-modified redox hydrogels were synthesized and used for the wiring of the aldehyde oxidoreductase PaoABC to electrode surfaces. The effects of the pH value and electrode surface modification on the biocatalytic activity of the layers were studied in the presence of vanillin as the substrate. The enzyme electrodes were successfully employed as bioanodes in vanillin/O2 biofuel cells in combination with a high potential bilirubin oxidase biocathode. Open circuit voltages of around 700mV could be obtained in a two compartment biofuel cell setup. Moreover, the use of a rather hydrophobic polymer with a high degree of crosslinking sites ensures the formation of stable polymer/enzyme films which were successfully used as bioanode in membrane-less biofuel cells. © 2015 Elsevier B.V.

At the water-air interface, the hydrogen-bond network of water molecules is interrupted, and accordingly, the structure and dynamics of the interfacial water molecules are altered considerably compared with the bulk. Such interfacial water molecules have been studied by surface-specific vibrational sum-frequency generation (SFG) spectroscopy probing high-frequency O-H stretch and H-O-H bending modes. In contrast, the low-frequency librational mode has been much less studied with SFG. Because this mode is sensitive to the hydrogen-bond connectivity, understanding the librational mode of the interfacial water is crucial for unveiling a microscopic view of the interfacial water. Here, we compute the SFG librational mode spectra at the water-air interface by using molecular dynamics simulation. We show that the modeling of the polarizability has a drastic effect on the simulated librational mode spectra, whereas the spectra are less sensitive to the force field models and the modeling of the dipole moment. The simulated librational spectra display a peak centered at ∼700 cm-1, which is close to the infrared peak frequency of the liquid water librational mode of 670 cm-1. This indicates that the librational mode of the interfacial water at the water-air interface closely resembles that of bulk liquid water. © 2016 American Chemical Society.

Memory effects in Li-ion battery materials have been explained on the basis of the thermodynamics of many-particles body, however the role of the (de-)intercalation kinetics is not yet clear. We demonstrate that kinetic aspects, specifically Li-ion mobility, are determining the magnitude of the memory effect in TiO2 by studying samples with different levels of oxygen vacancies. © The Royal Society of Chemistry 2016.

We propose a new force field for trimethylamine N-oxide (TMAO), which is designed to reproduce the long-lived and highly directional hydrogen bond between the TMAO oxygen (OTMAO) atom and surrounding water molecules. Based on the data obtained by ab initio molecular dynamics simulations, we introduce three dummy sites around OTMAO to mimic the OTMAO lone pairs and we migrate the negative charge on the OTMAO to the dummy sites. The force field model developed here improves both structural and dynamical properties of aqueous TMAO solutions. Moreover, it reproduces the experimentally observed dependence of viscosity upon increasing TMAO concentration quantitatively. The simple procedure of the force field construction makes it easy to implement in molecular dynamics simulation packages and makes it compatible with the existing biomolecular force fields. This paves the path for further investigation of protein-TMAO interaction in aqueous solutions. © 2016 Author(s).

Metallic iridium and ruthenium as well as their oxides are among the most active oxygen evolution (OER) electrocatalysts in acidic media, and are also of interest for the catalysis of the hydrogen evolution (HER). The stability of these materials under different operating conditions is, however, still not fully understood. In the current work, activity and stability of well-defined Ru, RuO2, Ir, and IrO2 thin film electrodes are evaluated in acidic and alkaline electrolytes using an electrochemical scanning flow cell (SFC) connected to an inductively coupled plasma mass spectrometer (ICP-MS). Identical experimental protocols are intentionally employed for all electrodes and electrolytes, to obtain unambiguous and comparable information on intrinsic activity and stability of the electrodes. It is found that independent of the electrolyte, OER activity decreases as Ru > Ir ≈ RuO2 > IrO2, while dissolution increases as IrO2 « RuO2 < Ir « Ru. Moreover, dissolution of these metals in both solutions is 2-3 orders of magnitude higher compared to their respective oxides, and dissolution is generally more intense in alkaline solutions. Similarly to the OER, metallic electrodes are more active catalysts for HER. They, however, suffer from dissolution during native oxide reduction, while IrO2 and RuO2 do not exhibit significant dissolution. The obtained results on activity and stability of the electrodes are discussed in light of their potential applications, i.e. water electrolysers or fuel cells. © 2015 Elsevier B.V.

An advanced approach based on scanning electrochemical microscopy (SECM) was used to investigate the kinetics of the oxygen reduction reaction (ORR) on multiwalled carbon nanotubes (MWCNTs) and a composite of MWCNTs and cobalt (IX) protoporphyrin (MWCNTs/CoP). The amount of hydrogen peroxide produced during ORR was studied as a function of catalyst loading in an electrolyte of pH 7. Additionally, a Pt ultra microelectrode (UME) was used to determine changes in interfacial oxygen concentration from which intrinsic rate constants of heterogeneous electron transfer during the ORR were calculated. The amount of hydrogen peroxide produced and the number of electrons exchanged during oxygen reduction, and the heterogeneous electron transfer rate constants determined using SECM were compared with the corresponding values obtained using methods based on forced convection, namely RRDE and RDE. It was found that SECM offers some advantages compared to RDE or RRDE with regard to accuracy in determining the number of electrons transferred during the ORR, particularly in the case of thick and porous catalyst films. However, the heterogeneous electron transfer rate constants were similar for both methods, indicating that the determination of the surface concentration of reactants using RC-SECM suffers from some drawbacks. © 2015 Elsevier B.V.

We investigated the hydrogen distribution and desorption behavior in an electrochemically hydrogen-charged binary Ni-Nb model alloy to study the role of δ phase in hydrogen embrittlement of alloy 718. We focus on two aspects, namely, (1) mapping the hydrogen distribution with spatial resolution enabling the observation of the relations between desorption profiles and desorption sites; and (2) correlating these observations with mechanical testing results to reveal the degradation mechanisms. The trapping states of hydrogen in the alloy were globally analyzed by Thermal Desorption Spectroscopy (TDS). Additionally, spatially resolved hydrogen mapping was conducted using silver decoration, Scanning Kelvin Probe Force Microscopy (SKPFM) and Secondary Ion Mass Spectrometry (SIMS): The Ag decoration method revealed rapid effusion of hydrogen at room temperature from the γ-matrix. The corresponding kinetics was resolved in both, space and time by the SKPFM measurements. At room temperature the hydrogen release from the γ-matrix steadily decreased until about 100 h and then was taken over by the δ phase from which the hydrogen was released much slower. For avoiding misinterpretation of hydrogen signals stemming from environmental effects we also charged specimens with deuterium. The deuterium distribution in the microstructure was studied by SIMS. The combined results reveal that hydrogen dissolves more preferably inside the γ-matrix and is diffusible at room temperature while the δ phase acts as a deeper trapping site for hydrogen. With this joint and spatially resolving approach we observed the microstructure- and time-dependent distribution and release rate of hydrogen with high spatial and temporal resolution. Correlating the obtained results with mechanical testing of the hydrogen-charged samples shows that hydrogen enhanced decohesion (HEDE) occurring at the δ/matrix interfaces promotes the embrittlement. © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The desorption kinetics of hydrogen from a polycrystalline Cu/ZrO2 catalyst was investigated under atmospheric pressure using temperature-programmed desorption (TPD) experiments in a microreactor set-up. Different heating rates were applied under equal conditions with a carefully reduced catalyst. The hydrogen TPD peaks were symmetric and centered slightly above 300 K indicating associative desorption of H2 from metallic Cu. Using heating rate variation, the kinetic parameters Ades and Edes were determined to be 1.24 × 109 s-1 and 68 kJ mol-1, respectively. As the modeling with constant values of Ades and Edes yielded signals which were too narrow, dependence of Edes on coverage was introduced applying Edes - K (ΘH)n. By application of the "full-analysis" method an optimal fit to the experimental data was found. Setting n = 1 resulted in the best fit and a value of 61 kJ mol-1 - (6.25 kJ mol-1 × ΘH) for Edes was determined. © Springer Science+Business Media New York 2016.

For understanding the underlying hydrogen embrittlement mechanism in transformation-induced plasticity steels, the process of damage evolution in a model austenite/martensite dual-phase microstructure following hydrogenation was investigated through multi-scale electron channelling contrast imaging and in situ optical microscopy. Localized diffusible hydrogen in martensite causes cracking through two mechanisms: (1) interaction between {1 1 0}M localized slip and {1 1 2}M twin and (2) cracking of martensite-martensite grain interfaces. The former resulted in nanovoids along the {1 1 2}M twin. The coalescence of the nanovoids generated plate-like microvoids. The latter caused shear localization on the specific plane where the crack along the martensite/martensite boundary exists, which led to additional martensite/martensite boundary cracking. © 2015 Taylor & Francis.

Proton transfer processes play an important role in many fields of chemistry. In dilute basic aqueous solutions, proton transfer from water molecules to hydroxide ions is aided by "presolvation", i.e., thermal fluctuations that modify the hydrogen-bonding environment around the proton-receiving OH- ion to become more similar to that of a neutral H2O molecule. In particular at high concentrations, however, the underlying mechanisms and especially the role of the counterions are little understood. As a prototypical case, we investigate aqueous NaOH solutions using molecular dynamics simulations employing a reactive high-dimensional neural-network potential constructed from density functional theory reference data. We find that with increasing concentration the predominant proton transfer mechanism changes from being "acceptor-driven", i.e., governed by the presolvation of OH-, to "donor-driven", i.e., governed by the presolvation of H2O, and back to acceptor-driven near the room-temperature solubility limit of 19 mol/L, which corresponds to an extremely solvent-deficient system containing only about one H2O molecule per ion. Specifically, we identify concentration ranges where the proton transfer rate is mostly affected by OH- losing an accepted hydrogen bond, OH- forming a donated hydrogen bond, H2O forming an accepted hydrogen bond, or H2O losing a coordinated Na+. Presolvation also manifests itself in the shortening of the Na+-OH2 distances, in that the Na+ "pushes" one of the H2O protons away. © 2016 American Chemical Society.

Although the hydrogen evolution reaction (HER) is one of the fastest electrocatalytic reactions, modern polymer electrolyte membrane (PEM) electrolysers require larger platinum loadings (∼0.5-1.0 mg cm-2) than those in PEM fuel cell anodes and cathodes altogether (∼0.5 mg cm-2). Thus, catalyst optimization would help in substantially reducing the costs for hydrogen production using this technology. Here we show that the activity of platinum(111) electrodes towards HER is significantly enhanced with just monolayer amounts of copper. Positioning copper atoms into the subsurface layer of platinum weakens the surface binding of adsorbed H-intermediates and provides a twofold activity increase, surpassing the highest specific HER activities reported for acidic media under similar conditions, to the best of our knowledge. These improvements are rationalized using a simple model based on structure-sensitive hydrogen adsorption at platinum and copper-modified platinum surfaces. This model also solves a long-lasting puzzle in electrocatalysis, namely why polycrystalline platinum electrodes are more active than platinum(111) for the HER.

We propose the very first “Nernstian biosupercapacitor”, a biodevice based on only one redox polymer: poly(vinyl imidazole-co-allylamine)[Os(bpy)2Cl], and two biocatalysts. At the bioanode PQQ-dependent glucose dehydrogenase reduces the Os3+ moieties at the polymer to Os2+ shifting the Nernst potential of the Os3+/Os2+ redox couple to negative values. Concomitantly, at the biocathode the reduction of O2 by means of bilirubin oxidase embedded in the same redox polymer leads to the oxidation of Os2+ to Os3+ shifting the Nernst potential to higher values. Despite the use of just one redox polymer an open circuit voltage of more than 0.45 V was obtained during charging and the charge is stored in the redox polymer at both the bioanode and the biocathode. By connecting both electrodes via a predefined resistor a high power density is obtained for a short time exceeding the steady state power of a corresponding biofuel cell by a factor of 8. © 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

It is demonstrated that amorphous cobalt boride (Co2B) prepared by the chemical reduction of CoCl2 using NaBH4 is an exceptionally efficient electrocatalyst for the oxygen evolution reaction (OER) in alkaline electrolytes and is simultaneously active for catalyzing the hydrogen evolution reaction (HER). The catalyst achieves a current density of 10 mA cm(-2) at 1.61 V on an inert support and at 1.59 V when impregnated with nitrogen-doped graphene. Stable performance is maintained at 10 mA cm(-2) for at least 60 h. The optimized catalyst, Co2B annealed at 500 degrees C (Co2B-500) evolves oxygen more efficiently than RuO2 and IrO2, and its performance matches the best cobalt-based catalysts reported to date. Co2B is irreversibly oxidized at OER conditions to form a CoOOH surface layer. The active form of the catalyst is therefore represented as CoOOH/Co2B. EXAFS observations indicate that boron induces lattice strain in the crystal structure of the metal, which potentially diminishes the thermodynamic and kinetic barrier of the hydroxylation reaction, formation of the OOH* intermediate, a key limiting step in the OER.

A correct description of hydrogen diffusion and trapping is the prerequisite for an understanding of the phenomenon of hydrogen embrittlement. In this study, we carried out extensive first-principles calculations based on density functional theory to investigate the interaction of H with TiC precipitates that are assumed to be efficient trapping agents mitigating HE in advanced high-strength steels. We found that there exists a large variety of possible trapping sites for H associated with different types of interfaces between the TiC particle and the Fe matrix, with misfit dislocations and other defects at these interfaces, and with carbon vacancies in TiC. The most efficient trapping by more than 1 eV occurs at carbon vacancies in the interior of TiC particles. However, these traps are difficult to populate at ambient temperatures since the energy barrier for H entering the particles is high. H trapping at the semicoherent interfaces between the TiC particles and the Fe matrix is moderate, ranging from 0.3 to 0.5 eV. However, a sufficiently large concentration of the carbide particles can significantly reduce the amount of H segregated at dislocation cores in the Fe matrix. A systematic comparison of the obtained theoretical results with available experimental observations reveals a consistent picture of hydrogen trapping at the TiC particles that is expected to be qualitatively valid also for other carbide precipitates with the rock-salt crystal structure. © 2016 American Physical Society.

The cyclic voltammetric responses of individual palladium-coated carbon nanotubes are reported. Upon impact - from the solution phase - with the electrified interface, the nanoparticles act as individual nanoelectrodes catalyzing the hydrogen-oxidation reaction. At high overpotentials the current is shown to reach a quasi-steady-state diffusion limit, allowing determination of the tube length. The electrochemical response of the individual nanotubes also reveals the system to be modulated by the electrical contact between the electrode and carbon nanotube. This modulation presents itself as fluctuations in the recorded Faradaic current. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The influence of Ti on hydrogen diffusion and trapping in various advanced high strength steels was investigated. Electrochemical hydrogen permeation tests were performed on various model steels, with and without Ti, with benchmark tests performed using a commercial steel variant. The hydrogen trapping parameters for each steel were determined by fitting the permeation curves with a finite element model based on the McNabb and Foster equations using least squares minimisation. The influence of Ti on the hydrogen trapping parameters was greatly dependent on microstructure, with ferrite-containing grades being most affected. The results are inconsistent with hydrogen trapping by TiC particles, but consistent with trapping by boundaries between neighbouring ferrite and martensite grains. © 2015 Elsevier Ltd.

The elastic dipole tensor is a fundamental quantity relating the elastic field and atomic structure of a point defect. We review three methods in the literature to calculate the dipole tensor and apply them to hydrogen in α-zirconium using density functional theory (DFT). The results are compared with the dipole tensor deduced from earlier experimental measurements of the λ tensor for hydrogen in α-zirconium. There are significant errors with all three methods. We show that calculation of the λ tensor, in combination with experimentally measured elastic constants and lattice parameters, yields dipole tensor components that differ from experimental values by only 10%-20%. There is evidence to suggest that current state-of-the-art DFT calculations underestimate bonding between hydrogen and α-zirconium. © 2016 American Physical Society.

Protein film electrochemistry (PFE) has been used to study the assembly of the complex 6Fe active site of [FeFe]-hydrogenases (known as the H-cluster) from its precursors - the [4Fe-4S] domain that is already coordinated within the host, and the 2Fe domain that is presented as a synthetic water-soluble complex stabilized by an additional CO. Not only does PFE allow control of redox states via the electrode potential but also the immobilized state of the enzyme facilitates control of extremely low concentrations of the 2Fe complex. Results for two enzymes, CrHydA1 from Chlamydomonas reinhardtii and CpI from Clostridium pasteurianum, are very similar, despite large differences in size and structure. Assembly begins with very tight binding of the 34-valence electron 2Fe complex to the apo-[4Fe-4S] enzyme, well before the rate-determining step. The precursor is trapped under highly reducing conditions (<-0.5 V vs SHE) that prevent fusion of the [4Fe-4S] and 2Fe domains (via cysteine-S) since the immediate product would be too electron-rich. Relaxing this condition allows conversion to the active H-cluster. The intramolecular steps are relevant to the final stage of biological H-cluster maturation. © 2016 American Chemical Society.

In this work we have studied transgranular cleavage and the fracture toughness of titanium hydrides by means of quantum mechanical calculations based on density functional theory. The calculations show that the surface energy decreases and the unstable stacking fault energy increases with increasing hydrogen content. This is consistent with experimental findings of brittle behaviour of titanium hydrides at low temperatures. Based on Griffith-Irwin theory we estimate the fracture toughness of the hydrides to be of the order of 1 MPa⋅m1/2, which concurs well with experimental data. To investigate the cleavage energetics, we analyse the decohesion at various crystallographic planes and determine the traction-separation laws based on the Rose's extended universal binding energy relation. The calculations predict that the peak stresses do not depend on the hydrogen content of the phases, but it is rather dependent on the crystallographic cleavage direction. However, it is found that the work of fracture decreases with increasing hydrogen content, which is an indication of hydrogen induced bond weakening in the material. © 2016 Acta Materialia Inc.

In plants, algae, and cyanobacteria, photosystem 2 (PS2) catalyzes the light driven oxidation of water. The main products of this reaction are protons and molecular oxygen. In vitro, however, it was demonstrated that reactive oxygen species like hydrogen peroxide are obtained as partially reduced side products. The transition from oxygen to hydrogen peroxide evolution might be induced by light triggered degradation of PS2’s active center. Herein, the authors propose an analytical approach to investigate light induced bioelectrocatalytic processes such as PS2 catalyzed water splitting. By combining chronoamperometry and fluorescence microscopy, the authors can simultaneously monitor the photocurrent and the hydrogen peroxide evolution of light activated, solvent exposed PS2 complexes, which have been immobilized on a functionalized gold electrode. The authors show that under limited electron mediation PS2 displays a lower photostability that correlates with an enhanced H2O2 generation as a side product of the light induced water oxidation. © 2015 American Vacuum Society.

The need for sustainable catalysts for an efficient hydrogen evolution reaction is of significant interest for modern society. Inspired by comparable structural properties of [FeNi]-hydrogenase, here we present the natural ore pentlandite (Fe 4.5 Ni 4.5 S 8) as a direct rock' electrode material for hydrogen evolution under acidic conditions with an overpotential of 280 mV at 10 mA cm -2. Furthermore, it reaches a value as low as 190 mV after 96 h of electrolysis due to surface sulfur depletion, which may change the electronic structure of the catalytically active nickel-iron centres. The rock' material shows an unexpected catalytic activity with comparable overpotential and Tafel slope to some well-developed metallic or nanostructured catalysts. Notably, the rock' material offers high current densities (≤650 mA cm -2) without any loss in activity for approximately 170 h. The superior hydrogen evolution performance of pentlandites as rock' electrode labels this ore as a promising electrocatalyst for future hydrogen-based economy.

A simple and scalable method for synthesizing Co3O4nanoparticles supported on the framework of mesoporous carbon (MC) was developed. Benefiting from an ion-exchange process during the preparation, the cobalt precursor is introduced into a mesostructured polymer framework that results in Co3O4nanoparticles (ca. 3 nm) supported on MC (Co3O4/MC) with narrow particle size distribution and homogeneous dispersion after simple reduction/pyrolysis and mild oxidation steps. The as-obtained Co3O4/MC is a highly efficient catalyst for transfer hydrogenation of α,β-unsaturated aldehydes. Selectivities towards unsaturated alcohols are always higher than 95 % at full conversion. In addition, the Co3O4/MC shows high stability under the reaction conditions, it can be recycled at least six times without loss of activity. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Cu–Co-based catalysts derived from hydrotalcite (HT)-type precursors were applied in higher alcohol synthesis (HAS) at 280 °C, 60 bar and a H2/CO ratio of 1/1. Catalysts with higher Cu/Co ratios were found to provide the best trade-off between selective alcohol formation and moderate Fischer–Tropsch synthesis (FTS) activity. Within the alcohols and hydrocarbons formed the productivities decreased exponentially with increasing chain length according to the ASF distribution indicating a chain growth mechanism. Thermal analysis revealed the presence of different bivalent cations in one single HT-type precursor phase. After calcination at lower temperatures (Tcalc <  600 °C) a carbonate-modified ZnAl2O4 matrix was obtained. Within this amorphous matrix Cu2+ and Co2+ were found to be partially embedded resulting in an impeded ion reduction. After HAS the presence of bulk Co2C was detected by XRD. Both close contact of Cu0 and Co0 as well as Co2C–Co0 interfaces are known to provide the mechanistic requirements for higher alcohol formation. For comparison HAS was performed over a physical mixture consisting of the Al-containing HTs of Cu, Co or Zn. For the simultaneously co-precipitated samples the major roles of Cu are to decrease the FTS activity of metallic Co and to lower the alcohol chain growth probability by intimate Cu0–Co0 interactions. With increasing Cu content the alcohol selectivities were found to increase at the expense of high conversion, with ethanol being the major oxygenate product for all HT-based catalysts. © 2016, Springer Science+Business Media New York.

The [FeFe]-hydrogenase HYDA1 from Chlamydomonas reinhardtii is particularly amenable to biochemical and biophysical characterization because the H-cluster in the active site is the only inorganic cofactor present. Herein, we present the complete chemical incorporation of the H-cluster into the HYDA1-apoprotein scaffold and, furthermore, the successful replacement of sulfur in the native [4FeH] cluster with selenium. The crystal structure of the reconstituted pre-mature HYDA1[4Fe4Se]Hprotein was determined, and a catalytically intact artificial H-cluster variant was generated upon in vitro maturation. Full hydrogen evolution activity as well as native-like composition and behavior of the redesigned enzyme were verified through kinetic assays, FTIR spectroscopy, and X-ray structure analysis. These findings reveal that even a bioinorganic active site with exceptional complexity can exhibit a surprising level of compositional plasticity. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The redox competition mode of scanning electrochemical microscopy (SECM) was used to visualize differences in local electrocatalytic activity of Fe and Ni hexacyanoferrates (HCFs) in hydrogen peroxide reduction. The uniform round-shaped spots of electrocatalysts for the SECM measurements were electrochemically deposited using a scanning droplet cell. A negligible activity of NiHCF towards H2O2 reduction compared to Prussian Blue (PB) was observed. The dependence of local Prussian Blue activity on the applied potential was investigated. The proposed strategy explores the potential application of SECM as a rapid screening tool for HCF film activity within a single experiment. © 2016, Pleiades Publishing, Ltd.

Low-cost electrocatalysts based on highly dispersed molybdenum carbide supported on carbon nanotubes (CNTs) were developed for the hydrogen evolution reaction (HER). The synthesis of MoxC/CNT was achieved by impregnation using ammonium heptamolybdate followed by a thermal treatment at 700 °C in CH4/H2, H2 or N2. The composites were characterized by X-ray diffraction, N2 physisorption, and X-ray photoelectron spectroscopy. β-Mo2C was the main Mo carbide phase generated in N2 or H2, whereas α-MoC was the dominant phase formed in CH4/H2. All the MoxC/CNT composites were catalytically active in the HER under alkaline conditions. The catalyst pretreated in pure H2 exhibited the highest HER activity, which was found to correlate with a higher amount of Mo2C, a higher total Mo content and a higher Mo surface concentration compared with the other two less active samples. Amorphous carbon on the surface seems to play an important role in limiting the HER performance of the Mo carbide catalysts, and the treatment in H2 removed it most effectively leading to high HER activity. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Water in contact with mineral interfaces is important for a variety of different processes. Here, we present a combined theoretical/experimental study which provides a quantitative, molecular-level understanding of the ubiquitous and important CaF 2 /water interface. Our results show that, at low pH, the surface is positively charged, causing a substantial degree of water ordering. The surface charge originates primarily from the dissolution of fluoride ions, rather than from adsorption of protons to the surface. At high pH we observe the presence of Ca-OH species pointing into the water. These OH groups interact remarkably weakly with the surrounding water, and are responsible for the free OH signature in the VSFG spectrum, which can be explained from local electronic structure effects. The quantification of the surface termination, near-surface ion distribution and water arrangement is enabled by a combination of advanced phase-resolved Vibrational Sum Frequency Generation spectra of CaF 2 /water interfaces and state-of-the-art ab initio molecular dynamics simulations which include electronic structure effects.

Whereas the interactions between water molecules are dominated by strongly directional hydrogen bonds (HBs), it was recently proposed that relatively weak, isotropic van der Waals (vdW) forces are essential for understanding the properties of liquid water and ice. This insight was derived from ab initio computer simulations, which provide an unbiased description of water at the atomic level and yield information on the underlying molecular forces. However, the high computational cost of such simulations prevents the systematic investigation of the influence of vdW forces on the thermodynamic anomalies of water. Here, we develop efficient ab initio-quality neural network potentials and use them to demonstrate that vdW interactions are crucial for the formation of water's density maximum and its negative volume of melting. Both phenomena can be explained by the flexibility of the HB network, which is the result of a delicate balance of weak vdW forces, causing, e.g., a pronounced expansion of the second solvation shell upon cooling that induces the density maximum.

Synthetic composite materials that mimic the structure and composition of mammalian tooth enamel were prepared by mixing fluoroapatite rods (diameter 2-3 μm, thickness about 0.5 μm) and methylmethacrylate (MMA), followed by polymerization either during or immediately after ultracentrifugation, using either a tertiary amine/radical initiator for polymerization at room temperature or a radical initiator for thermal polymerization. This led to mineral-rich composites (mineral content between 50 and 75 wt%). To enhance the mechanical stability and the interaction between fluoroapatite and polymer matrix, small amounts of differently functionalized MMA monomers were added to the co-monomer mixture. Another approach was the coating of the fluoroapatite rods with silica and the polymerization in the presence of a siloxane-functionalized MMA monomer. The hardness of the composites was about 0.2-0.4 GPa as determined by Vickers indentation tests, about 2 times higher than the polymer matrix alone. The composites had a good resistance against acids (60 min at pH 3, 37 °C). © 2016 IOP Publishing Ltd.

Non-noble metal based materials efficiently catalyzing the hydrogen evolution reaction (HER) are reported based on a novel strategy where electrocatalytically active ultrathin molybdenum sulphoselenide sheets are incorporated into electrically conducting reduced graphene oxide sheets via a self-assembly approach. By taking advantage of the electrostatic attraction between the two oppositely charged nanosheets, MoSSe@rGO composite materials are obtained exhibiting superior electrocatalytic activity and stability for the HER allowing a current density of 5 mA cm−2 at a low overpotential of only 135 mV. These findings pave the way to novel electrocatalysts based on composites of MoSSe and reduced graphene oxide towards the design of ultra-light, mechanically robust and electrically conductive electrode materials for electrocatalytic water splitting. © 2016 Elsevier Ltd

The six-iron cofactor of [FeFe]-hydrogenases (H-cluster) is the most efficient H2-forming catalyst in nature. It comprises a diiron active site with three carbonmonoxide (CO) and two cyanide (CN-) ligands in the active oxidized state (Hox) and one additional CO ligand in the inhibited state (Hox-CO). The diatomic ligands are sensitive reporter groups for structural changes of the cofactor. Their vibrational dynamics were monitored by real- Time attenuated total reflection Fouriertransform infrared spectroscopy. Combination of 13CO gas exposure, blue or red light irradiation, and controlled hydration of three different [FeFe]-hydrogenase proteins produced 8 Hox and 16 Hox-CO species with all possible isotopic exchange patterns. Extensive density functional theory calculations revealed the vibrational mode couplings of the carbonyl ligands and uniquely assigned each infrared spectrum to a specific labeling pattern. For Hox-CO, agreement between experimental and calculated infrared frequencies improved by up to one order of magnitude for an apical CN- At the distal iron ion of the cofactor as opposed to an apical CO. For Hox, two equally probable isomers with partially rotated ligands were suggested. Interconversion between these structures implies dynamic ligand reorientation at the H-cluster. Our experimental protocol for site-selective 13CO isotope editing combined with computational species assignment opens new perspectives for characterization of functional intermediates in the catalytic cycle.

The single-step production of wax-free liquid hydrocarbons from syngas (H2 + CO) via integration of Fischer-Trospch (FT) and hydrocracking catalysts represents an attractive approach toward process intensification in compact gas-to-liquid technologies. Despite current, intensive efforts on the development of hybrid (multifunctional) catalysts to this end, not much is known about the reactivity of different FT primary products on hydrocracking catalysts under syngas. Using model compounds, the individual and collective reactivities of n-paraffin and α-olefin FT primary products were systematically studied on a Pt/nano-H-ZSM-5 hydrocracking catalyst under H2 (standard hydrocracking) and syngas (in situ hydroprocessing) atmospheres. Under H2, both reactants show indistinguishable reactivity as rapid olefin hydrogenation precedes hydrocracking. Under syngas, however, inhibition of (de)hydrogenation functionalities by CO poisoning of metal sites leads to a notable divergence of the reaction pathways for n-paraffins and α-olefins. Under these conditions, α-olefins showed enhanced reactivity, as an initial dehydrogenative activation step is not required, and contributed to moderate secondary cracking, likely via enhanced competitive adsorption on the acid sites. Besides, CO poisoning restored the intrinsic activity of the zeolite for the oligomerization of short-chain (α-)olefins, providing an additional net chain-growth pathway, which contributes to reducing the overall yield to undesired gas (C4-) hydrocarbons. These findings emphasize the key role of not only the chain-length distribution, but also the olefinic content of the FT primary hydrocarbons for the ultimate product distribution, and suggest guidelines for the design of multifunctional catalysts for the single-step synthesis of liquid hydrocarbons from syngas. © 2016 American Chemical Society.

Multistep synthesis and electrochemical characterization of an Os complex-modified redox hydrogel exhibiting a redox potential ≈+30 mV (vs. Ag/AgCl 3 m KCl) is demonstrated. The careful selection of bipyridine-based ligands bearing N,N-dimethylamino moieties and an amino-linker for the covalent attachment to the polymer backbone ensures the formation of a stable redox polymer with an envisaged redox potential close to 0 V. Most importantly, the formation of an octahedral N6-coordination sphere around the Os central atoms provides improved stability concomitantly with the low formal potential, a low reorganization energy during the Os3+/2+ redox conversion and a negligible impact on oxygen reduction. By wiring a variety of enzymes such as pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase, flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase and the FAD-dependent dehydrogenase domain of cellobiose dehydrogenase, low-potential glucose biosensors could be obtained with negligible co-oxidation of common interfering compounds such as uric acid or ascorbic acid. In combination with a bilirubin oxidase-based biocathode, enzymatic biofuel cells with open-circuit voltages of up to 0.54 V were obtained. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The impact of the alkali metal cations (Li+, Na+, K+, Rb+, Cs+) on the catalytic activity of Pt(1 1 1) electrodes towards model reactions (oxygen reduction, oxygen evolution, hydrogen evolution and hydrogen oxidation) in sulfuric acid has been evaluated. In contrast to essentially monotonic activity trends (i.e. from Li+ to Cs+) reported in the literature for alkaline media, the nature of the cations influences the activity of the Pt electrodes largely non-monotonously in the presence of SO4 2- ions. This is in certain cases due to the specifically adsorbing (bi)sulfate anions which make interactions between electrolyte components and reaction intermediates very complex. Surprisingly, the activity of the Pt(1 1 1) electrodes towards all investigated electrocatalytic reactions was substantially higher in Rb+ ions containing electrolytes. © 2014 Elsevier B.V. All rights reserved.

Partial reversion of interlath austenite nano-films is investigated as a potential remedy for hydrogen embrittlement susceptibility of martensitic steels. We conducted uniaxial tensile tests on hydrogen-free and pre-charged medium-Mn transformation-induced plasticity-maraging steels with different austenite film thicknesses. Mechanisms of crack propagation and microstructure interaction are quantitatively analyzed using electron channelling contrast imaging and electron backscatter diffraction, revealing a promising strategy to utilize austenite reversion for hydrogen-resistant martensitic steel design. © 2015, The Minerals, Metals & Materials Society and ASM International.

The [FeFe] hydrogenase is a highly sophisticated enzyme for the synthesis of hydrogen via a biological route. The rotated state of the H-cluster in the [FeIFeI] form was found to be an indispensable criteria for an effective catalysis. Mimicking the specific rotated geometry of the [FeFe] hydrogenase active site is highly challenging as no protein stabilization is present in model compounds. In order to simulate the sterically demanding environment of the nature's active site, the sterically crowded meso-bis(benzylthio)diphenylsilane (2) was utilized as dithiolate linker in an [2Fe2S] model complex. The reaction of the obtained hexacarbonyl complex 3 with 1,2-bis(dimethylphosphino)ethane (dmpe) results three different products depending on the amount of dmpe used in this reaction: [{Fe2(CO)5{μ-(SCHPh)2SiPh2}}2(μ-dmpe)] (4), [Fe2(CO)5(κ2-dmpe){μ-(SCHPh)2SiPh2}] (5) and [Fe2(CO)5(μ-dmpe){μ-(SCHPh)2SiPh2}] (6). Interestingly, the molecular structure of compound 5 shows a [FeFe] subsite comprising a semi-rotated conformation, which was fully characterized as well as the other isomers 4 and 6 by elemental analysis, IR and NMR spectroscopy, X-ray diffraction analysis (XRD) and DFT calculations. The herein reported model complex is the first example so far reported for [FeIFeI] hydrogenase model complex showing a semi-rotated geometry without the need of stabilization via agostic interactions (Fe⋯H-C). This journal is © The Royal Society of Chemistry.

We present a combined experimental sum-frequency generation (SFG) spectroscopy and ab initio molecular dynamics simulations study to clarify the structure and orientation of water at zwitterionic phosphatidylcholine (PC) lipid and amine N-oxide (AO) surfactant monolayers. Simulated O-H stretch SFG spectra of water show good agreement with the experimental data. The SFG response at the PC interface exhibits positive peaks, whereas both negative and positive bands are present for the similar zwitterionic AO interface. The positive peaks at the water/PC interface are attributed to water interacting with the lipid carbonyl groups, which act as efficient hydrogen bond acceptors. This allows the water hydrogen bond network to reach, with its (up-oriented) O-H groups, into the headgroup of the lipid, a mechanism not available for water underneath the AO surfactant. This highlights the role of the lipid carbonyl group in the interfacial water structure at the membrane interface, namely, stabilizing the water hydrogen bond network. © 2015 American Chemical Society.

The hydrogen oxidation reaction was studied at bright polycrystalline platinum microelectrodes. A smaller steady-state current was observed in experiment as compared to that anticipated for a diffusion limited process. To facilitate physical insight into this system, a simulation model based on the Tafel-Volmer mechanism for the hydrogen oxidation reaction was developed. Under conditions of reversible electron transfer, the adsorption kinetics ka and kd are found to have distinctly different influences upon the voltammetry responses. Correspondence between the simulated and the experimental voltammograms is found, confirming the decrease of the steady-state current is caused by the slow adsorption process. The combined adsorption parameter kaγmax2 on the Tafel-Volmer mechanism was approximately 5.0 × 10-4 m s-1, where γ max (mol m-2) is the maximum surface coverage of adsorption hydrogen atoms. © 2015 American Chemical Society.

Investigating the properties of protons in water is essential for understanding many chemical processes in aqueous solution. While important insights can in principle be gained by accurate and well-established methods like ab initio molecular dynamics simulations, the computational costs of these techniques are often very high. This prevents studying large systems on long time scales, which is severely limiting the applicability of computer simulations to address a wide range of interesting phenomena. Developing more efficient potentials enabling the simulation of water including dissociation and recombination events with first-principles accuracy is a very challenging task. In particular protonated water clusters have become important model systems to assess the reliability of such potentials, as the presence of the excess proton induces substantial changes in the local hydrogen bond patterns and many energetically similar isomers exist, which are extremely difficult to describe. In recent years it has been demonstrated for a number of systems including neutral water clusters of varying size that neural networks (NNs) can be used to construct potentials with close to first-principles accuracy. Based on density-functional theory (DFT) calculations, here we present a reactive full-dimensional NN potential for protonated water clusters up to the octamer. A detailed investigation of this potential shows that the energetic, structural, and vibrational properties are in excellent agreement with DFT results making the NN approach a very promising candidate for developing a high-quality potential for water. This finding is further supported by first preliminary but very encouraging NN-based simulations of the bulk liquid. This journal is © the Owner Societies 2015.

We report on a biophotocathode based on photosystem 1 (PS1)-Pt nanoparticle complexes integrated in a redox hydrogel for photoelectrocatalytic H2 evolution at low overpotential. A poly(vinyl)imidazole Os(bispyridine)2Cl polymer serves as conducting matrix to shuttle the electrons from the electrode to the PS1-Pt complexes embedded within the hydrogel. Light induced charge separation at the PS1-Pt complexes results in the generation of photocurrents (4.8 ± 0.4 μA cm-2) when the biophotocathodes are exposed to anaerobic buffer solutions. Under these conditions, the protons are the sole possible electron acceptors, suggesting that the photocurrent generation is associated with H2 evolution. Direct evidence for the latter process is provided by monitoring the H2 production with a Pt microelectrode in scanning electrochemical microscopy configuration over the redox hydrogel film containing the PS1-Pt complexes under illumination. © 2015 American Chemical Society.

We present azimuth- and polarization-dependent infrared spectroscopy results obtained under ultra-high vacuum conditions on surface species formed by the interaction of formic acid with the mixed-terminated ZnO(101¯0) surface. Since there are no previous IRRAS data for formic-acid derived species on any ZnO single crystal surfaces, we have carried out calculations using density function theory to aid the interpretation of the results. From our combined experimental and theoretical data we conclude that two different formate species are formed. The more strongly bound species is a bidentate with the formate molecular plane oriented along the [12¯10] direction. The less strongly bound species is a quasi-bidentate with its molecular plane oriented along the [0001] direction. This second species is characterized by a strong hydrogen bond between a surface OH species and the formate. In addition, IR data were recorded for the same molecule adsorbed on commercial ZnO nanoparticles. The different bands of the powder IR-data are assigned on the basis of the experimental and theoretical results obtained for the single crystal surface. This study demonstrates the importance of the Surface Science approach to heterogeneous catalysis also for ZnO, an important catalyst for the conversion of syngas to methanol. © 2014 Springer Science+Business Media.

The hydrogen distribution in a hydrogen-charged Fe-18Mn-1.2C (wt%) twinning-induced plasticity austenitic steel was studied by Scanning Kelvin Probe Force Microscopy (SKPFM). We observed that 1-2 days after the hydrogen-charging, hydrogen showed a higher activity at twin boundaries than inside the matrix. This result indicates that hydrogen at the twin boundaries is diffusible at room temperature, although the twin boundaries act as deeper trap sites compared to typical diffusible hydrogen trap sites such as dislocations. After about 2 weeks the hydrogen activity in the twin boundaries dropped and was indistinguishable from that in the matrix. These SKPFM results were supported by thermal desorption spectrometry and scanning electron microscopic observations of deformation-induced surface cracking parallel to deformation twin boundaries. With this joint approach, two main challenges in the field of hydrogen embrittlement research can be overcome, namely, the detection of hydrogen with high local and chemical sensitivity and the microstructure-dependent and spatially resolved observation of the kinetics of hydrogen desorption. © 2015 The Electrochemical Society.

The current energy system is subject to a profound change: A system, designed to cater to energy needs by supplying fossil fuels is now expected to shift to integrate ever larger amounts of renewable energies to achieve overall a more sustainable energy supply. The challenges arising from this paradigm change are currently most obvious in the area of electric power supply. However, it affects the entire energy system, albeit with different effects. Within the energy system, various independent grids fulfill the function to transport and distribute energy or energy carriers in order to address spatially different energy supply and demand situations. Temporal variations are currently addressed by just-in-time production of the required energy form. However, renewable energy sources generally supply their energy independently from any specific energy demand. Their contribution to the overall energy system is expected to increase significantly. Energy storage technologies also represent an option to compensate for a temporal difference in energy supply and demand. Energy storage systems have the ability for a controlled take-up of a certain amount of energy, storing this energy within a storage media on a relevant timescale and a controlled redispatch of the energy after a certain time delay. Energy storage systems can also be constructed as process chains by combinations of unit operations, each covering different aspects of those functions. Large-scale mechanical storage options for electrical power are currently almost exclusively pumped hydro storage. These systems might be complemented in the future by compressed-air storage and maybe liquid-air facilities. There are several electrochemical storage technologies currently under investigation for their suitability as large scale electrical energy storage in various stages of research, development, and demonstration. Thermal energy storage technologies are based on a large variety of storage principles: Sensible heat, latent heat (based on phase transitions), adsorption/desorption processes or on chemical reactions. The latter can be a route to permanent and loss-free storage of heat. Chemical energy storage systems are based on the energy contained within the chemical bonds of the respective storage molecules. These storage molecules can act as energy carriers. Equally well, these compounds can enter various industrial value chains in energy-intensive industrial sectors and are therefore in direct economic competition with established (fossil) supply routes for these compounds. Water electrolysis, producing hydrogen and oxygen, is and will be the key technology for the foreseeable future. Hydrogen can be transformed by various processes to other energy carriers of interest. These transformations make the stored energy accessible by different sectors of the energy system and/or as raw materials for energy-intensive industrial processes. Some functions of energy storage systems can be taken over by industrial processes. Within the overall energy system, chemical energy storage technologies open up opportunities to link, connect and interweave the various energy streams and sectors. While chemical energy storage offers a route for a stronger integration of renewable energy outside the power sector, it also creates new opportunities for increased flexibility, novel synergies and additional optimization. Several examples of specific energy utilization are discussed and evaluated with respect to energy storage applications. © 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Ab initio molecular dynamics (AIMD) simulations in trimethylamine N-oxide (TMAO)-D2O solution are employed to elucidate the effects of TMAO on the reorientational dynamics of D2O molecules. By decomposing the O-D groups of the D2O molecules into specific subensembles, we reveal that water reorientational dynamics are retarded considerably in the vicinity of the hydrophilic TMAO oxygen (OTMAO) atom, due to the O-D···OTMAO hydrogen-bond. We find that this reorientational motion is governed by two distinct mechanisms: The O-D group rotates (1) after breaking the O-D···OTMAO hydrogen-bond, or (2) together with the TMAO molecule while keeping this hydrogen-bond intact. While the orientational slow-down is prominent in the AIMD simulation, simulations based on force field models exhibit much faster dynamics. The simulated angle-resolved radial distribution functions illustrate that the O-D···OTMAO hydrogen-bond has a strong directionality through the sp3 orbital configuration in the AIMD simulation, and this directionality is not properly accounted for in the force field simulation. These results imply that care must be taken when modeling negatively charged oxygen atoms as single point charges; force field models may not adequately describe the hydration configuration and dynamics. © 2015 American Chemical Society.

The proliferation of fibroblasts and myofibroblast differentiation are crucial in wound healing and wound closure. Impaired wound healing is often correlated with chronic bacterial contamination of the wound area. A new promising approach to overcome wound contamination, particularly infection with antibiotic-resistant pathogens, is the topical treatment with non-thermal “cold” atmospheric plasma (CAP). Dielectric barrier discharge (DBD) devices generate CAP containing active and reactive species, which have antibacterial effects but also may affect treated tissue/cells. Moreover, DBD treatment acidifies wound fluids and leads to an accumulation of hydrogen peroxide (H2O2) and nitric oxide products, such as nitrite and nitrate, in the wound. Thus, in this paper, we addressed the question of whether DBD-induced chemical changes may interfere with wound healing-relevant cell parameters such as viability, proliferation and myofibroblast differentiation of primary human fibroblasts. DBD treatment of 250 μl buffered saline (PBS) led to a treatment time-dependent acidification (pH 6.7; 300 s) and coincidently accumulation of nitrite (~300 μM), nitrate (~1 mM) and H2O2 (~200 μM). Fibroblast viability was reduced by single DBD treatments (60–300 s; ~77–66%) or exposure to freshly DBD-treated PBS (60–300 s; ~75–55%), accompanied by prolonged proliferation inhibition of the remaining cells. In addition, the total number of myofibroblasts was reduced, whereas in contrast, the myofibroblast frequency was significantly increased 12 days after DBD treatment or exposure to DBD-treated PBS. Control experiments mimicking DBD treatment indicate that plasma-generated H2O2 was mainly responsible for the decreased proliferation and differentiation, but not for DBD-induced toxicity. In conclusion, apart from antibacterial effects, DBD/CAP may mediate biological processes, for example, wound healing by accumulation of H2O2. Therefore, a clinical DBD treatment must be well-balanced in order to avoid possible unwanted side effects such as a delayed healing process.

The use of synthetic inorganic complexes as supported catalysts is a key route in energy production and in industrial synthesis. However, their intrinsic oxygen sensitivity is sometimes an issue. Some of us have recently demonstrated that hydrogenases, the fragile but very efficient biological catalysts of H2 oxidation, can be protected from O2 damage upon integration into a film of a specifically designed redox polymer. Catalytic oxidation of H2 produces electrons which reduce oxygen near the film/solution interface, thus providing a self-activated protection from oxygen [Plumeré et al., Nat Chem. 2014, 6, 822-827]. Here, we rationalize this protection mechanism by examining the time-dependent distribution of species in the hydrogenase/polymer film, using measured or estimated values of all relevant parameters and the numerical and analytical solutions of a realistic reaction-diffusion scheme. Our investigation sets the stage for optimizing the design of hydrogenase-polymer films, and for expanding this strategy to other fragile catalysts. © 2015 American Chemical Society.

The integration of sensitive catalysts in redox matrices opens up the possibility for their protection from deactivating molecules such as O2. [FeFe]-hydrogenases are enzymes catalyzing H2 oxidation/production which are irreversibly deactivated by O2. Therefore, their use under aerobic conditions has never been achieved. Integration of such hydrogenases in viologen-modified hydrogel films allows the enzyme to maintain catalytic current for H2 oxidation in the presence of O2, demonstrating a protection mechanism independent of reactivation processes. Within the hydrogel, electrons from the hydrogenase-catalyzed H2 oxidation are shuttled to the hydrogel-solution interface for O2 reduction. Hence, the harmful O2 molecules do not reach the hydrogenase. We illustrate the potential applications of this protection concept with a biofuel cell under H2/O2 mixed feed. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The proton/hydrogen redox couple underpins the electrochemical sciences; however, the nonunity stoichiometry of the reaction leads to distinct voltammetric complications. This Article provides a joint analytical, numerical, and experimental investigation into the reversible hydrogen evolution reaction at a platinum microelectrode. Literature obscurities and nuances are highlighted and corrected, allowing the presentation of an holistic overview of the electrochemical reaction at the reversible limit. Under such conditions, it is demonstrated, first, how the reaction may be misinterpreted as being irreversible and, second, that the transfer coefficient for the reversible (Nernstian) hydrogen evolution reaction is equal to 2. Importantly, the use of the reversible hydrogen electrode (RHE) as a reference potential in voltammetric experiments is critically evaluated. © 2015 American Chemical Society.

A test procedure for alkali-free Cu-Co-based catalysts synthesized by co-precipitation was established allowing the fast assessment and screening of their catalytic properties in the synthesis of higher alcohols by online GC analysis. Due to precisely controlled initial deactivation of the catalysts at 280 °C long-term measurements were avoided and steady-state conditions at 260 °C were reached within a short period of time. Temperatures up to 300 °C were found to favor the formation of methanol, whereas the product distribution was not affected at lower space velocities. Even traces of alkali ions present due to insufficient washing were found to strongly affect the catalytic properties. (Graph Presented). © Springer Science+Business Media 2015

The diffusion coefficients of interstitial hydrogen in bulk Fe and Ni crystals have been calculated over a wide range of temperatures employing first-principles methods based on density functional theory. Quantum mechanical effects have been included by means of the semiclassical transition state theory and the small-polaron model of Flynn and Stoneham. Our results show that to include such effects is crucial for a quantitative simulation of H diffusion in bcc Fe even at room temperature, while in the case of fcc Ni this is less important. The comparison with other theoretical approaches as well as with experimental studies emphasizes the main advantages of the present approach: it is quantitatively accurate and computationally efficient. © 2015 American Physical Society.

Abstract In this work, the interaction of hydrogen with high-angle GBs in nickel has been investigated by means of density functional theory simulations. Two distinct types of GBs have been considered: the Σ3(111)[1¯10] with a close-packed interface structure and the Σ5(210)[001] with a less dense interface structure consisting of open structural units. Our calculations reveal that these two GBs have a markedly different interaction behavior with atomic hydrogen. The close-packed Σ3 GB neither traps H nor enhances its diffusion, but instead acts as a two-dimensional diffusion barrier. In contrast, the Σ5 GB provides numerous trapping sites for H within the open structural units as well as easy migration pathways for H diffusion along the GB plane that can enhance the H diffusivity by about two orders of magnitude compared to bulk Ni. The obtained results are analysed in detail and compared with available experimental and other theoretical data. © 2015 Acta Materialia Inc.

Polycrystalline material generally exhibits degradation in its mechanical properties and shows more tendency for intergranular fracture due to segregation and diffusion of hydrogen on the grain boundaries (GBs). Understanding the parameters affecting the diffusion and binding of hydrogen within GBs will allow enhancing the mechanical properties of the commercial engineering materials and developing interface dominant materials. In practice during forming processes, the coincidence site lattice (CSL) GBs are experiencing deviations from their ideal configurations. Consequently, this will change the atomic structural integrity by superposition of sub-boundary dislocation networks on the ideal CSL interfaces. For this study, the ideal ∑ 3 111 [11 0] GB structure and its angular deviations in BCC iron within the range of Brandon criterion will be studied comprehensively using molecular statics (MS) simulations. The clean GB energy will be quantified, followed by the GB and free surface segregation energies calculations for hydrogen atoms. Rice-Wang model will be used to assess the embrittlement impact variation over the deviation angles. The results showed that the ideal GB structure is having the greatest resistance to embrittlement prior GB hydrogen saturation, while the 3° deviated GB is showing the highest susceptibility to embrittlement. Upon saturation, the 5° deviated GB appears to have the highest resistance instead due to the lowest stability of hydrogen atoms observed in the free surfaces of its simulation cell. Molecular dynamics (MD) simulations are then applied to calculate hydrogen diffusivity within the ideal and deviated GB structure. It is shown that hydrogen diffusivity decreases significantly in the deviated GB models. In addition, the 5° deviated GB is representing the local minimum for diffusivity results suggesting the existence of the highest atomic disorder and excessive secondary dislocation accommodation within this interface. Copyright © 2015 by ASME.

Coupling of redox-silent biocatalytic processes for analyte detection with enzyme-catalyzed redox reactions for signal generation is proposed by the modulation of electrostatic interactions between a pH-responsive polymer and a redox enzyme to control the off-on transition for electrochemical signal generation. Glassy carbon electrodes are modified with a poly(vinyl)imidazole Os(bipyridine)2Cl redox hydrogel film entrapping urease and PQQ-dependent glucose dehydrogenase, while glucose is present in the solution. The off-on transition is based on the detection of urea as model analyte which is hydrolyzed to ammonia by urease within the hydrogel film concomitantly increasing the local pH value thus invoking deprotonation of the imidazole groups at the polymer backbone. The decrease of positive charges at the polymer decreases electrostatic repulsion between the polymer and the positively charged PQQ-dependent glucose dehydrogenase. Hence, electron transfer rates between polymer-bound Os complexes and PQQ inside the enzyme are enhanced activating electrocatalytic oxidation of glucose. This process generates the electrochemical signal for urea detection. © 2014 Elsevier B.V.

Carbon nanotubes decorated with ultra-small metal nanoparticles are of great value in catalysis. We report that individual multiwalled carbon nanotubes decorated with ultra-small palladium nanoparticles can be detected by using the nano-impacts method. The high conductivity and reactivity of each decorated carbon nanotube is directly evidenced; this is achieved through studying the proton-reduction reaction for the underpotential deposition of hydrogen onto the nanoparticles decorated on the carbon nanotube walls. The reductive spikes from current amplification are analyzed to estimate the approximate length of the decorated carbon nanotubes, revealing that the decorated carbon nanotubes are electroactive along its entire length of several micrometers. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

An eggshell Mo2C catalyst which is designed from the rapid combination of molybdate with melamine is described. In contrast to Pd-based catalysts, the eggshell Mo2C operates effectively with a wide-concentration window in high-temperature gas phase hydrogenation of phenylacetylene, thus, an economical and energy-efficient front-end purification of styrene monomers might be possible. (c) 2015 American Institute of Chemical Engineers AIChE J, 61: 2522-2531, 2015

Earth-abundant materials are required to facilitate upscaling of renewable hydrogen generation. Here, the synthesis of a novel oxidic ternary cocatalyst containing molybdenum, chromium, and copper, which has been found to be highly active in the overall photocatalytic splitting of water over gallium oxide, is described. With the noble metal-free system, requiring hydrogen evolution rates comparable to that of the well-established RhxCr2-xO3/Ga2O3 water splitting cocatalyst is achieved. Although the stability of the as-prepared ternary cocatalyst system appeared to be poor, the cocatalyst can be easily regenerated and stabilized by an oxygen treatment under ambient conditions. Furthermore, higher MoOx loadings were found to be more active and showed improved stability. By means of careful characterization using X-ray-based spectroscopy and TEM, the function of the individual cocatalyst compounds was closely examined, suggesting synergetic interactions of molybdena and chromia stabilizing CuO against photoreduction. Although stability issues should be further addressed, this work highlights that multicomponent systems, which are well-studied in industrial processes for heterogeneous reactions and commonly used in various other fields of research, can be used in solar water splitting. In particular, molybdena-containing materials are discovered as a new class of earth-abundant cocatalysts for overall water-splitting. © 2015 American Chemical Society.

We explore co-deposition of water and 4, 4′-dihydroxy azobenzene on Ag(111) by low-temperature scanning tunneling microscopy at different water-to-azobenzene ratios. At all ratios, the water interacts with the hydroxyl end groups of the molecule replacing the direct hydrogen bonding. The change in bonding reduces the azobenzene density as compared to the one in the closed-packed waterless azobenzene structure. At intermediate water-to-azobenzene ratios, pores are formed in the azobenzene layer at nanometer distance from the water. At high water-to-azobenzene ratios, a water superstructure with a 1.4 nm × 1.4 nm unit cell develops. Our results point to a method to vary the density of an organic layer by tuning the amount of an inorganic additive. © 2015 AIP Publishing LLC.

Atomic layer-by-layer construction of Pd on nanoporous gold (NPG) has been investigated through the combination of underpotential deposition (UPD) with displacement reaction. It has been found that the UPD of Cu on NPG is sensitive to the applied potential and the deposition time. The optimum deposition potential and time were determined through potential- and time-sensitive stripping experiments. The NPG-Pd electrode shows a different voltammetric behavior in comparison to the bare NPG electrode, and the deposition potential was determined through the integrated charge control for the monolayer UPD of Cu on the NPG-Pd electrode. Five layers of Pd were constructed on NPG through the layer-by-layer deposition. In addition, the microstructure of the NPG-Pdx (x = 1, 2, 3, 4 and 5) films was probed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The microstructural observation demonstrates that the atomic layers of Pd form on the ligament surface of NPG through epitaxial growth, and have no effect on the nanoporous structure of NPG. In addition, the hydrogen storage properties of the NPG-Pdx electrodes have also been addressed. This journal is © The Royal Society of Chemistry.

Composites consisting of carbon nanotubes (CNTs) grown directly on oxygen-deficient anatase TiO2 (TiO2-δ) were synthesized by a two-step chemical vapor deposition (CVD) method and applied in photocatalytic hydrogen production from aqueous methanol solutions using photodeposited Pt as the co-catalyst. Thermogravimetry coupled with mass spectroscopy, X-ray diffraction, scanning electron microscopy, photocurrent analysis, X-ray photoelectron spectroscopy, and (scanning) transmission electron microscopy were performed to investigate the physical and (photo)chemical properties of the synthesized CNT-TiO2-δ composites before and after photocatalytic methanol reforming. The initial photocatalytic activity of TiO2 was found to be significantly improved in the presence of oxygen vacancies. An optimized amount (~7.2 wt%) of CNTs grown on the TiO2-δ surface led to a highly effective stabilization of the photocatalytic performance of TiO2 -δ, which is attributed to the improved dispersion and stability of the photodeposited Pt co-catalyst nanoparticles and enhanced separation efficiency of photogenerated electron-hole pairs, rendering the photocatalysts less prone to deactivation. © 2015, MDPI AG. All rights reserved.

Acetylene to butadiene direct synthesis, via enyne cross-metathesis, is demonstrated with commercial ruthenium carbene catalysts. Using excess of ethylene, yields greater than 50% are obtained. High activity is observed in the first minute of the reaction (TOF > 800 h-1 based on butadiene). Catalyst reusability and poisoning are discussed. This journal is © The Royal Society of Chemistry 2015.

La5.4WO12-delta(LaWO) is a promising membrane candidate for a variety of H-2-related applications due to its appreciable levels of mixed proton electron conduction and its stability in moist reducing atmospheres at elevated temperatures. Governed by Wagner theory, the H-2 permeation performance of a membrane can be enhanced by reducing its thickness. Therefore, the present work deals with preparing LaWO supported membranes with reduced thickness and optimised microstructure. Combining a dense membrane with a porous supporting layer is associated with mismatched sintering rates, which ultimately lead to bending effects. Therefore, the sintering behaviour of both the dense membrane and the porous substrate must be carefully adjusted to each other. For this purpose, single and co-fired membrane and substrate layers were produced by tape casting. Sintering experiments were carried out with an optical dilatometer. The shrinkage and microstructural evolution of the layers were evaluated in terms of the anisotropic shrinkage forces and the membrane rigidness counteracting the substrate shrinkage. The results were used to develop asymmetric LaWO membranes with optimal microstructure. High membrane density was combined with a substrate porosity of similar to 30% and minimised bending (40 pm). The LaWO membrane-substrate assembly displayed a He leakage of 10(-5) hPa dm(3), cm(-2) s(-1), which is a value that satisfies further practical demands. (C) 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license.

A simple model of the hydrogen desorption kinetics of metal hydrides is formulated and solved analytically. The particle surface reaction is assumed to be a rate-controlling-step. Then a volumetric measurement of hydrogen desorption process is evaluated on an example of wet ball milled magnesium hydride, and can be applied generally for any metal hydride. The solution reproduces the shape of experimental curves for desorption process. In the case of surface-controlled kinetics, a volumetric measurement requires a special evaluation of results, predicted by the solution of the model. An improved evaluation of the volumetric measurement of hydrogen desorption from magnesium hydride powders using the model has been demonstrated. © 2015 Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

The 'shrinking core' model has been applied for the evaluation of hydrogen desorption kinetics during decomposition of magnesium hydride. According to our estimation, the full desorption time is expected to have a quadratic dependence on the size of powder particles, if the bulk diffusion of hydrogen atoms in magnesium is a rate controlling step. However, for the actual diffusion rate for hydrogen in magnesium bulk the diffusion cannot significantly influence the overall desorption kinetics for microand nano-powders. © The Royal Society of Chemistry 2015.

Amorphous hydrogenated carbon (a-C:H) deposited on steel with plasma enhanced chemical vapor deposition can be used as elongation tolerant oxygen barrier. However, the elongation tolerance of the a-C:H film is lost if deposited on a poly(ethylene terephthalate) (PET) for reasons unknown. To assess this phenomenon, a-C:H was deposited on PET, silicon substrates, and silicon micro-cantilevers, and the stress was determined by measuring the radius of curvature. a-C:H deposited on PET showed lower compressive stress than on silicon. This difference is not due to the formation of a gradient layer or plastic deformation of PET. Instead, the most probable explanation is that energetic ions cause a partial release of biaxial orientation within the PET, thereby reducing the compressive stress. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A miniaturized biofuel cell (BFC) is powering an electrolyser invoking a glucose concentration dependent formation of a dye which can be determined spectrophotometrically. This strategy enables instrument free analyte detection using the analyte-dependent BFC current for triggering an optical read-out system. A screen-printed electrode (SPE) was used for the immobilization of the enzymes glucose dehydrogenase (GDH) and bilirubin oxidase (BOD) for the biocatalytic oxidation of glucose and reduction of molecular oxygen, respectively. The miniaturized BFC was switched-on using small sample volumes (ca. 60μL) leading to an open-circuit voltage of 567mV and a maximal power density of (6.8±0.6) μWcm-2. The BFC power was proportional to the glucose concentration in a range from 0.1 to 1.0mM (R2=0.991). In order to verify the potential instrument-free analyte detection the BFC was directly connected to an electrochemical cell comprised of an optically-transparent SPE modified with methylene green (MG). The reduction of the electrochromic reporter compound invoked by the voltage and current flow applied by the BFC let to MG discoloration, thus allowing the detection of glucose. © 2015 Elsevier B.V..

We have examined the reactivity of water-covered Si(0 0 1)-2?×1, (H,OH)-Si(0 0 1)-2?×1, with propanoic (C2H5COOH) acid at room temperature. Using a combination of spectroscopic techniques probing the electronic structure (XPS, NEXAFS) and the vibrational spectrum (HREELS), we have proved that the acid is chemisorbed on the surface as a propanoate. Once the molecule is chemisorbed, the strong perturbation of the electronic structure of the hydroxyls, and of their vibrational spectrum, suggests that the molecule makes hydrogen bonds with the surrounding hydroxyls. As we find evidence that surface hydroxyls are involved in the adsorption reaction, we discuss how a concerted or a radical-mediated reaction (involving the surface silicon dangling bonds) could lead to water elimination and formation of the ester. © 2015 IOP Publishing Ltd.

A study of particle size effects during the catalytic CO2 electroreduction on size-controlled Cu nanoparticles (NPs) is presented. Cu NP catalysts in the 2-15 nm mean size range were prepared, and their catalytic activity and selectivity during CO2 electroreduction were analyzed and compared to a bulk Cu electrode. A dramatic increase in the catalytic activity and selectivity for H2 and CO was observed with decreasing Cu particle size, in particular, for NPs below 5 nm. Hydrocarbon (methane and ethylene) selectivity was increasingly suppressed for nanoscale Cu surfaces. The size dependence of the surface atomic coordination of model spherical Cu particles was used to rationalize the experimental results. Changes in the population of low-coordinated surface sites and their stronger chemisorption were linked to surging H2 and CO selectivities, higher catalytic activity, and smaller hydrocarbon selectivity. The presented activity-selectivity-size relations provide novel insights in the CO2 electroreduction reaction on nanoscale surfaces. Our smallest nanoparticles (∼2 nm) enter the ab initio computationally accessible size regime, and therefore, the results obtained lend themselves well to density functional theory (DFT) evaluation and reaction mechanism verification. © 2014 American Chemical Society.

Metal-free nitrogen modified carbon catalysts (NC) are very closely related to MNC catalysts which contain a transition metal(s) (M), usually Fe or Co as an essential constituent. We investigated the influence of metal inclusions on the activity of nitrogen-doped carbon black in the electrocatalysis of the oxygen reduction reaction (ORR). A reference metal-free NC catalyst was prepared by pyrolysis of a polypyrrole/Vulcan XC72 composite at 800 °C for 2 h under helium. Controlled amounts of Co, Fe, Mn and Ni in low concentrations were then introduced into NC by impregnating it with the corresponding meso-tetra(4-pyridyl) porphyrin metal complex followed by further pyrolysis at 650 °C for 2 h under helium. The resulting catalysts were investigated for ORR using rotating disk electrode and rotating-ring disk electrode voltammetry in 0.1 M KOH. Additionally, the rate of decomposition of hydrogen peroxide by the different catalysts was determined in order to probe the influence of the metal inclusions on the mechanism and selectivity of the ORR. The results show that Fe, Co and Mn inclusions cause a substantial decrease of the overpotential of the reaction and enhance the catalytic current, whereas the presence of Ni has a poisoning effect on ORR. In the presence of Fe, the catalysts apparently reduce oxygen selectively to OH- in a direct four electron transfer process as opposed to the two-step, two electron pathway involving hydrogen peroxide as an intermediate for the case of the NC catalyst. © 2013 Elsevier Ltd.

Nanoporous Cu-O system catalysts with different oxidation states of Cu have been fabricated through a combination of dealloying as-milled Al66.7Cu33.3 alloy powders and subsequent thermal annealing. X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) have been used to characterize the microstructure and surface chemical states of Cu-O catalysts. The peculiar nanoporous structure can be retained in Cu-O catalysts after thermal treatment. Catalytic experiments reveal that all the Cu-O samples exhibit complete CO conversion below 170 °C. The optimal catalytic performance could be achieved through the combination of annealing in air with hydrogen treatment for the Cu-O catalyst, which shows a near complete conversion temperature (T90%) of 132 °C and an activation energy of 91.3 KJ mol-1. In addition, the present strategy (ball milling, dealloying and subsequent thermal treatment) could be scaled up to fabricate high-performance Cu-O catalysts towards CO oxidation. This journal is © The Royal Society of Chemistry 2014.

Advanced solid-state 2D NMR spectroscopy and molecular dynamics computation are employed to investigate the interaction between adsorbed ferrocene molecules and the MOF-5 lattice. Relayed 13C-1H heteronuclear correlation (HETCOR) 2D NMR spectra clearly indicate short-distance contacts between the ferrocene guests and the benzene-1,4-dicarboxylic-acid linkers, mediated via intermolecular 1 H spin diffusion. By use of 2D 1H-1H correlation spectroscopy the distances between 1H nuclei in the guests and the linkers are estimated to be shorter than 0.5 nm. MD computer simulations support the interpretation of the 2D solid state NMR studies. Moreover, they suggest a wide distribution of intermolecular distances in this host-guest system with the shortest intermolecular hydrogen-hydrogen distances of 0.15 nm. © 2013 Elsevier Inc. All rights reserved.

This work focuses on the synthesis, characterization and testing of mixed protonic-electronic conducting membrane materials for H2 separation from gas mixtures capable of operating in a membrane reactor at temperatures higher than 600°C. La5.5WO12-δ and selected substituted barium zirconates with stoichiometries BaCe0.5Zr0.4Y0.1O3-δ and BaCe0.2Zr0.7Yb0.08Ni0.02O3-δ were therefore characterized and tested under coal-gasification-related conditions at 600-900°C. Sintered samples of the synthesized substituted barium zirconates were characterized by measuring the total conductivity and the thermal expansion coefficients. Also particle size distributions, BET surface-areas and elemental analysis of the starting powders, including commercial La5.5WO12-δ were specified. The compounds were exposed to syngas with steam, as well as to an atmosphere mainly consisting of CO2. The microstructure and phase composition of the membrane materials were studied by SEM, EDX and XRD before and after exposure. BaCe0.2Zr0.7Yb0.08Ni0.02O3-δ shows a very promising chemical stability from 600°C to 900°C and La5.5WO12-δ at 900°C. © 2014 Elsevier Ltd.

Fatigue experiments have been performed on superelastic NiTi double-notched plate form specimens with different notch types and sizes. The fatigue loading was controlled by the average stress at the minimum cross-section. The fatigue life as well as the fatigue fracture surface has been investigated in detail. The fatigue life decreases from specimens without notches, to specimens with semi-circular notches followed by v-type notched specimens. Specimens with crack notches show the shortest fatigue lives. The fatigue life decreases with increasing the notch acuity. Not only notch type but also notch size affects the fatigue life under the same macro-average stress. The fatigue fracture surfaces are quite similar to those of the conventional ductile materials with crack initiation, propagation and final fracture area. Typical characteristics of low cycle fatigue surfaces such as multi-fatigue crack initiation sites, weak striations and tyre-like patterns were found. Finite element (FE) simulations were performed to investigate the stress and phase transformation distributions in order to explain and understand the experimental results. © 2014 Elsevier B.V.

This paper presents a stacked sensor concept, which is producible entirely on standard printed circuit boards and applicable for the control of industrial plasma processes. Starting with the so-called multipole resonance probe (MRP) the prospects and the development towards the stacked MRP (sMRP) are discussed. The conversion of the MRP into a discretized spherical setup, using printed half discs of varying radii, is investigated. 3D electromagnetic field simulations yield an optimized assembly of 25 PCBs for a replication of the probe head. Measurements of a first prototype in a double inductive coupled plasma with an excited argon-hydrogen plasma have proven the expected resonance behaviour. In comparison to the MRP and the simulations, the applicability of the stacked sensor concept is demonstrated. © 2014 IEEE.

Electron-transfer pathways between cellobiose dehydrogenase from Myriococcum thermophilum (MtCDH) and the related flavodehydrogenase domain (FAD-MtCDH) and electrodes were evaluated using specifically designed Os-complex modified electrodeposition paints (EDPs). The properties of the Os-complex modified EDPs were varied by variation of the monomer composition, the coordination sphere of the polymer-bound Os-complexes, and the length and flexibility of the spacer chain between Os complex and polymer backbone. The MtCDH-to-EDP weight ratio, the pH value, as well as the operational temperature have been optimized. © 2013 Elsevier Ltd.

The electrocatalytic reduction of CO2 to industrial chemicals and fuels is a promising pathway to sustainable electrical energy storage and to an artificial carbon cycle, but it is currently hindered by the low energy efficiency and low activity displayed by traditional electrode materials. We report here the size-dependent catalytic activity of micelle-synthesized Au nanoparticles (NPs) in the size range of ∼1-8 nm for the electroreduction of CO2 to CO in 0.1 M KHCO3. A drastic increase in current density was observed with decreasing NP size, along with a decrease in Faradaic selectivity toward CO. Density functional theory calculations showed that these trends are related to the increase in the number of low-coordinated sites on small NPs, which favor the evolution of H2 over CO2 reduction to CO. We show here that the H2/CO product ratio can be specifically tailored for different industrial processes by tuning the size of the catalyst particles. © 2014 American Chemical Society.

CO2 hydrogenation to short-chain hydrocarbons was investigated over iron catalysts supported on oxygen- and nitrogen-functionalized multi-walled carbon nanotubes (CNTs) and on silica, which were synthesized by the dry impregnation method using ammonium ferric citrate as precursor. The reduction of the calcined catalysts was examined in detail using temperature-programmed reduction in H2 and in situ X-ray absorption near-edge structure (XANES) analysis. The XANES results revealed that the mixture of hematite and magnetite was gradually transformed into wustite and metallic iron during heating in H2. Iron oxide nanoparticles supported on nitrogen-functionalized CNTs were easier to reduce compared to those on oxygen-functionalized CNTs indicating a promoting effect of the nitrogen functional groups. The interaction between iron oxide and silica was found to be much stronger inhibiting the reduction to metallic iron. As a result, the catalytic activity of iron nanoparticles supported on CNTs in CO2 hydrogenation at 360 °C, 25 bar and a H2:CO 2 ratio of 3 was almost twofold higher compared with iron supported on silica. CO2 was converted into C1-C5 hydrocarbons with CO and methane as major products over all catalysts. The Fe/NCNT catalyst achieved the highest olefin selectivity of 11% in the hydrocarbons range of C2-C5. In contrast, mostly paraffins were formed over the Fe/SiO2 catalyst. © 2014 Elsevier B.V.

Plasma sterilization is a promising alternative to commonly used sterilization techniques, because the conventional methods suffer from certain limitations, e.g. incompatibility with heat-sensitive materials, or use of toxic agents. However, plasma-based sterilization mechanisms are not fully understood yet. A low-pressure very high frequency capacitively coupled plasma is used to investigate the impact of a hydrogen discharge on the protein glyceraldehyde 3-phosphate dehydrogenase (GapDH). GapDH is an enzyme of glycolysis. As a part of the central metabolism, it occurs in nearly all organisms from bacteria to humans. The plasma is investigated with absolutely calibrated optical emission spectroscopy in order to identify and to quantify plasma components that can contribute to enzyme inactivation. The contribution of UV photons and heat to GapDH inactivation is investigated separately, and neither seems to be a major factor. In order to investigate the mechanisms of GapDH inactivation by the hydrogen discharge, samples are investigated for etching, induction of amino acid backbone breaks, and chemical modifications. While neither etching nor strand breaks are observed, chemical modifications occur at different amino acid residues of GapDH. Deamidations of asparagines as well as methionine and cysteine oxidations are detected after VHF-CCP treatment. In particular, oxidation of the cysteine in the active centre is known to lead to GapDH inactivation. © 2014 IOP Publishing Ltd.

Graphite electrodes were modified with specifically designed Os-complex modified electrodeposition polymers exhibiting a formal potential of the polymer-bound complex of about 0 to 20 mV (vs. Ag/AgCl/3MKCl) which is only about 100 mV anodic of the formal potential of pyrroloquinoline quinone (PQQ) in PQQ-dependent glucose dehydrogenase (PQQ-GDH). The efficiency of wiring the polymer-entrapped PQQ-GDH was dependent on the nature of the polymer backbone, the crosslinking with bifunctional crosslinkers and the co-entrapment of multi-walled carbon nanotubes. Due to the limited long-term stability a new polymer synthesis strategy was adapted using the same Os-complex but providing enhanced crosslinking capabilities by introducing epoxide functions at the polymer backbone. Related bioelectrodes showed enhanced glucose-dependent current and a stability of at least 3 days of continuous operation. © The Author(s) 2014.

Metal-organic frameworks are promising materials for manifold applications. This Minireview highlights approaches for the fine-tuning of specific sorption properties (e.g. capacity, selectivity, and breathing behavior) of this interesting class of materials. Central aspects covered are the control over the crystal morphology, the targeted tuning of sorption properties by judicious choice of metal centers and linkers, and the preparation of host-guest systems. We want to introduce the reader to these topics on the basis of the manipulation of a handful of outstanding prototypical metal-organic frameworks. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The electron transfer kinetics associated with both the reduction of oxygen and of protons to form hydrogen at gold nanoparticles are shown to display strong retardation when studied at citrate capped ultra small (2 nm) gold nanoparticles. Negative nanocatalysis in the hydrogen evolution reaction (HER) is reported for the first time. This journal is © the Partner Organisations 2014.

A joint experimental and computational study on the glucose-fructose conversion in water is reported. The reactivity of different metal catalysts (CrCl3, AlCl3, CuCl2, FeCl3, and MgCl2) was analyzed. Experimentally, CrCl3 and AlCl3 achieved the best glucose conversion rates, CuCl2 and FeCl3 were only mediocre catalysts, and MgCl2 was inactive. To explain these differences in reactivity, DFT calculations were performed for various metal complexes. The computed mechanism consists of two proton transfers and a hydrogen-atom transfer; the latter was the rate-determining step for all catalysts. The computational results were consistent with the experimental findings and rationalized the observed differences in the behavior of the metal catalysts. To be an efficient catalyst, a metal complex should satisfy the following criteria: moderate Brønsted and Lewis acidity (pKa=4-6), coordination with either water or weaker σ donors, energetically low-lying unoccupied orbitals, compact transition-state structures, and the ability for complexation of glucose. Thus, the reactivity of the metal catalysts in water is governed by many factors, not just the Lewis acidity. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hydrogen embrittlement affects high-strength ferrite/martensite dual-phase (DP) steels. The associated micromechanisms which lead to failure have not been fully clarified yet. Here we present a quantitative micromechanical analysis of the microstructural damage phenomena in a model DP steel in the presence of hydrogen. A high-resolution scanning electron microscopy-based damage quantification technique has been employed to identify strain regimes where damage nucleation and damage growth take place, both with and without hydrogen precharging. The mechanisms corresponding to these regimes have been investigated by employing post-mortem electron channeling contrast imaging and electron backscatter diffraction analyses, as well as additional in situ deformation experiments. The results reveal that damage nucleation mechanism (i.e. martensite decohesion) and the damage growth mechanisms (e.g. interface decohesion) are both promoted by hydrogen, while the crack-arresting capability of the ferrite is significantly reduced. The observations are discussed on the basis of the hydrogen-enhanced decohesion and hydrogen-enhanced localized plasticity mechanisms. We discuss corresponding microstructure design strategies for better hydrogen-related damage tolerance of DP steels. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Different modification procedures to stabilize and control the orientation of Myrothecium verrucaria bilirubin oxidase (MvBOD) on 3D carbon nanotube/carbon microfiber-modified graphite electrode surfaces were evaluated for the development of biofuel-cell cathodes. The surface properties of different linkers for covalent binding of BOD were investigated by using atomic force microscopy-based techniques. For all immobilization strategies, the maximal current response was obtained at a pH value of 6.5 with temperatures between 20 and 35°C. The biocathode based on MvBOD immobilized through an imino bond to the electrode showed the highest current density (1600μAcm-2) and was resistant to the presence of chloride ions. A biofuel cell was constructed, and it exhibited a maximal power of 54μWcm-2 at 350mV with an open-circuit voltage of about 600mV by using a cellobiose dehydrogenase based bioanode and glucose as the fuel. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The increasing demand for energy and limited reserves of fossil resources as well as climate change will in the near future require the transition from fossil to renewable feedstocks for sustainable production of fuels. In the following text several well-established and also emerging technologies for hydrogen production and its integration into energy-rich carrier molecules, such as methane, methanol, oxygenates, and synthetic petroleum fuel are presented and discussed. Several important factors like the possibility of large-scale production, compatibility with existing distribution and storage infrastructure, efficient energy extraction on demand, and last but not least, tolerable impact on the environment will play key roles. Each of the fuels has its own characteristics, and thus there may not be one single solution, but the coexistence of different fuels, depending on regional boundary conditions. © 2015 Elsevier B.V. All rights reserved.

A microscopic understanding of the processes that lead to hydrogen embrittlement is of critical importance for developing new generations of high-strength steels. With this article, we provide an overview of insights that can be gained from ab initio based methods when investigating the segregation and diffusion mechanisms of hydrogen in steels. We first discuss the solubility and diffusion behavior of hydrogen in the ferrite, austenite, and martensite phases. We consider not only defect-free bulk phases but also the influence of alloying elements and geometric defects such as vacancies and grain boundaries. In the second part, the behavior of hydrogen in the presence of precipitates, the solubility, the surface absorption, and the influence of hydrogen on the interface cohesion are studied. Finally, we provide simulation results for the interaction of hydrogen with dislocations. For all these applications, we will comment on advantages and shortcomings of ab initio methods and will demonstrate how the obtained data and insights can complement experimental approaches to extract general trends and to identify causes of hydrogen embrittlement. © 2014 The Minerals, Metals & Materials Society.

The structural organization of water at a model of amorphous silica-liquid water interface is investigated by ab initio molecular dynamics (AIMD) simulations at room temperature. The amorphous surface is constructed with isolated, H-bonded vicinal and geminal silanols. In the absence of water, the silanols have orientations that depend on the local surface topology (i.e. presence of concave and convex zones). However, in the presence of liquid water, only the strong inter-silanol H-bonds are maintained, whereas the weaker ones are replaced by H-bonds formed with interfacial water molecules. All silanols are found to act as H-bond donors to water. The vicinal silanols are simultaneously found to be H-bond acceptors from water. The geminal pairs are also characterized by the formation of water H-bonded rings, which could provide special pathways for proton transfer(s) at the interface. The first water layer above the surface is overall rather disordered, with three main domains of orientations of the water molecules. We discuss the similarities and differences in the structural organization of the interfacial water layer at the surface of the amorphous silica and at the surface of the crystalline (0 0 0 1) quartz surface. © 2014 IOP Publishing Ltd.

A d-lactate-selective biosensor has been developed using cellsdebris of recombinant thermotolerant methylotrophic yeast Hansenula polymorpha, overproducing d-lactate: cytochrome c-oxidoreductase (EC 1.1.2.4, d-lactate dehydrogenase (cytochrome), DlDH). The H. polymorpha DlDH-producer was constructed in two steps. First, the gene CYB2 was deleted on the background of the C-105 (gcr1 catX) strain of H. polymorpha impaired in glucose repression and devoid of catalase activity to avoid specific l-lactate-cytochrome c oxidoreductase activity. Second, the homologous gene DLD1 coding for DlDH was overexpressed under the control of the strong H. polymorpha alcohol oxidase promoter in the frame of a plasmid for multicopy integration in the Δcyb2 strain. The selected recombinant strain possesses 6-fold increased DlDH activity as compared to the initial strain. The cellsdebris was used as a biorecognition element of a biosensor, since DlDH is strongly bound to mitochondrial membranes. The cellsdebris, prepared by mechanic disintegration of recombinant cells, was immobilized on a graphite working electrode in an electrochemically generated layer using an Os-complex modified cathodic electrodeposition polymer. Cytochrome c was used as additional native electron mediator to improve electron transfer from reduced DlDH to the working electrode. The constructed d-lactate-selective biosensors are characterized by a high sensitivity (46.3-61.6 A M-1 m-2), high selectivity and sufficient storage stability. © 2014 Elsevier B.V.

Hydrogenases are nature's efficient catalysts for both the generation of energy via oxidation of molecular hydrogen and the production of hydrogen via the reduction of protons. However, their O2 sensitivity and deactivation at high potential limit their applications in practical devices, such as fuel cells. Here, we show that the integration of an O2 -sensitive hydrogenase into a specifically designed viologen-based redox polymer protects the enzyme from O2 damage and high-potential deactivation. Electron transfer between the polymer-bound viologen moieties controls the potential applied to the active site of the hydrogenase and thus insulates the enzyme from excessive oxidative stress. Under catalytic turnover, electrons provided from the hydrogen oxidation reaction induce viologen-catalysed O 2 reduction at the polymer surface, thus providing self-activated protection from O2. The advantages of this tandem protection are demonstrated using a single-compartment biofuel cell based on an O2 -sensitive hydrogenase and H2/O2 mixed feed under anode-limiting conditions.

There are several strategies to improve the electrochemical performance of TiO2 as negative electrode material for Li-ion batteries. Introducing oxygen vacancies through hydrogen reduction leads to an enhancement in electrical conductivity. However, this strategy does not improve the low lithium-ion mobility. Herein, we show that by decreasing the temperature of hydrogen annealing the improved lithium-ion mobility of high-surface-area TiO2 and β-TiO2 can be combined with the enhanced electrical conductivity of oxygen deficiencies. Annealing at only 275–300 °C in pure hydrogen atmosphere successfully creates oxygen vacancies in TiO2, as confirmed by UV/Vis spectroscopy, whereas the temperature is low enough to maintain a high specific surface area and prevent β-to-anatase phase transformation. The hydrogen reduction of high-surface-area anatase or anatase/β-TiO2 at these temperatures leads to improvements in the performance, achieving charge capacities of 142 or 152 mAh g−1 at 10C, respectively. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper presents a thermogravimetric analysis of catalytic methane decomposition using ordered mesoporous carbon nanorods (CMK-3) and ordered mesoporous carbidederived carbon (DUT-19) as catalysts. X-ray diffraction and N2 physisorption analyses were performed for both fresh catalysts. Threshold temperatures for methane decomposition with DUT-19 and CMK-3 were estimated by three different methods found in literature. Carbon formation rate and carbon weight gain as a function of time at various temperatures and methane partial pressures were studied, and the kinetics of CMK-3 and DUT-19 as catalysts for methane decomposition were investigated. Arrhenius energy values of 187 kJ/mol for CMK-3 and 196 kJ/mol for DUT-19 with a reaction order of 0.5 were obtained for both catalysts. Results show that carbon deposition on the catalyst during the reaction lead to catalyst deactivation with significant surface modification. Scanning electron microscope studies of fresh and deactivated catalyst samples show the blocking of catalyst pores and the formation of agglomerates on the outer surface of the catalyst during the course of reaction. DUT-19 catalytically outperforms CMK-3 because of a lower threshold temperature, higher surface area, and higher pore volume. These results show that ordered mesoporous carbons are promising catalysts for methane decomposition. © 2013 Elsevier Ltd. All rights reserved.

The redox interaction between hydroxyl groups on oxide surfaces and metal atoms and clusters deposited thereon, according to which metals get oxidized and hydrogen released, is an effective route to tune both the morphological (particle size and shape) and electronic (oxidation state) properties of oxide-supported metals. While the oxidation state of the metals can straightforwardly be probed by X-ray based methods (e.g., XPS), hydrogen is much more difficult to capture, in particular in highly reactive systems where the redox interaction takes place directly during the nucleation of the metals at room temperature. In the present study, the interaction of Pd with a hydroxylated MgO(001) surface was studied using a combination of vibrational spectroscopy, electronic structure studies including Auger parameter analysis, and thermal desorption experiments. The results provide clear experimental evidence for the redox nature of the interaction by showing a direct correlation between metal oxidation and hydrogen evolution at slightly elevated temperature (390 K). Moreover, a second hydrogen evolution pathway opens up at 500 K, which involves hydroxyl groups on the MgO support and carbon monoxide adsorbed on the Pd particles (water-gas shift reaction). © 2014 American Chemical Society.

Many energy conversion materials show increased performance, if the materials are used in nanostructured form. However, this could be detrimental for stability of the materials, since during cycling the nanostructuring tends to be lost because of particle growth. This problem may be solved by encapsulation of the active material in different types of matrices or coatings, which beyond the stabilization may also provide additional functionality, such as conductivity or mechanical reinforcement. This Perspective covers the general features of encapsulation strategies, and desribes selected examples for different types of energy conversion materials. At the end, promising development lines will be discussed, together with the need for a more systematic study of the effects of encapsulation. © 2013 American Chemical Society.

The physical and mechanical properties of a σ5 (310) [001] symmetrical tilt grain boundary (STGB) in body centred cubic (bcc) Fe are investigated by means of ab initio calculations with respect to the effect of a varying number of C and H atoms at the grain boundary. The obtained results show that with increasing number of C atoms the grain boundary energy is lowered, and the segregation energy remains negative up to a full coverage of the grain boundary with C. Thus, in a bcc Fe-C system with a sufficient amount of interstitial C, the C segregated state should be considered as the ground state of this interface. Ab initio uni-axial tensile tests of the grain boundary reveal that the work of separation as well as the theoretical strength of the σ5 (310) [001] STGB increases significantly with increasing C content. The improved cohesion due to C is mainly a chemical effect, but the mechanical contribution is also cohesion enhancing. The presence of hydrogen changes the cohesion enhancing mechanical contribution of C to an embrittling contribution, and also reduces the beneficial chemical contribution to the cohesion. When hydrogen is present together with C at the grain boundary, the reduction in strength amounts to almost 20% for the co-segregated case and to more than 25% if C is completely replaced by H. Compared to the strength of the STGB in pure iron, however, the influence of H is negligible. Hence, H embrittlement can only be understood in the three component Fe-C-H system. © 2014 Elsevier B.V.

Hydrogen embrittlement of a precipitation-hardened Fe-26Mn-11Al-1.2C (wt.%) austenitic steel was examined by tensile testing under hydrogen charging and thermal desorption analysis. While the high strength of the alloy (>1 GPa) was not affected, hydrogen charging reduced the engineering tensile elongation from 44 to only 5%. Hydrogen-assisted cracking mechanisms were studied via the joint use of electron backscatter diffraction analysis and orientation-optimized electron channeling contrast imaging. The observed embrittlement was mainly due to two mechanisms, namely, grain boundary triple junction cracking and slip-localization-induced intergranular cracking along micro-voids formed on grain boundaries. Grain boundary triple junction cracking occurs preferentially, while the microscopically ductile slip-localization-induced intergranular cracking assists crack growth during plastic deformation resulting in macroscopic brittle fracture appearance. © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

This study presents the deactivation kinetics of methane decomposition for the activated carbons Fluka-05105 and Fluka-05120, ordered mesoporous carbon (CMK-3), and ordered mesoporous carbide-derived carbon (DUT-19). The experimental and thermodynamically predicted carbon deposition, the average and total hydrogen production, and the effect of flow rate on carbon formation rate of these catalysts were investigated. Results indicate that the experimental conditions chosen were within the reaction control regime. Catalytic activity was calculated via two different definitions present in literature: one in terms of carbon deposition rate and the other in terms of carbon mass deposited. Deactivation kinetics were obtained by fitting the experimental data by nonlinear regression analysis. Differences between the two methods in determining activity resulted in significant changes in the estimation of deactivation kinetics. The activity calculated based on the rate method results in the best fit of experimentally collected data. A deactivation order and methane concentration dependency of approximately 1.0 and 0.5 were determined for all the catalysts tested (Fluka-05105, Fluka-05120, CMK-3, and DUT-19). The activation energy of deactivation (Ed) was determined to be 192, 154, 166, and 181 kJ/mol for Fluka-05120, Fluka-05105, CMK-3, and DUT-19, respectively. DUT-19 was the best performing catalyst in terms of carbon formation rate, total carbon production, hydrogen production rate, average hydrogen production, and total hydrogen production. © 2013 American Chemical Society.

Nanostructured, porous metals are of great interest for material scientists since they combine high surface area, gas permeability, electrical conductivity, plasmonic behavior, and size-enhanced catalytic reactivity. Here we present the formation of multimetallic porous three-dimensional networks by a template-free self-assembly process. Nanochains are formed by the controlled coalescence of Au, Ag, Pt, and Pd nanoparticles in aqueous media, and their interconnection and interpenetration leads to the formation of a self-supporting network. The resulting noble-metal-gels are transformed into solid aerogels by the supercritical drying technique. Compared to previously reported results, the technique is facilitated by exclusion of additional destabilizers. Moreover, temperature control is demonstrated as a powerful tool, allowing acceleration of the gelation process as well as improvement of its reproducibility and applicability. Electron microscopy shows the nanostructuring of the network and its high porosity. XRD and EDX STEM are used to investigate the alloying behavior of the bimetallic aerogels and prove the control of the alloying state by temperature induced phase modifications. Furthermore, the resulting multimetallic aerogels show an extremely low relative density (<0.2%) and a very high surface area (>50 m2/g) compared to porous noble metals obtained by other approaches. Electrically conductive thin films as well as hybrid materials with organic polymers are depicted to underline the processability of the materials, which is a key factor regarding handling of the fragile structures and integration into device architectures. Owing to their exceptional and tunable properties, multimetallic aerogels are very promising materials for applications in heterogeneous catalysis and electrocatalysis, hydrogen storage, and sensor systems but also in surface enhanced Raman spectroscopy (SERS) and the preparation of transparent conductive substrates. © 2013 American Chemical Society.

The measurement of key molecules in individual cells with minimal disruption to the biological milieu is the next frontier in single-cell analyses. Nanoscale devices are ideal analytical tools because of their small size and their potential for high spatial and temporal resolution recordings. Here, we report the fabrication of disk-shaped carbon nanoelectrodes whose radius can be precisely tuned within the range 5-200 nm. The functionalization of the nanoelectrode with platinum allowed the monitoring of oxygen consumption outside and inside a brain slice. Furthermore, we show that nanoelectrodes of this type can be used to impale individual cells to perform electrochemical measurements within the cell with minimal disruption to cell function. These nanoelectrodes can be fabricated combined with scanning ion conductance microscopy probes, which should allow high resolution electrochemical mapping of species on or in living cells. © 2013 American Chemical Society.

For practical solid-state hydrogen storage, reversibility under mild conditions is crucial. Complex metal hydrides such as NaAlH4 and LiBH4 have attractive hydrogen contents. However, hydrogen release and especially uptake after desorption are sluggish and require high temperatures and pressures. Kinetics can be greatly enhanced by nanostructuring, for instance by confining metal hydrides in a porous carbon scaffold. We present for a detailed study of the impact of the nature of the carbon-metal hydride interface on the hydrogen storage properties. Nanostructures were prepared by melt infiltration of either NaAlH4 or LiBH4 into a carbon scaffold, of which the surface had been modified, varying from H-terminated to oxidized (up to 4.4 O/nm2). It has been suggested that the chemical and electronic properties of the carbon/metal hydride interface can have a large influence on hydrogen storage properties. However, no significant impact on the first H2 release temperatures was found. In contrast, the surface properties of the carbon played a major role in determining the reversible hydrogen storage capacity. Only a part of the oxygen-containing groups reacted with hydrides during melt infiltration, but further reaction during cycling led to significant losses, with reversible hydrogen storage capacity loss up to 40% for surface oxidized carbon. However, if the carbon surface had been hydrogen terminated, ∼6 wt% with respect to the NaAlH4 weight was released in the second cycle, corresponding to 95% reversibility. This clearly shows that control over the nature and amount of surface groups offers a strategy to achieve fully reversible hydrogen storage in complex metal hydride-carbon nanocomposites. © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Prussian Blue (PB) deposited on a nanoelectrode is the basis for an amperometric hydrogen peroxide sensor. Carbon nanoelectrodes, fabricated from pyrolytic decomposition of butane within a quartz nanopipette, were electrochemically etched and PB was deposited in the formed nanocavity. This procedure significantly increased the stability of PB films while maintaining a high mean sensitivity of 50 A mol- 1 l cm- 2 for H 2O2 detection at - 50 mV vs. Ag/AgCl (0.1 M Cl -) at neutral pH value. Hydrogen peroxide was selectively quantified in the concentration range from 10 μM to 3 mM. We envision the application of these nanosensors to the intracellular monitoring of oxidative stress in living cells. © 2013 Elsevier B.V.

Hydrogen interstitials in austenitic Fe-Mn alloys were studied using density-functional theory to gain insights into the mechanisms of hydrogen embrittlement in high-strength Mn steels. The investigations reveal that H atoms at octahedral interstitial sites prefer a local environment containing Mn atoms rather than Fe atoms. This phenomenon is closely examined combining total energy calculations and crystal orbital Hamilton population analysis. Contributions from various electronic phenomena such as elastic, chemical, and magnetic effects are characterized. The primary reason for the environmental preference is a volumetric effect, which causes a linear dependence on the number of nearest-neighbour Mn atoms. A secondary electronic/magnetic effect explains the deviations from this linearity. © 2014 Wiley Periodicals, Inc.

A well-defined iron complex (3) supported by a bis(phosphino)amine pincer ligand efficiently catalyzes both acceptorless dehydrogenation and hydrogenation of N-heterocycles. The products from these reactions are isolated in good yields. Complex 3, the active catalytic species in the dehydrogenation reaction, is independently synthesized and characterized, and its structure is confirmed by X-ray crystallography. A trans-dihydride intermediate (4) is proposed to be involved in the hydrogenation reaction, and its existence is verified by NMR and trapping experiments. © 2014 American Chemical Society.

A mixed-linker solid-solution approach was employed to modify the metal sites and introduce structural defects into the mixed-valence Ru II/III structural analogue of the well-known MOF family [M 3 II,II(btc)2] (M=Cu, Mo, Cr, Ni, Zn; btc=benzene-1,3,5-tricarboxylate), with partly missing carboxylate ligators at the Ru2 paddle-wheels. Incorporation of pyridine-3,5-dicarboxylate (pydc), which is the same size as btc but carries lower charge, as a second, defective linker has led to the mixed-linker isoreticular derivatives of Ru-MOF, which display characteristics unlike those of the defect-free framework. Along with the creation of additional coordinatively unsaturated sites, the incorporation of pydc induces the partial reduction of ruthenium. Accordingly, the modified Ru sites are responsible for the activity of the "defective" variants in the dissociative chemisorption of CO 2, the enhanced performance in CO sorption, the formation of hydride species, and the catalytic hydrogenation of olefins. The defect engineering in Ru-based metal-organic frameworks (MOFs) at coordinatively unsaturated metal centers (CUS) induces partial reduction of the metal nodes and leads to properties that are absent for the parent MOF, such as dissociative chemisorption of CO2 and enhanced sorption capacity of CO. The modified MOFs offer new perspectives as multifunctional materials whose performance is controlled by design of the defects. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Understanding the interaction of hydrogen with subnanometer platinum nanoparticles (NPs) under industrially relevant conditions is of great importance to heterogeneous catalysis. In this work, we investigate the pressure-dependent changes in hydrogen coverage on size- and shape-selected Pt/γ-Al2O3 NPs by in situ X-ray absorption near-edge structure (XANES) analysis. Difference XANES calculations revealed an increase in the H/Pt ratio from 1.9 to 2.5 upon increasing the hydrogen pressure from 1 to 21 bar at room temperature (1 bar=100 kPa). In addition, extended X-ray absorption fine structure measurements of the local geometrical structure showed changes in Pt - Pt bond length and coordination number, revealing a morphological transformation in the NPs from a 2 D to a 3 D shape under increasing H2 pressure at room temperature. Such shape evolution leads to a decrease in the NP-support contact area and is thus expected to affect the NP stability against coarsening. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We present recent developments in the field of austenitic steels with up to 18% reduced mass density. The alloys are based on the Fe-Mn-Al-C system. Here, two steel types are addressed. The first one is a class of low-density twinning-induced plasticity or single phase austenitic TWIP (SIMPLEX) steels with 25–30 wt.% Mn and <4–5 wt.% Al or even <8 wt.% Al when naturally aged. The second one is a class of κ-carbide strengthened austenitic steels with even higher Al content. Here, κ-carbides form either at 500–600°C or even during quenching for >10 wt.% Al. Three topics are addressed in more detail, namely, the combinatorial bulk high-throughput design of a wide range of corresponding alloy variants, the development of microstructure–property relations for such steels, and their susceptibility to hydrogen embrittlement. © 2014, The Minerals, Metals & Materials Society.

Five different hydrous layer silicates (HLSs) containing fer layers (ferrierite-type layers) were obtained by hydrothermal syntheses from mixtures of silicic acid, water and tetraalkylammonium/tetraalkylphosphonium hydroxides. The organic cations had been added as structure directing agents (SDA). A characteristic feature of the structures is the presence of strong to medium strong hydrogen bonds between the terminal silanol/siloxy groups of neighbouring layers. The five-layered silicates differ chemically only with respect to the organic cations. Structurally, they differ with respect to the arrangement of the fer layers relative to each other, which is distinct for every SDA-fer-layer system. RUB-20 (containing tetramethylammonium) and RUB-40 (tetramethylphosphonium) are monoclinic with stacking sequence AAA and shift vectors between successive layers 1a0 + 0b0 + 0.19c 0 and 1a0 + 0b0 + 0.24c0, respectively. RUB-36 (diethyldimethylammonium), RUB-38 (methyltriethylammonium) and RUB-48 (trimethylisopropylammonium) are orthorhombic with stacking sequence ABAB and shift vectors 0.5a0 + 0b0 ± 0.36c 0, 0.5a0 + 0b0 + 0.5c0 and 0.5a 0 + 0b0 ± 0.39c0, respectively. Unprecedented among the HLSs, two monoclinic materials are made up of fer layers which possess a significant amount of ordered defects within the layer. The ordered defects involve one particular Si-O-Si bridge which is, to a fraction of ca. 50%, hydrolyzed to form nests of two Si-OH groups. When heated to 500-600 °C in air, the HLSs condense to form framework silicates. Although all layered precursors were moderately to well ordered, the resulting framework structures were of quite different crystallinity. The orthorhombic materials RUB-36, -38 and -48, general formula SDA4Si36O 72(OH)4, which possess very strong hydrogen bonds (d[O⋯O] ≈ 2.4 Å), transform into a fairly or well ordered CDO-type silica zeolite RUB-37. The monoclinic materials RUB-20 and -40, general formula SDA2Si18O36(OH)2OH, possessing medium strong hydrogen bonds (d[O⋯O] ≈ 2.65 Å) are transformed into poorly ordered framework silicates. Some rules of thumb can be established concerning the successful zeolite synthesis via a topotactic condensation of layered precursors. Favourably, the precursor (i) possesses already a well ordered structure without defects, (ii) contains strong inter-layer hydrogen bonds and does not contain strong intra-layer hydrogen bonds and (iii) contains a suitable cation. The nature of the organic cation (size, geometry, flexibility, thermal stability) plays a key role in the formation of a microporous tectosilicate with well ordered structure. RUB-36 which meets these criteria yields a well ordered condensation product (RUB-37). This journal is © the Partner Organisations 2014.

Determination of the exact structure of individual molecules is the ultimate goal of high-resolution microscopy. However, the resolution of scanning tunneling microscopy (STM) is intrinsically limited to the extent of molecular orbitals, which frequently do not differ for small changes in the molecular conformation. Here we use the position of water molecules during the first hydration steps of an azobenzene derivative on Au(111) to determine not only the orientation of the end groups with respect to the phenyl rings but also the orientation of the two phenyl rings with respect to the azo group. We investigate the co-adsorption of 4,4'-hydroxy-azobenzene and water molecules on Au(111) by low-temperature STM. The water molecules are attached exclusively to the hydroxyl end groups of the azobenzene derivatives. Predominantly the trans-azobenzene molecule with the two hydroxyl groups pointing into opposite directions is adsorbed. As corroborated by the attachment of a single water molecule to 4-anilino-4?-nitro azobenzene on the same inert surface, the method is generally applicable for structure determination of molecules with appropriate end groups. Our study thus gives unprecedented information about the intramolecular orientation based on the first real space observation of the hydration of a functional molecule. © 2014 American Chemical Society.

Hydrogenation of CO2 to hydrocarbons over iron nanoparticles supported on oxygen-functionalized multi-walled carbon nanotubes was studied in a fixed-bed U-tube reactor at 25 bar with a H2:CO2 ratio of 3. Conversion of CO2 was approximately 35% yielding C 1-C5 products at 360°C with methane and CO as major products. The CO2 equilibrium conversion for temperatures in the range of 320° to 420°C was analysed by using CHEMCAD simulation software. Comparison between experimental and simulated degrees of CO 2 conversion shows that reverse water gas shift equilibrium had been achieved in the investigated temperature range and that less than 47% of CO 2 can be converted to CO at 420°C. © 2014 Indian Academy of Sciences.

Compartmentalization is a major prerequisite for the origin of life on earth according to Wächtershäuser "Iron-Sulfur-World". The hypothesis is mainly based on an autocatalytic inorganic energy reproducing redox system consisting of iron and sulfur as requirement for the subsequent synthesis of complex organic structures. Here, we modified [FeFe]-hydrogenase models by means of covalent coupling to either oleic acid or the amphiphilic block copolymer polybutadiene-polyethyleneoxide (PB-PEO) and incorporated those into the membranes of vesicles composed of phospholipids (liposomes) or the unmodified amphiphilic polymer (polymersomes). We employed a [2Fe-2S] cluster as a hydrogenase model, since these structures are known to be suitable catalysts for the generation of H2 in the presence of weak acids. Successful incorporation was confirmed by spectrophotometric iron quantification and the vesicles formed were characterized by size determination (photon correlation spectroscopy (PCS)), and zeta potential as well as by cryo-transmission electron microscopy (Cryo-TEM). The modified models could be incorporated into liposomes or polymersomes up to molar proportions of 3.15% and 28%, respectively. Due to the immobilization in vesicular bilayers the [FeFe]-hydrogenase models can even exhibit catalytic action under the particular conditions of the intravesicular microenvironment. Our results suggest that the vesicular systems described may be applied as a nanoreactor for the reduction of encapsulated substances by generating hydrogen and thus as a minimal cell model. © 2014 Informa Healthcare USA, Inc.

The type and the amount of functional groups on the surface of carbon nanotubes (CNTs) were tuned to improve the activity of supported Co nanoparticles in hydrogenation catalysis. Surface nitrogen species on CNTs significantly promoted the decomposition of the cobalt precursor and the reduction of cobalt oxide, and improved the resistance of metallic Co against oxidation in ambient atmosphere. In the selective hydrogenation of nitrobenzene in the gas phase, Co supported on CNTs with the highest surface nitrogen content showed the highest activity, which is ascribed to the higher reducibility and the lower oxidation state of the Co nanoparticles under reaction conditions. For Co nanoparticles supported on CNTs with a smaller amount of surface nitrogen groups, a repeated reduction at 350 °C was essential to achieve a comparable high catalytic activity reaching 90% conversion at 250 °C, pointing to the importance of nitrogen species for the supported Co nanoparticles in nitrobenzene hydrogenation. © 2014 American Chemical Society.

Despite strong similarities due to the common presence of silicon monohydrides and isolated silicon dangling bonds (silicon radicals), the water-saturated Si(001)-2 × 1 surface and the hydrogen-terminated Si(001)-2 × 1 surface show very different reactivities with respect to benzaldehyde. By using real-time scanning tunneling microscopy, synchrotron radiation photoemission, X-ray absorption, and high-resolution electron energy loss spectroscopies in combination, we demonstrated that benzaldehyde reacts with the silicon dangling bonds of water-saturated Si (001). As we found no evidence for the abstraction of a nearby H leading to the formation of a new dangling bond, the formation of a stable radical adduct is a plausible explanation. This observation contrasts with the H-terminated case for which benzaldehyde grafting occurs via a radical chain reaction that can propagate after abstraction of a nearby H by the radical adduct. Also at odds with the H-terminated case, a second chemisorption channel is observed [i.e., a concerted hydrosilylation reaction between a surface monohydride (SiH) and the carbonyl moiety] without any participation of the silicon dangling bond. We discuss how the presence of hydroxyls on water-saturated Si(001)-2 × 1 could make its reactivity markedly different from that of H-terminated Si(001)-2 × 1. © 2014 American Chemical Society.

This chapter focuses on models for the mixed-valent Hox state as well as protonation reactions of Hred models and on some significant insights into proton reduction chemistry. Although numerous [FeFe] hydrogenase model complexes exist, synthetic access to iron-chalcogenolato compounds is limited to substitution reactions and oxidative additions. During the past two decades, significant development in modeling the active site of [FeFe] hydrogenases allowed to reveal the fundamental modes of action at the molecular level. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. All rights reserved.

Many well-established classical biomolecular force fields, fitted on the solvation properties of single ions, do not necessarily describe all the details of ion pairing accurately, especially for complex polyatomic ions. Depending on the target application, it might not be sufficient to reproduce the thermodynamics of ion pairing, but it may also be necessary to correctly capture structural details, such as the coordination mode. In this work, we analyzed how classical force fields can be optimized to yield a realistic description of these different aspects of ion pairing. Given the prominent role of the interactions of negatively charged amino-acid side chains and divalent cations in many biomolecular systems, we chose calcium acetate as a benchmark system to devise a general optimization strategy that we applied to two popular force fields, namely, GROMOS and OPLS-AA. Using experimental association constants and first-principles molecular dynamics simulations as a reference, we found that small modifications of the van der Waals ion-ion interaction parameters allow a systematic improvement of the essential thermodynamic and structural properties of ion pairing. © 2014 American Chemical Society.

We investigate an electrolytic route for hydrogen charging of metals and its detection in Atom Probe Tomography (APT) experiments. We charge an austenitic Fe-30Mn-8Al-1.2C (wt.%) weight reduced high-Mn steel and subsequently demonstrate the detectability of deuterium in an APT experiment. The experiment is repeated with a deposited Ag film upon an APT tip of a high-Mn steel. It is shown that a detectable deuterium signal can be seen in the high-Mn steel, and a D:H ratio of 0.84 can be reached in Ag films. Additionally, it was found that the predicted time constraint on detectability of D in APT was found to be lower than predicted by bulk diffusion for the high-Mn steel. Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Sputter deposition of Ir/IrOx on p+-n-Si without interfacial corrosion protection layers yielded photoanodes capable of efficient water oxidation (OER) in acidic media (1 M H2SO4). Stability of at least 18 h was shown by chronoamperomety at 1.23 V versus RHE (reversible hydrogen electrode) under 38.6 mW/cm2 simulated sunlight irradiation (λ > 635 nm, AM 1.5G) and measurements with quartz crystal microbalances. Films exceeding a thickness of 4 nm were shown to be highly active though metastable due to an amorphous character. By contrast, 2 nm IrOx films were stable, enabling OER at a current density of 1 mA/cm2 at 1.05 V vs. RHE. Further improvement by heat treatment resulted in a cathodic shift of 40 mV and enabled a current density of 10 mA/cm2 (requirements for a 10% efficient tandem device) at 1.12 V vs. RHS under irradiation. Thus, the simple IrOx/Ir/p+-n-Si structures not only provide the necessary overpotential for OER at realistic device current, but also harvest ∼100 mV of free energy (voltage) which makes them among the best-performing Si-based photoanodes in low-pH media. © 2014 American Chemical Society.

Sputter deposition of 50 nm thick NiO films on p+-n-Si and subsequent treatment in an Fe-containing electrolyte yielded highly transparent photoanodes capable of water oxidation (OER) in alkaline media (1 M KOH) with high efficiency and stability. The Fe treatment of NiO thin films enabled Si-based photoanode assemblies to obtain a current density of 10 mA/cm2 (requirement for >10% efficient devices) at 1.15 V versus RHE (reversible hydrogen electrode) under red-light (38.6 mW/cm2) irradiation. Thus, the photoanodes were harvesting ∼80 mV of free energy (voltage), which places them among the best-performing Si-based photoanodes in alkaline media. The stability was proven by chronoamperometry at 1.3 V versus RHE for 300 h. Furthermore, measurements with electrochemical quartz crystal microbalances coupled with ICP-MS showed minor corrosion under dark operation. Extrapolation of the corrosion rate showed stability for more than 2000 days of continuous operation. Therefore, protection by Fe-treated NiO films is a promising strategy to achieve highly efficient and stable photoanodes. © 2014 American Chemical Society.

A biofuel cell consisting of a self-powered sulfonamide immunosensor as biocathode and a cellobiose dehydrogenase (CDH)-based bioanode was developed for the determination of sulfonamide antibiotics in milk. A graphite-rod electrode was modified with proteinG for the immobilization of selective capture antibodies. A direct competitive immunoassay with a horseradish-peroxidase-labeled analog of the antibiotic and the 2,2′-azino-bis(3-ethyl benzothiazoline-6-sulfonic acid) diammonium salt-mediated reduction of H2O2 allows quantification of antibiotic residues. CDH was co-immobilized with a toluidine-blue-modified redox polymer on a graphite electrode for the biocatalytic oxidation of lactose in milk. An open-circuit voltage of 676mV and a maximal power density of 6.9μWcm-2 were obtained. The power densities measured at 550mV (vs. the anode) as a function of antibiotic concentration in milk samples allowed the construction of a calibration curve with a detection limit for sulfapyridine as low as 2.4ngmL-1. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hydrogenation of esters is vital to the chemical industry for the production of alcohols, especially fatty alcohols that find broad applications in consumer products. Current technologies for ester hydrogenation rely on either heterogeneous catalysts operating under extreme temperatures and pressures or homogeneous catalysts containing precious metals such as ruthenium and osmium. Here, we report the hydrogenation of esters under relatively mild conditions by employing an iron-based catalyst bearing a PNP-pincer ligand. This catalytic system is also effective for the conversion of coconut oil derived fatty acid methyl esters to detergent alcohols without adding any solvent. © 2014 American Chemical Society.

Protein immobilization on solid surfaces has become a powerful tool for the investigation of protein function. Physiologically relevant molecular reaction mechanisms and interactions of proteins can be revealed with excellent signal-to-noise ratio by vibrational spectroscopy (ATR-FTIR) on germanium crystals. Protein immobilization by thiol chemistry is well-established on gold surfaces, for example, for surface plasmon resonance. Here, we combine features of both approaches: a germanium surface functionalized with different thiols to allow specific immobilization of various histidine-tagged proteins with over 99% specific binding. In addition to FTIR, the surfaces were characterized by XPS and fluorescence microscopy. Secondary-structure analysis and stimulus-induced difference spectroscopy confirmed protein activity at the atomic level, for example, physiological cation channel formation of Channelrhodopsin 2. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Modification of the surface chemistry and correlated adhesive properties of polypropylene (PP) by means of an electron cyclotron resonance (ECR) oxygen plasma source is studied based on an in situ ultra-high-vacuum (UHV)-analytical approach. To determine the plasma induced chemical changes without exposure to atmosphere, X-ray excited valence band (VB) spectroscopy and core level X-ray photoelectron spectroscopy (XPS) are performed. Adhesive properties are characterized by means of UHV chemical force microscopy (UHV-CFM). Correlation of XPS and UHV-CFM data indicate that interactions between a SiO2-tip and the modified PP surface is dominated by hydrogen bonds between surface silanol groups on the tip and induced oxidized species on PP surface. Such interactions are maximized in the initial phase of surface oxidation.

The synthesis of 2,5-dimethylfuran (DMF) from 5-hydroxymethylfurfural (HMF) is a highly attractive route to a renewable fuel. However, achieving high yields in this reaction is a substantial challenge. Here it is described how PtCo bimetallic nanoparticles with diameters of 3.6 ± 0.7 nm can solve this problem. Over PtCo catalysts the conversion of HMF was 100% within 10 min and the yield to DMF reached 98% after 2 h, which substantially exceeds the best results reported in the literature. Moreover, the synthetic method can be generalized to other bimetallic nanoparticles encapsulated in hollow carbon spheres. © 2014 Macmillan Publishers Limited.

The fatigue properties of a novel high aluminum austenitic stainless steel with a high resistance against hydrogen embrittlement were investigated. S-N tests in 40 MPa H2 at -50 C resulted in a reduction in fatigue life by a factor of about 2 compared to air. Striation analysis revealed no acceleration of crack growth rate but accelerated crack initiation or accelerated short crack growth in H2. No apparent difference in fatigue fracture characteristics and striation morphology between the air and H2 tested specimens could be identified. Copyright © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Single-pulse femtosecond laser patterning of nitrobiphenylthiol monolayers on Au-coated Si substrates at λ = 800 nm, τ < 30 fs and ambient conditions has been investigated. After laser processing wet etching experiments are performed. Laser irradiation reduces the chemical resistance of the coating. In particular, the monolayer acts as a positive-tone resist. Burr-free pattern transfer is feasible at laser pulse fluences between 1 and 2.7 J/cm 2. Minimum structure sizes at a 1/e laser spot diameter of about 1 μm are close to 300 nm, i.e. sub-wavelength processing is demonstrated. Noteworthy, however, no indications for negative-tone resist properties of processed monolayers are evident, that is, cross-linking of the biphenyl moieties, if at all, is marginal. Also, complementary labeling experiments provide no evidence for chemical transformation of the nitro end groups into amine functionalities. Perspectives of resonant fs-laser processing in exploiting the particular prospects of nitrobiphenylthiol monolayers as negative-tone resists and chemically patternable platforms are discussed. © 2013 Elsevier B.V.

Improvements in current density and coulombic efficiency of a glucose oxidizing electrode were realized by a combination of pyranose dehydrogenase from Agaricus meleagris (AmPDH) with glucose dehydrogenase from Glomerella cingulata (GcGDH). The mixed enzyme electrode oxidizes glucose in several combinations at the C-1, C-2 and C-3 positions of the pyranose ring. This concerted action of enzymes increases (i) the coulombic efficiency by extracting more than 2e- per substrate molecule and (ii) the current density of the electrode when the mass-transfer of substrates becomes rate limiting. The electrodes were investigated with flow injection analysis (FIA) using different substrates under physiological conditions (pH 7.4). These investigations showed that the product of one enzyme can be used as substrate for the other enzyme and maximally 6e- can be gained from the oxidation of one glucose molecule using mixed enzyme electrode AmPDH/GcGDH/Os-polymer. We propose a bioanode for use in biofuel cells with an increased current density and coulombic efficiency obtained by a cascade reaction catalyzed by redox enzymes with a different site-specificity for glucose. © The Electrochemical Society.

A novel [FeFe]-hydrogenase model complex containing phosphine oxide in the dithiolato ligand, namely [Fe2(CO)6][(μ-SCH 2)2(Ph)Pi=O] (1), has been synthesized and characterized. Complex 1 was prepared via the reaction of equimolar quantities of (μ-LiS)2Fe2(CO)6 and Oi=P(Ph)(CH 2Cl)2. The protonation properties of complex 1 have been investigated by monitoring the changes in IR (in the ν(CO) region) and 31P{1H} NMR spectra upon addition of pyridinium tetrafluoroborate, [HPy][BF4], and BF4·Et 2O, suggesting protonation of the Pi=O functionality. In addition, high-level DFT calculations on the protonation sites of complex 1 in CH 2Cl2 have been performed and support our experimental observations that the Pi=O unit is protonated by HBF4·Et 2O. Cyclic voltammetric experiments on complex 1 showed an anodic shift of the oxidation peak upon addition of HBF4·Et 2O, suggesting a CE process. © 2013 American Chemical Society.

The surface oxide layer on nine different types of solution-annealed austenitic stainless steel (ASS) was evaluated by Secondary Ion Mass Spectrometry (SIMS). Tensile tests were conducted at 25 C and -50 C in hydrogen at 40 MPa and in air at atmospheric pressure. Relative reduction of area (RRA) was calculated accordingly. Additionally the martensite transformation curves were measured in air at -50 C to evaluate the probability of the formation of α′ martensite nuclei. A linear relationship between RRA and the calculated probability of the nucleation of α′ martensite nuclei was found on samples represented by the following three oxides types; (a) thick oxide, (b) decaying sub-surface oxide and (c) thin surface oxides. However, type (d) with high constant oxide level down to 60 nm depth does not follow the trend. The observed variation of the oxide layer is linked to the variability of tensile test results. © 2013 Published by Elsevier B.V.

Layered RUB-36 and PREFER (lamellar precursor of ferrierite) are the precursors of CDO and FER-type zeolites, respectively. Both are composed of the same ferrierite (FER) layer building blocks. Topotactic conversion from RUB-36 to pure silica zeolite ZSM-35 has been demonstrated in the presence of a surfactant cetyltrimethylammonium hydroxide (CTAOH). The transformation mechanism of this process was revealed, for the first time, by the detailed investigations of powder X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal analysis, and one-and two-dimensional (2-D) solid-state magic-angle spinning nuclear magnetic resonance (MAS NMR) as well as theoretical simulations. During swelling at room temperature, cetyltrimethylammonium cations (CTA+) replacing the original template were intercalated into FER layers to expand the interlayer distance remarkably and consequently to destroy the strong hydrogen-bonding interactions between the layers. 2-D 1H-29Si heteronuclear correlation (HETCOR) NMR indicates that the surfactant polar heads approximate the FER layers in swollen RUB-36. After deswelling, only a small amount of CTA+ cations with long tails lay in the void space between the FER layers. The Monte Carlo simulations on the deswollen RUB-36 further elucidate the occlusion of CTA+ cations in the pre-10 member ring of the layered ferrierite precursor, which may act as the structure-directing agent for the formation of FER-structured zeolite. The FER layer reassembly from the alteration of CTA+ conformation at the interlayers is of key importance to the topotactic transformation of RUB-36 to FER-type zeolite by the dehydration-condensation reaction. This may open up more applications in the lamellar zeolite system by the layer restacking approach. © 2013 American Chemical Society.

A bioanode with high current density and coulombic efficiency was developed by co-immobilization of pyranose dehydrogenase from Agaricus meleagris (AmPDH) with the dehydrogenase domain of cellobiose dehydrogenase from Corynascus thermophiles (recDH. CtCDH) expressed recombinantly in Escherichia coli. The two enzymes were entrapped in Os-complex modified electrodeposition polymers (Os-EDPs) with specifically adapted redox potential by means of chemical co-deposition. AmPDH oxidizes glucose at both the C2 and C3 positions whereas recDH. CtCDH oxidizes glucose only at the C1 position. Electrochemical measurements reveal that maximally 6 electrons can be harvested from one glucose molecule at the two-enzyme anode via a cascade reaction, as AmPDH oxidizes the products formed from of the recDH. CtCDH catalyzed substrate oxidation and vice versa. Furthermore, a significant increase in current density can be obtained by combining AmPDH and recDH. CtCDH in a single modified electrode. We propose the use of this bioanode in biofuel cells with increased current density and coulombic efficiency. © 2012 Elsevier B.V.

The utilization of light and inexpensive catalysts to afford hydrogen represents a huge challenge. Following our interest in silicon-containing [FeFe]-hydrogenase ([FeFe]-H2ase) mimics, we report a new model approach for a photocatalytic [FeFe]-H2ase mimic 1, which contains a 1-silafluorene unit as a photosensitizer. Thereby, the photoactive ligand is linked to the [2Fe2S] cluster through S-CH2-Si bridges. Photochemical H2 evolution experiments were performed and revealed a turnover number (TON) of 29. This is the highest reported photocatalytic efficiency for an [FeFe]-H2ase model complex in which the photosensitizer is covalently linked to the catalytic center. We report a viable synthetic pathway for the construction of a new photoactive model of the [FeFe]-hydrogenase ([FeFe]-H2ase) active site with a dithiolate bridge and 1-silafluorene as a photosensitizer. The [FeFe]-H2ase mimic represents a very compact, easily accessible, and inexpensive photocatalyst for hydrogen generation. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

After initial testing and optimization of anode biocatalysts, a membraneless glucose/oxygen enzymatic biofuel cell possessing high coulombic efficiency and power output was fabricated and characterized. Two sugar oxidizing enzymes, namely, pyranose dehydrogenase from Agaricus meleagris (AmPDH) and flavodehydrogenase domains of various cellobiose dehydrogenases (DHCDH) were tested during the pre-screening. The enzymes were mixed, "wired" and entrapped in a low-potential Os-complex-modified redox-polymer hydrogel immobilized on graphite. This anode was used in combination with a cathode based on bilirubin oxidase from Myrothecium verrucaria adsorbed on graphite. Optimization showed that the current density for the mixed enzyme electrode could be further improved by using a genetically engineered variant of the non-glycosylated flavodehydrogenase domain of cellobiose dehydrogenase from Corynascus thermophilus expressed in E. coli (ngDHCtCDHC310Y) with a high glucose-turnover rate in combination with an Os-complex-modified redox polymer with a high concentration of Os complexes as well as a low-density graphite electrode. The optimized biofuel cell with the AmPDH/ngDHCtCDHC310Y anode showed not only a similar maximum voltage as with the biofuel cell based only on the ngDH CtCDHC310Y anode (0.55 V) but also a substantially improved maximum power output (20 μW cm-2) at 300 mV cell voltage in air-saturated physiological buffer. Most importantly, the estimated half-life of the mixed biofuel cell can reach up to 12 h, which is apparently longer than that of a biofuel cell in which the bioanode is based on only one single enzyme. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Gold nanoparticles have been efficiently photodeposited onto titanate-loaded SBA-15 (Ti(x)/SBA-15) with different titania coordination. Transmission electron microscopy shows that relatively large Au nanoparticles are photodeposited on the outer surface of the Ti(x)/SBA-15 materials and that TiOx tends to form agglomerates in close proximity to the Au nanoparticles, often forming core-shell Au/TiOx structures. This behavior resembles typical processes observed due to strong-metal support interactions. In the presence of gold, the formation of hydrogen on Ti(x)/SBA-15 during the photodeposition process and the performance in the hydroxylation of terephthalic acid is greatly enhanced. The activity of the Au/Ti(x)/SBA-15 materials is found to depend on the TiOx loading, increasing with a larger amount of initially isolated TiO4 tetrahedra. Samples with initially clustered TiOx species show lower photocatalytic activities. When isolated zinc oxide (ZnOx) species are present on Ti(x)/SBA-15, gold nanoparticles are smaller and well dispersed within the pores. Agglomeration of TiOx species and the formation of Au/TiO x structures is negligible. The dispersion of gold and the formation of Au/TiOx in the SBA-15 matrix seem to depend on the mobility of the TiOx species. The mobility is determined by the initial degree of agglomeration of TiOx. Effective hydrogen evolution requires Au/TiOx core-shell composites as in Au/Ti(x)/SBA-15, whereas hydroxylation of terephthalic acid can also be performed with Au/ZnO x/TiOx/SBA-15 materials. However, isolated TiOx species have to be grafted onto the support prior to the zinc oxide species, providing strong evidence for the necessity of Ti-O-Si bridges for high photocatalytic activity in terephthalic acid hydroxylation. © 2013 American Chemical Society.

Scanning tunneling microscopy offers the exciting possibility to manipulate individual molecules by vibrational excitation via inelastically tunneling electrons. The electrons transfer energy into molecular vibrational modes, leading to breakage or formation of individual bonds. It is challenging to precisely control intramolecular changes by this process. We demonstrate that for 4,4′-dihydroxyazobenzene adsorbed on Au(111) or Ag(111), the manipulation facilitates rotation of the OH end groups around the C-O bond between metastable states; this corresponds to a reorientation of the hydrogen, the ultimate limit of a conformational change within a molecule. © 2013 American Chemical Society.

Cellulose is both insoluble in water and resistant against hydrolysis. These features pose major problems for its conversion into platform chemicals. Herein, we demonstrate that mechanocatalytic, solid-state depolymerization combined with hydrogenolysis, in the presence of Ru/C in water, provides a highly efficient pathway for the production of sugar alcohols. This novel approach leads to yields of hexitols up to 94% at 150 °C in an overall process time of 4 h. © The Royal Society of Chemistry 2013.

Water clusters have attracted a lot of attention as prototype systems to study hydrogen bonded molecular aggregates but also to gain deeper insights into the properties of liquid water, the solvent of life. All these studies depend on an accurate description of the atomic interactions and countless potentials have been proposed in the literature in the past decades to represent the potential-energy surface (PES) of water. Many of these potentials employ drastic approximations like rigid water monomers and fixed point charges, while on the other hand also several attempts have been made to derive very accurate PESs by fitting data obtained in high-level electronic structure calculations. In recent years artificial neural networks (NNs) have been established as a powerful tool to construct high-dimensional PESs of a variety of systems, but to date no full-dimensional NN PES for water has been reported. Here, we present NN potentials for water clusters containing two to six water molecules trained to density functional theory (DFT) data employing two different exchange-correlation functionals, PBE and RPBE. In contrast to other potentials fitted to first principles data, these NN potentials are not based on a truncated many-body expansion of the energy but consider the interactions between all water molecules explicitly. For both functionals an excellent agreement with the underlying DFT calculations has been found with binding energy errors of only about 1%.© by Oldenbourg Wissenschaftsverlag, München.

This paper provides an overview of objectives, structure and first results of the DEMOYS project, financially supported by the European Commission in the frame of the 7th FP - Energy. The project started on May 1, 2010 and brings together fifteen Partners, including three Universities, five Research Organizations and seven Industries. The objective of DEMOYS is the development of thin mixed conducting membranes for O2 and H2 separation by using a new deposition technique "Plasma Spraying - Thin Film" (PS-TF) in combination with nano-porous, highly catalytic layers. © 2013 The Author.

The influence of the residual growth catalyst on the reducibility and catalytic activity of Pt nanoparticles supported on oxygen- and nitrogen-functionalized CNTs (OCNTs and NCNTs) was systematically investigated. It was found that the presence of the residual growth catalyst significantly influenced the oxygen and nitrogen functionalization of CNTs, which consequently altered the reducibility of the supported Pt nanoparticles. Pt nanoparticles on NCNTs showed a higher stability against sintering in reducing atmosphere at 200 C and 400 C than those on OCNTs. On NCNTs, Pt was in a higher oxidation state and was not as easily reducible as on OCNTs. In hydrogenation catalysis, removing the residual growth catalyst is essential for the supported Pt catalyst to achieve a better performance. Compared with Pt on OCNTs, Pt on NCNTs was less active, but more selective in olefin hydrogenation due to the poisoning effect of the surface nitrogen species. © 2013 Elsevier Inc. All rights reserved.

Combining synthetic chemistry and biology: A new method that allows the incorporation of synthetic [FeFe] hydrogenase mimics into the apo-hydrogenase is highlighted. Azadithiolato-functionalized model complexes showed similar activity to wild-type enzymes when implemented into the protein. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We investigated the hydrogen embrittlement of a Fe-18Mn-1.2%C (wt.%) twinning-induced plasticity steel, focusing on the influence of deformation twins on hydrogen-assisted cracking. A tensile test under ongoing hydrogen charging was performed at low strain rate (1.7 × 10-6 s -1) to observe hydrogen-assisted cracking and crack propagation. Hydrogen-stimulated cracks and deformation twins were observed by electron channeling contrast imaging. We made the surprising observation that hydrogen-assisted cracking was initiated both at grain boundaries and also at deformation twins. Also, crack propagation occurred along both types of interfaces. Deformation twins were shown to assist intergranular cracking and crack propagation. The stress concentration at the tip of the deformation twins is suggested to play an important role in the hydrogen embrittlement of the Fe-Mn-C twining-induced plasticity steel. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The redox competition mode of scanning electrochemical microscopy (RC-SECM) was used to study the electrocatalytic activity of three different non-noble metal O2 reduction catalysts at a pH value of 7.4, namely; multi-walled carbon nanotubes (MWCNTs), cobalt protoporphyrin (CoP) and a composite of MWCNTs/CoP. The collection efficiency of a scanning electrochemical microscopy (SECM) tip for the H2O2 generated by the reduction of O2 at the catalyst layer was almost 100%. Consequently, SECM experiments in a combined redox competition and generator/collector mode could be applied for the determination of the number of electrons exchanged during O2 reduction, leading to improved understanding of the intrinsic features of catalyst activity. This approach avoids the typical limitations encountered with rotating ring disk electrode (RRDE) voltammetry, notably, the variation of the quantity of H2O2 in the proximity of the electrode with the speed of electrode rotation or the chemical decomposition of reaction intermediates on the Pt ring, which often introduce inconsistencies and errors in the measured values of the number of exchanged electrons. It is commonly assumed that the O2 reduction reaction on most non-noble metal catalysts proceeds via formation of H2O 2 as an intermediate. The follow-up reaction of H2O 2, typically chemical decomposition or electrochemical reduction, influences the overall number of electrons exchanged during O2 reduction. In this study, we have confirmed by comparing the rate of electrochemical reduction of H2O2 using rotating disk electrode (RDE) measurements with its rate of chemical decomposition studied using a positioned SECM tip, that for the MWCNTs/CoP catalyst, chemical decomposition is predominantly determining the overall number of exchanged electrons per O2 molecule. © 2012 Elsevier B.V.

The equilibrium structure including the network of hydrogen bonds of an α-chitin crystal is determined combining density-functional theory (DFT), self-consistent DFT-based tight-binding (SCC-DFTB), and empirical forcefield molecular dynamics (MD) simulations. Based on the equilibrium geometry several possible crystal conformations (local energy minima) have been identified and related to hydrogen bond patterns. Our results provide new insight and allow to resolve the contradicting α-chitin structural models proposed by various experiments. © 2012 Wiley Periodicals, Inc. Copyright © 2012 Wiley Periodicals, Inc.

A high-performance Pd catalyst for selective olefin hydrogenation was synthesized by supporting Pd nanoparticles on nitrogen-doped carbon nanotubes (NCNTs). X-ray diffraction, hydrogen chemisorption, transmission electron microscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize Pd supported on NCNTs and nitrogen-free oxygen-functionalized CNTs (OCNTs). The Pd nanoparticles were stabilized on NCNTs with narrower size distribution compared with OCNTs. The XPS analysis revealed that the nitrogen functional groups favor the reduction of Pd on CNTs suggesting an electronic promoter effect. The Pd/NCNT catalyst showed extraordinary catalytic performance in terms of activity, selectivity and stability in the selective hydrogenation of cyclooctadiene, which is related to the structural and electronic promoting effect of the NCNT support. © 2013 The Royal Society of Chemistry.

The electrocatalytic activity for oxygen reduction reaction (ORR) at neutral pH of citrate-capped silver nanoparticles (diameter = 18 nm) supported on glassy carbon (GC) is investigated voltammetrically. Novelly, the modification of the substrate by nanoparticles sticking to form a random nanoparticle array and the voltammetric experiments are carried out simultaneously by immersion of the GC electrode in an air-saturated 0.1 M NaClO4 solution (pH = 5.8) containing chemically-synthesized nanoparticles. The experimental voltammograms of the resulting nanoparticle array are simulated with homemade programs according to the two-proton, two-electron reduction of oxygen to hydrogen peroxide where the first electron transfer is rate determining. In the case of silver electrodes, the hydrogen peroxide generated is partially further reduced to water via heterogeneous decomposition. Comparison of the results obtained on a silver macroelectrode and silver nanoparticles indicates that, for the silver nanoparticles and particle coverages (0.035%-0.457%) employed in this study, the ORR electrode kinetics is slower and the production of hydrogen peroxide larger on the glassy carbon-supported nanoparticles than on bulk silver. [Figure not available: see fulltext.] © 2013 Tsinghua University Press and Springer-Verlag Berlin Heidelberg.

The crystal and molecular structure of (E)-N,N′- dicyclohexylacetamidine (1) is described. Crystalline material of 1 was obtained by sublimation. Single-crystal X-ray analysis revealed a centrosymmetric triclinic structure (space group P1̄) with six molecules in the asymmetric unit (Z′ = 6). The six crystallographically distinct molecules all exhibit an E-syn structure, but differ in the orientation of the cyclohexyl groups about the central acetamidine moiety. In the crystal, the molecules form polymeric helices via NH⋯N hydrogen bonds. The crystal structure comprises two crystallographically distinct helices of opposite handedness (P and M form). The characterisation of 1 in the solid-state is augmented by powder X-ray diffraction, infrared spectroscopy and thermal analysis. Density functional theory (DFT) structure optimisation and frequency calculation were performed at the B3LYP/cc-pVTZ level. The DFT results for the isolated molecule are compared with the experimental results for the solid-state. © 2012 Elsevier B.V. All rights reserved.

A white Mo(VI)-melamine hybrid solid precipitated immediately when aqueous solutions of (NH4)6Mo7O24 and melamine were mixed. This hybrid proved to be an efficient single-source precursor for single-phase β-Mo2C. Treating the precursor at 650 C in either Ar or H2 resulted in molybdenum carbides, with H 2 being the optimal choice from the perspective of achieving a high-purity carbide. This single-source route successfully inverted the direction of carbon diffusion, thus alleviating the polymerization of carbon species on the carbide surface, which will provide several advantages in catalytic applications. As in the hydrogenation of naphthalene, an ultrahigh selectivity to tetralin was achieved over the resultant β-Mo2C, and its highly purified surface facilitated a steady state with high conversion. With the characteristics of low cost and nontoxicity, the Mo(VI)-melamine hybrid could serve as a green starting material for obtaining highly crystallized β-Mo2C with high purity. © 2013 American Chemical Society.

Carbide-derived carbon (CDC) monoliths (DUT-38) with a distinctive macropore network are physically activated using carbon dioxide as oxidizing agent. This procedure is carried out in a temperature range between 850 and 975 °C with durations ranging from 2 to 6 h. Resulting materials show significantly increased specific surface areas as high as 3100 m2/g and total (micro/meso) pore volumes of more than 1.9 cm3/g. The methane (214 mg/g at 80 bar/25 °C), hydrogen (55.6 mg/g at 40 bar/-196 °C), and n-butane (860 mg/g at 77 vol.%/25 °C) storage capacities of the activated CDCs are significantly higher as compared to the non-activated reference material. Moreover, carbon dioxide activation is a suitable method for the removal of metal chlorides and chlorine residuals adsorbed in the pores of CDC after high temperature chlorination. The activation does not influence the hydrophobic surface properties of the CDCs as determined by water adsorption experiments. The macropore network and the monolithic shape of the starting materials can be fully preserved during the activation procedure. n-Butane breakthrough studies demonstrate the materials applicability as an efficient hydrophobic filter material by combining excellent materials transport with some of the highest capacity values that have ever been reported for CDCs. © 2013 Elsevier Ltd. All rights reserved.

The design of biofuel cell anodes with substantially decreased potential is a prerequisite for the development of biofuel cells with large open-circuit voltage and power density. Redox polymers with covalently attached phenothiazine derivatives such of thionine acetate, toluidine blue, azure B simultaneously providing epoxide functions for covalent binding to suitably modified electrode surfaces and crosslinking were synthesized and evaluated for their ability to transfer electrons from the FAD cofactor of the flavodehydrogenase domain of cellobiose dehydrogenase from Myriococcum thermophilum (FAD-MtCDH), the flavodehydrogenase domain of cellobiose dehydrogenase from Corynascus thermophilus (FAD-CtCDH), or glucose oxidase from Aspergillus niger (GOx). Polymer/enzyme films were covalently bound via polymer bound epoxy groups to terminal amino functions introduced to graphite electrode surfaces by electrochemically induced grafting of diaminoheptane or Boc-protected ethylene diamine (EDA). The electrodes were optimized for biocatalytic glucose oxidation with respect to the hydrophilicity of the polymer backbone, the nature of the phenothiazine derivative, the pH value, as well as the relative amount of enzyme, polymer and crosslinker. Biofuel cells based on toluidine blue-modified redox polymers with integrated FAD-MtCDH, FAD-CtCDH, or GOx in combination with a bilirubin oxidase based biocathode exhibited open-circuit voltages of more than 0.7 V and maximum power densities in the range of 4 to 6 μW cm -2 at a pH value of 7.8. © 2013 Elsevier Ltd. All rights reserved.

Constant COx-free H2 production from the catalytic decomposition of ammonia could be achieved over a high-surface-area molybdenum carbide catalyst prepared by a temperature-programmed reduction-carburization method. The fresh and used catalyst was characterized by N2 adsorption/desorption, powder X-ray diffraction, scanning and transmission electron microscopy, and electron energy-loss spectroscopy at different stages. Observed deactivation (in the first 15 h) of the high-surface-area carbide during the reaction was ascribed to considerable reduction of the specific surface area due to nitridation of the carbide under the reaction conditions. Theoretical calculations confirm that the N atoms tend to occupy subsurface sites, leading to the formation of nitride under an NH3 atmosphere. The relatively high rate of reaction (30 mmol/((g of cat.) min)) observed for the catalytic decomposition of NH3 is ascribed to highly energetic sites (twin boundaries, stacking faults, steps, and defects) which are observed in both the molybdenum carbide and nitride samples. The prevalence of such sites in the as-synthesized material results in a much higher H2 production rate in comparison with that for previously reported Mo-based catalysts. © 2013 American Chemical Society.

Oxygen- and nitrogen-functionalized carbon nanotubes (OCNTs and NCNTs) were applied as metal-free catalysts in selective olefin hydrogenation. A series of NCNTs was synthesized by NH3 post-treatment of OCNTs. Temperature-programmed desorption, N2 physisorption, Raman spectroscopy, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy were employed to characterize the surface properties of OCNTs and NCNTs, aiming at a detailed analysis of the type and amount of oxygen- and nitrogen-containing groups as well as surface defects. The gas-phase treatments applied for oxygen and nitrogen functionalization at elevated temperatures up to 600 °C led to the increase of surface defects, but did not cause structural damages in the bulk. NCNTs showed a clearly higher activity than the pristine CNTs and OCNTs in the hydrogenation of 1,5-cyclooctadiene, and also the selectivity to cyclooctene was higher. The favorable catalytic properties are ascribed to the nitrogen-containing surface functional groups as well as surface defects related to nitrogen species. In contrast, oxygen-containing surface groups and the surface defects caused by oxygen species did not show clear contribution to the hydrogenation catalysis. Copyright © 2013, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.

Design and fabrication of semiconductor based composite photocatalysts with matching band structure is an important strategy to improve charge separation of photogenerated electron-hole pairs for photocatalytic hydrogen production. In our study, by aid of the simple and cost-effective molten salts method, a series of phase-controlled and composition-tuned calcium tantalate composite photocatalysts has been prepared by adjusting the initial atomic ratio of Ta/Ca precursors. We demonstrate the strong correlation between the photocatalytic activities of calcium tantalate composite photocatalysts for hydrogen evolution and respective phase compositions. Without any cocatalysts, these composites with the optimized phase composition of cubic α-CaTa2O 6/hexagonal Ca2Ta2O7, cubic CaTa2O6/hexagonal Ca2Ta2O 7/orthorhombic β-CaTa2O6, or cubic α-CaTa2O6/orthorhombic β-CaTa2O 6 showed very high photocatalytic H2 production activities in the presence of methanol. It is attributed mainly to a significantly improved photoexcited charge carrier separation via the junctions and interfaces in the composites. Further by in situ photodeposition of noble metal nanoparticles (Pt or Rh) as cocatalysts the photocatalytic activity of these composites was greatly promoted for H2 production. The study on convenient fabrication of phase-coexisting composite photocatalysts with matching band structure for improving the photocatalytic hydrogen production sheds light on developing efficient composite photocatalyst as a means for conversion of solar energy to chemical energy. © 2013 American Chemical Society.

A direct strategy for the creation of defects on carbon nanofibers (CNFs) has been developed by steam treatment. Nitrogen physisorption, XRD, Raman spectra, SEM and TEM analyses proved the existence of the new defects on CNFs. BET surface area of CNFs after steam treatment was enhanced from 20 to 378 m2/g. Pd catalysts supported on CNFs were also prepared by colloidal deposition method. The different activity of Pd/CNFs catalysts in the partial hydrogenation of phenylacetylene further demonstrated the diverse surfaces of CNFs could be formed by steam treatment. © 2013 Dalian Institute of Chemical Physics, the Chinese Academy of Sciences. Published by Elsevier B.V.

Pyrdine incorporation into the covalent organic framework COF-1 resulted in a highly dense packing structure in which the pyridine occupies the hexagonal pore space between the COF layers. This optimizes pore aperture for quantum sieving of hydrogen isotopes and introduces flexibility at cryogenic temperatures into the system. The separation factor (S D 2/H 2) is about 10 at 22K, which is the highest reported to date. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The CALPHAD method was employed to assess the austenite stability of model alloys based on the Cr-Mn-Ni-Cu system. Stability was evaluated as the difference in Gibbs free energy between the austenite and ferrite phases. This energy difference represents the chemical driving force for the martensitic transformation and is employed as a design criterion. Six novel alloys featuring a lower driving force compared to the reference material AISI 316L were produced in laboratory. The susceptibility of all alloys to hydrogen gas embrittlement was evaluated by slow strain-rate tensile testing in air and hydrogen gas at 40 MPa and -50 C. The mechanical properties and ductility response of four of the six alloys exhibited an equivalent performance in air and hydrogen. Thermodynamic calculations were in agreement with the amount of α′-martensite formed during testing. Furthermore, a 4.5 wt.% reduction in the nickel content in comparison to 316L promises a cost benefit for the novel materials. © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Newly synthesised osmium complex-modified redox polymers were tested for potential application as mediators in glucose oxidising enzyme electrodes for application to biosensors or biofuel cells. Coupling of osmium complexes containing amine functional groups to epoxy-functionalised polymers of variable composition provides a range of redox polymers with variation possible in redox potential and physicochemical properties. Properties of the redox polymers as mediators for glucose oxidation were investigated by co-immobilisation onto graphite with glucose oxidase or FAD-dependent glucose dehydrogenase using a range of crosslinkers and in the presence and absence of multiwalled carbon nanotubes. Electrodes prepared by immobilising [P20-Os(2,2'-bipyridine)2(4-aminomethylpyridine)Cl].PF6, carbon nanotubes and glucose oxidase exhibit glucose oxidation current densities as high as 560μAcm-2 for PBS containing 100mM glucose at 0.45V vs. Ag/AgCl. Films prepared by crosslinking [P20-Os(4,4'-dimethoxy-2,2'-bipyridine)2(4-aminomethylpyridin e)Cl].PF6, an FAD-dependent glucose dehydrogenase, and carbon nanotubes achieve current densities of 215μAcm-2 in 5mM glucose at 0.2V vs. Ag/AgCl, showing some promise for application to glucose oxidising biosensors or biofuel cells. © 2012 Elsevier B.V.

A novel high-aluminum austenitic stainless steel has been produced in the laboratory with the aim of developing a lean-alloyed material with a high resistance to hydrogen environment embrittlement. The susceptibility to hydrogen environment embrittlement was evaluated by means of tensile tests at a slow strain rate in pure hydrogen gas at a pressure of 40 MPa and a temperature of -50 C. Under these conditions, the yield strength, tensile strength and elongation to rupture are not affected by hydrogen in comparison to companion tests carried out in air. Moreover, a very high ductility in hydrogen is evidenced by a reduction of area of 70% in the high-pressure and low-temperature hydrogen environment. The lean degree of alloying is reflected in the molybdenum-free character of the material and a nickel content of 8.0 wt.%. With regard to the alloy concept, a combination of high-carbon, high-manganese, and high-aluminum contents confer an extremely high stability against the formation of strain-induced martensite. This aspect was investigated by means of in-situ magnetic measurements and ex-situ X-ray diffraction. The overall performance of the novel alloy was compared with two reference materials, 304L and 316L austenitic stainless steels, both industrially produced. Its capability of maintaining a fully austenitic structure during tensile testing has been identified as a key aspect to avoid hydrogen environment embrittlement. Copyright © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

A pH-dependent, two-electron transfer redox polymer was synthesized based on a methacrylate backbone with tunable properties covalently modified with toluidine blue (P017-TB). Entrapment of the isolated flavodehydrogenase domain of cellobiose dehydrogenase from Myriococcum thermophilum (FAD-MtCDH) within P017-TB is the basis for low-potential bioanode with an open circuit potential of - 240 mV vs. Ag/AgCl and a maximum current density of 60 μA cm - 2 at - 150 mV. Together with a bilirubin oxidase biocathode a biofuel cell with an open circuit voltage of 720 mV and a power density of 6.1 μW cm- 2 was obtained. © 2013 Elsevier B.V.

The influence of Cs + and Na + on the adsorption of *H, *OH, and *O (where * denotes adsorbed species) at polycrystalline Pt in acidic sulfuric media has been investigated. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry, and electrochemical nanogravimetry were used (i) to elucidate the models of the interface between polycrystalline Pt and the electrolytes in a wide range of electrode potentials and (ii) to resolve contributions originating from adsorbed *H, (bi)sulfate, *OH, and *O as well as the cations to the overall interface status. Using impedance analysis it was possible to separate at least two adsorption processes: (bi)sulfate and hydrogen adsorption. The nanogravimetry additionally resolves the contribution from Cs +. Specific adsorption of Cs + at Pt surface significantly affects hydrogen adsorption, while it has almost no effect on the dynamics of SO 4 2- adsorption. Specifically adsorbed alkali cations, however, are desorbed by the onset of *OH(*O) adsorption at the Pt surface. Nevertheless, the cations likely remain in the close proximity to the surface, probably in the second H 2O layer, and largely contribute to the formation of the *OH and *O adsorbed species originating from the surface water. © 2012 American Chemical Society.

The deposition of hydrogen evolution sites on photocatalysts is a crucial step in the multistep process of synthesizing a catalyst that is active for overall photocatalytic water splitting. An alternative approach to conventional photodeposition was developed, applying the photocatalytic reforming of aqueous methanol solutions to deposit metal particles on semiconductor materials such as Ga2O3 and (Ga0.6Zn0.4)(N 0.6O0.4). The method allows optimizing the loading of the co-catalysts based on the stepwise addition of their precursors and the continuous online monitoring of the evolved hydrogen. Moreover, a synergetic effect between different co-catalysts can be directly established. © 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Iron oxide is a key multi-functional material in many different fields of modern technology. The β-Fe2O3 cubic phase, one of the least studied Fe-O systems, was obtained by Chemical Vapor Deposition (CVD) using for the first time a Fe(ii) β-diketonate diamine complex, Fe(hfa)2·TMEDA, as the molecular source (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA = N,N,N′,N′- tetramethylethylenediamine). The strong visible light absorption of β-Fe2O3 deposits highlights their possible functional application in photocatalytic hydrogen production under solar light. A comprehensive investigation on the Fe(ii) complex, performed by a joint experimental-theoretical approach, explains the molecular origin of its excellent thermal behaviour and reveals why this species is a successful precursor for the CVD of iron oxide nanostructures. © The Royal Society of Chemistry.

ORR MNC, FTW! Mesoporous nitrogen-rich carbon (MNC) materials are synthesized by using polymer-loaded SBA-15 pyrolyzed at different temperatures. The activity and stability of the catalysts in the oxygen reduction reaction (ORR) are investigated by using cyclic voltammetry and rotating-disk electrode measurements. The MNC material pyrolyzed at 800 °C exhibits a high electrocatalytic activity towards the ORR in alkaline medium. © 2012 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim.

Two aspartate protease encoding complementary deoxyribonucleic acids (cDNA) were characterised from the small intestine (posterior midgut) of Triatoma infestans and the corresponding genes were named TiCatD and TiCatD2. The deduced 390 and 393 amino acid sequences of both enzymes contain two regions characteristic for cathepsin D proteases and the conserved catalytic aspartate residues forming the catalytic dyad, but only TiCatD2 possesses an entire C-terminal proline loop. The amino acid sequences of TiCatD and TiCatD2 show 51-58% similarity to other insect cathepsin D-like proteases and, respectively, 88 and 58% similarity to the aspartate protease ASP25 from T. infestans available in the GenBank database. In phylogenetic analysis, TiCatD and ASP25 clearly separate from cathepsin D-like sequences of other insects, TiCatD2 groups with cathepsin D-like proteases with proline loop. The activity of purified TiCatD and TiCatD2 was highest between pH 2 and 4, respectively, and hence, deviate from the pH values of the lumen of the small intestine, which varied in correlation with the time after feeding between pH 5.2 and 6.7 as determined by means of micro pH electrodes. Both cathepsins, TiCatD and TiCatD2, were purified from the lumen of the small intestine using pepstatin affinity chromatography and identified by nanoLC-ESI-MS/MS analysis as those encoded by the cDNAs. The proteolytic activity of the purified enzymes is highest at pH 3 and the respective genes are expressed in the both regions of the midgut, stomach (anterior midgut) and small intestine, not in the rectum, salivary glands, Malpighian tubules or haemocytes. The temporal expression pattern of both genes in the small intestine after feeding revealed a feeding dependent regulation for TiCatD but not for TiCatD2. © 2011 Elsevier Ltd.

Electrocatalytic NADH oxidation was investigated at an electrode architecture involving an electropolymerized layer of poly(methylene blue) (pMB) or poly(methylene green) (pMG) in combination with specifically designed toluidine blue or nile blue modified methacrylate-based electrodeposition polymers. Either NAD +-dependent lactate dehydrogenase or NAD +-dependent glucose dehydrogenase were entrapped between the primary electropolymerized layer of pMB or pMG and the methacrylate-based redox polymer. The composition of the polymer backbone and the polymer-bound redox dye was evaluated and it could be demonstrated that the combination of the electropolymerized pMB or pMG layer together with the dye modified methacrylate-based redox polymer shows superior properties as compared with either of the components alone. NADH was oxidized at an applied potential of 0 mV vs Ag/AgCl/KCl 3 M and current densities of 17 μA·cm -2 and 28 μA·cm -2 were obtained for modified electrodes based on lactate dehydrogenase and glucose dehydrogenase, respectively, at substrate saturation. © 2012 Springer-Verlag.

The reaction path of the Cl 2 evolution reaction (CER) was investigated by combining electrochemical and spectroscopic methods. It is shown that oxidation and reconstruction of the catalyst surface during CER is a consequence of the interaction between RuO 2 and water. The state of the RuO 2 surface during the electrochemical reaction was analyzed in situ by using Raman spectroscopy to monitor vibrations of the crystal lattice of RuO 2 and changes in the surface concentration of the adsorbed species as a function of the electrode potential. The role of the solvent was recognized as being crucial in the formation of an oxygen-containing hydrophilic layer, which is a key prerequisite for electrocatalytic Cl 2 formation. Water (more precisely the OH adlayer) is understood not just as a medium that allows adsorption of intermediates, but also as an integral part of the intermediate formed during the electrochemical reaction. New insights into the general understanding of electrocatalysis were obtained by utilizing the vibration frequencies of the crystal lattice as a dynamic catalytic descriptor instead of thermodynamic descriptors, such as the adsorption energy of intermediates. Interpretation of the derived "volcano" curve suggests that electrocatalysis is governed by a resonance phenomenon. Water powered! The reaction path of the Cl 2 evolution reaction (CER) is investigated by combining electrochemical and spectroscopic methods. Oxidation and reconstruction of the catalyst surface during CER is a consequence of the interaction between RuO 2 and water. Interpretation of the derived volcano curve suggests that electrocatalysis is governed by a resonance phenomenon (see picture). © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The extent of hydrogen embrittlement in steel depends strongly on the H distribution in the microstructure. Alloying elements might serve to detract hydrogen from regions prone to embrittlement and to distribute it within areas where it causes less damage. We present an ab initio study of the interaction of interstitial hydrogen in α-iron with substitutional transition-metal atoms as alloying elements. We find similar trends for the 3d, 4d, and 5d transition metal elements: the elements in the middle of the transition-metal series repel hydrogen while those on the sides tend to attract hydrogen. The trend is in line with the volume change that the transition-metal solute atom exerts on the iron lattice. The interaction energy decreases rapidly with separation distance with a range of approximately 5 . We use a simple parametrisation in order to estimate finite-size effects in the ab initio data. © 2012 Elsevier B.V. All rights reserved.

Structural defects in materials such as vacancies, grain boundaries, and dislocations may trap hydrogen and a local accumulation of hydrogen at these defects can lead to the degradation of the materials properties. An important aspect in obtaining insight into hydrogen-induced embrittlement on the atomistic level is to understand the diffusion of hydrogen in these materials. In our study we employ kinetic Monte Carlo (kMC) simulations to investigate hydrogen diffusion in bcc iron within different microstructures. All input data to the kMC model, such as available sites, solution energies, and diffusion barriers, are obtained from first-principles calculations. We find that hydrogen mainly diffuses within the interface region with an overall diffusivity that is lower than in pure bcc Fe bulk. The concentration dependence of the diffusion coefficient is strongly nonlinear and the diffusion coefficient may even decrease with an increasing hydrogen concentration. To describe the macroscopic diffusion coefficient we derive an analytic expression as a function of hydrogen concentrations and temperatures which is in excellent agreement with our numerical results for idealized microstructures. © 2012 American Physical Society.

Spectroscopic identification and characterization of covalent and noncovalent intermediates on large enzyme complexes is an exciting and challenging area of modern enzymology. The Escherichia coli pyruvate dehydrogenase multienzyme complex (PDHc), consisting of multiple copies of enzymic components and coenzymes, performs the oxidative decarboxylation of pyruvate to acetyl-CoA and is central to carbon metabolism linking glycolysis to the Krebs cycle. On the basis of earlier studies, we hypothesized that the dynamic regions of the E1p component, which undergo a disorder-order transition upon substrate binding to thiamin diphosphate (ThDP), play a critical role in modulation of the catalytic cycle of PDHc. To test our hypothesis, we kinetically characterized ThDP-bound covalent intermediates on the E1p component, and the lipoamide-bound covalent intermediate on the E2p component in PDHc and in its variants with disrupted active-site loops. Our results suggest that formation of the first covalent predecarboxylation intermediate, C2α-lactylthiamin diphosphate (LThDP), is rate limiting for the series of steps culminating in acetyl-CoA formation. Substitutions in the active center loops produced variants with up to 900-fold lower rates of formation of the LThDP, demonstrating that these perturbations directly affected covalent catalysis. This rate was rescued by up to 5-fold upon assembly to PDHc of the E401K variant. The E1p loop dynamics control covalent catalysis with ThDP and are modulated by PDHc assembly, presumably by selection of catalytically competent loop conformations. This mechanism could be a general feature of 2-oxoacid dehydrogenase complexes because such interfacial dynamic regions are highly conserved. © 2012 American Chemical Society.

Hydrogen embrittlement was observed in an Fe-18Mn-1.2C (wt.%) steel. The tensile ductility was drastically reduced by hydrogen charging during tensile testing. The fracture mode was mainly intergranular fracture, though transgranular fracture was also partially observed. The transgranular fracture occurred parallel to the primary and secondary deformation twin boundaries, as confirmed by electron backscattering diffraction analysis and orientation-optimized electron channeling contrast imaging. The microstructural observations indicate that cracks are initiated at grain boundaries and twin boundaries. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The organization of water at the interface with silica and alumina oxides is analysed using density functional theory-based molecular dynamics simulation (DFT-MD). The interfacial hydrogen bonding is investigated in detail and related to the chemistry of the oxide surfaces by computing the surface charge density and acidity. We find that water molecules hydrogen-bonded to the surface have different orientations depending on the strength of the hydrogen bonds and use this observation to explain the features in the surface vibrational spectra measured by sum frequency generation spectroscopy. In particular, ice-like and liquid-like features in these spectra are interpreted as the result of hydrogen bonds of different strengths between surface silanols/aluminols and water. © 2012 IOP Publishing Ltd.

A non-syngas direct steam reforming route is investigated for the conversion of methanol to hydrogen and carbon dioxide over a CuZnGaOx catalyst at 150-200 °C. This route is in marked contrast with the conventional complex route involving steam reformation to syngas (CO/H 2) at high temperature, followed by water gas shift and CO cleanup stages for hydrogen production. Here we report that high quality hydrogen and carbon dioxide can be produced in a single-step reaction over the catalyst, with no detectable CO (below detection limit of 1 ppm). This can be used to supply proton exchange membrane fuel cells for mobile applications without invoking any CO shift and cleanup stages. The working catalyst contains, on average, 3-4 nm copper particles, alongside extremely small size of copper clusters stabilized on a defective ZnGa2O4 spinel oxide surface, providing hydrogen productivity of 393.6 ml g-1-cat h-1 at 150 °C. © 2012 Macmillan Publishers Limited. All rights reserved.

Multiwalled carbon nanotubes (MWCNT) have been functionalized, for the electrocatalytic detection of NADH, by microwave treatment, electrochemical deposition of poly(methylene green) or wrapping with an Os-complex modified polymer. Sol-gel thin films have been then electrodeposited on the carbon nanotube layers for co-immobilization of D-sorbitol dehydrogenase and diaphorase when necessary and NAD + via covalent linkage using glycidoxypropyltrimethoxysilane. The comparison of these systems shows that the electrodeposited sol-gel matrix can significantly affect the operational behavior of functionalized MWCNT. Only MWCNT wrapped with the Os-complex modified polymer and covered with a sol-gel biocomposite allowed the electrochemical detection of D-sorbitol in a reagentless configuration. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Seven stable austenitic steels (stable with respect to γ → α′ transformation at room temperature) of different alloy compositions (18Cr-12.5Ni, 18Cr-35Ni, 18Cr-8Ni-6Mn-0.25N, 0.6C-23Mn, 1.3C-12Mn, 1C-31Mn-9Al, 18Cr-19Mn-0.8N) were tensile tested in high-pressure hydrogen atmosphere to assess the role of austenite stability on hydrogen environment embrittlement (HEE). The influence of hydrogen on tensile ductility was small in steels that are believed to have a high initial portion of dislocation cross slip (18Cr-12.5Ni, 18Cr-35Ni, 18Cr-8Ni-6Mn-0.25N), while the effects of hydrogen were significantly greater in steels with other primary deformation modes (planar slip in 18Cr-19Mn-0.8N and 1C-31Mn-9Al or mechanical twinning in 0.6C-23Mn and 1.3C-12Mn) despite comparable austenite stability at the given test conditions. It appears that initial deformation mode is one important parameter controlling susceptibility to HEE and that martensitic transformation is not a sufficient explanation for HEE of austenitic steels. Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Pt-based alloys containing Rh and Ru are effective catalysts in a range of applications, including pollution control and low-temperature fuel cells. As the Pt group metals are generally rare and expensive, minimizing the loading of them while also increasing the efficiency of catalyst materials is a continual challenge in heterogeneous catalysis. A smart method to "nanoengineer" the surface of the nanocatalyst particles would greatly aid this goal. In our study, the oxidation of a Pt-8.9 at. % Ru alloy between 773 and 973 K and the oxidation and oxidation/reduction behavior of a Pt-23.9 at. % Rh-9.7 at. % Ru alloy at 873 K for various exposure times were studied using atom probe tomography. The surface of the Pt-Ru alloy is enriched with Ru after oxidation at 773 K, whereas it is depleted in Ru at 873 K, and at 973 K. The surface oxide layer vanishes at higher temperatures, leaving behind a Pt-rich surface. In the case of the Pt-Rh-Ru alloy, oxidation initiates from the grain boundaries, forming an oxide with a stoichiometry of MO 2. As the oxidation time increases, this oxide evolves into a twophase nanostructure, involving a Rh-rich oxide phase (Rh, Ru) 2O 3 and a Ru-rich oxide phase (Ru, Rh)O 2. When this two-phase oxide is reduced in hydrogen at low temperatures, separate Rh-rich and Ru-rich nanoscale regions remain. This process could, therefore, be useful for synthesizing complex island structures on Pt-Rh-Ru nanoparticle catalysts. © 2012 American Chemical Society.

The electrochemical co-deposition of iron and gallium from a simple aqueous electrolyte was investigated by means of the electrochemical quartz crystal microbalance technique. The results reveal that alloy deposition occurs at potentials more positive than the deposition potential of single gallium. At the same time, large amounts of hydroxides are chemically precipitated due to a pH increase caused by strong hydrogen evolution. If the pH increase is compensated by applying potential pulses, these hydroxides are re-dissolved and metallic alloy films with low oxygen content are directly accessible. XPS and TEM investigations confirm the formation of an Fe100-xGax alloy (x = 20 ± 4 at.%). © 2012 The Electrochemical Society.

Platinum group metals (PGMs) are used in numerous catalyst applications, including conversion of engine exhaust gases and hydrocarbon reforming. Reducing the loading of PGMs without diminishing the overall catalyst activity is a major challenge. Fundamental studies of PGMs under reactive conditions can assist the design/synthesis of "nanoengineered" catalysts, tunable and optimized for cost, stability, and performance. In the present study, the oxidation and reduction behavior of a Pd-6.4 at. % Rh alloy is investigated following treatment at 873 K for various exposure times using atom-probe tomography. For short oxidation times (10 min), an oxide layer with PdO stoichiometry grows on the surface. As the oxidation time increases, two phases with stoichiometries of (Rh 1Pd 1)O 2 and (Pd 2O) evolve. When the alloy is subsequently reduced in hydrogen, a nanoscale dispersion of Rh-rich metallic regions remains. This provides a route for the synthesis of multifunctional catalysts with different nanosurface regions in close proximity to one another. © 2012 American Chemical Society.

High-energy-resolution fluorescence-detected X-ray absorption spectroscopy (HERFD-XAS) has been applied to study the chemical state of ∼1.2 nm size-selected Pt nanoparticles (NPs) in an electrochemical environment under potential control. Spectral features due to chemisorbed hydrogen, chemisorbed O/OH, and platinum oxides can be distinguished with increasing potential. Pt electro-oxidation follows two competitive pathways involving both oxide formation and Pt dissolution. © 2012 American Chemical Society.

In this work, wet ball milling with Tetrahydrofuran (THF) was applied to activate the LiNH2+1.2LiH hydrogen storage system. Based on this, the effect of boron nitride additives was studied. Compared to dry ball milled samples, the wet ball milled material showed similar particle and crystallite size. While an additional 24 hours wet ball milling with fine milling ball process reduced the particle size obviously. The recyclability of this hydrogen storage system was enhanced significantly by an additive of 3 wt. % boron nitride, while particle and crystallite size were not influenced after milling. © 2012 Published by Elsevier Ltd.

Metal oxides such as ZnO have been used as hydrogen sensors for a number of years. Through doping, the gas response of zinc oxide to hydrogen has been improved. Cadmium-doped ZnO nanowires (NWs) with high aspect ratio have been grown by electrodeposition. Single doped ZnO NWs have been isolated and contacted to form a nanodevice. Such nanosystem demonstrates an enhanced gas response and selectivity for the detection of hydrogen at room temperature compared to previously reported H 2 nanosensors based on pure single-ZnO NWs or multiple NWs. A dependence of the gas response of a single Cd-ZnO nanowire on the NW diameter and Cd content was observed. It is shown that cadmium-doping in single-crystal zinc oxide NWs can be used to optimize their response to gases without the requirement of external heaters. The sensing mechanisms responsible for such improved response to hydrogen are discussed. © 2012 Elsevier B.V.

Based on first-principles calculations, we identify a master curve for the solution enthalpy of H in fourth row elements including all 3d transition metals. Assuming nonmagnetic fcc crystal structures, we find two different classes of materials with either the octahedral or the tetrahedral interstitial site being preferred by hydrogen. An interaction radius for H in octahedral site of ≈0.7 Å (≈0.4Å for H in tetrahedral site) turns out to be a characteristic value for which the chemical interaction energy has an optimum for all studied elements. © 2012 American Physical Society.

The sintering of iron nanoparticles on carbon nanotubes (CNTs) under different atmospheres was investigated. CNTs were first treated with HNO3 vapor at 200°C to obtain O-functionalized CNTs (OCNTs). The OCNTs were treated in ammonia at 400°C to obtain N-doped CNTs (NCNTs). Highly dispersed FeOx nanoparticles were subsequently deposited by chemical vapor deposition from ferrocene under oxidizing conditions. The obtained FeOx/OCNT and FeOx/NCNT samples were allowed to sinter at 500°C under flowing helium, hydrogen, or ammonia. The samples were studied by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. A significant increase in particle size and a decrease in Fe surface atomic concentration were observed in all the sintered samples. The sintering on OCNTs was more severe than on NCNTs, which can be attributed to stronger metal-substrate interactions and a higher amount of surface defects on NCNTs. The applied gas atmosphere had a substantial influence on the sintering behavior of the nanoparticles: treatment in helium led to the growth of particles and a significant widening of particle size distributions, whereas treatment in hydrogen or ammonia resulted in the growth of particles, but not in the widening of particle size distributions. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hydrogen environment embrittlement of metastable austenitic stainless steels is a well-known phenomenon partially related to the formation of straininduced martensite. In the literature, hydrogen environment embrittlement is often discussed on the basis of nominal chemical compositions only and neglects effects of metallurgical production and processing. The aim of this study is to investigate the influence of the d-ferrite volume fraction and grain size on the mechanical properties of a standard grade 1.4307 (AISI 304L) tested in high-pressure hydrogen gas. A negligible influence was found for dferrite volume fractions between 2 and 10 %. This result is explained by the dominating influence of machininginduced a-martensite on the surface of the tensile samples. In contrast, the grain size was found to have a significant effect on hydrogen environment embrittlement. In particular, grain sizes smaller than 50 lm were found to have a higher ductility. The results are discussed with respect to stacking fault energy, formation of strain-induced a-martensite, trapping of hydrogen and microsegregations. The results are of particular interest for the materials selection and development of materials for hydrogen applications. © Springer Science+Business Media, LLC 2012.

Hydrogen gas is believed to play a more important role for energy supply in future instationary and mobile applications. In most cases, metallic materials are embrittled when hydrogen atoms are dissolved interstitially into their lattice. Concerning steels, in particular the ductility of ferritic grades is degraded in the presence of hydrogen. In contrast, austenitic steels usually show a lower tendency to hydrogen embrittlement. However, the so-called "metastable" austenitic steels are prone to hydrogen environmental embrittlement (HEE), too. Here, AISI 304 type austenitic steel was tensile tested in air at ambient pressure and in a 400 bar hydrogen gas atmosphere at room temperature. The screening of different alloys in the compositional range of the AISI 304 standard was performed with the ambition to optimize alloying for hydrogen applications. The results of the mechanical tests reveal the influence of the alloying elements Cr, Ni, Mn and Si on HEE. Besides nickel, a positive influence of silicon and chromium was found. Experimental results are supported by thermodynamic equilibrium calculations concerning austenite stability and stacking fault energy. All in all, the results of this work are useful for alloy design for hydrogen applications. A concept for a lean alloyed austenitic stainless steel is finally presented. © 2012 Trans Tech Publications, Switzerland.

Complex Eu(AlH 4) 2 and Sr(AlH 4) 2 hydrides have been prepared by a mechanochemical metathesis reaction from NaAlH 4 and europium or strontium chlorides. The crystal structures were solved from powder X-ray diffraction data in combination with solid-state 27Al NMR spectroscopy. The thermolysis pathway was analyzed in detail, allowing identification of new intermediate EuAlH 5/SrAlH 5 compounds. Rehydrogenation experiments indicate that the second decomposition step is reversible. © 2012 American Chemical Society.

Hierarchical porous carbide-derived carbon monoliths (HPCDCM) were prepared by selective extraction of silicon from ordered mesoporous silicon carbide monoliths (OMSCM) through chlorination at high temperature. The OMSCM was firstly synthesized by pressure-assisted nanocasting procedure using KIT-6 silica as the hard template and polycarbosilane (PCS-800) as the preceramic precursor. The OMSCM showed cubic ordered mesoporous structure with specific surface area of over 600 m 2 g -1. After the chlorination, the resulting HPCDCM demonstrated very high specific surface area (2933 m 2 g -1), large pore volume (2.101 cm 3 g -1) with large volume of micropores (0.981 cm 3 g -1), and narrow dual pore size distributions (micropore: 0.9 nm, and mesopore: 3.1 nm). Macropores in the micron range were observed in the HPCDCM. The mesostructural ordering was not maintained in the HPCDCM and the volume of the HPCDCM had greatly shrunk, by 21.2% compared to that of the OMSCM, but the tablet-like appearance was well retained in the HPCDCM. At -196 °C, the HPCDCM shows good hydrogen uptakes of 2.4 wt% and 4.4 wt% at 1 bar and 36 bar, respectively. The calculated volumetric hydrogen storage capacity is 11.6 g L -1 at 36 bar. The gravimetric hydrogen uptake capacity of the HPCDCM is comparable to, or higher than, those of previously reported ordered mesoporous carbide-derived carbon (CDC) powder and microporous CDC powder. © The Royal Society of Chemistry 2012.

Scanning electrochemical microscopy (SECM) has been established as a powerful technique in fuel cell catalysis research and development. This chapter presents the principles of SECM with a focus on the application of the various SECM modes to the investigation of fuel cell electrocatalysts. For the two most important reactions, namely hydrogen oxidation and oxygen reduction, an overview is given of kinetic studies as well as efforts in catalyst development and testing. Other reactions such as methanol oxidation and hydrogen peroxide formation and the application of SECM to fuel cell electrodes are also discussed. © 2012 Woodhead Publishing Limited All rights reserved.

Knowledge of the state of ionization and tautomerization of heteroaromatic cofactors when enzyme-bound is essential for formulating a detailed stepwise mechanism via proton transfers, the most commonly observed contribution to enzyme catalysis. In the bifunctional coenzyme, thiamin diphosphate (ThDP), both aromatic rings participate in catalysis, the thiazolium ring as an electrophilic covalent catalyst and the 4″-aminopyrimidine as acid-base catalyst involving its 1″,4″-iminopyrimidine tautomeric form. Two of four ionization and tautomeric states of ThDP are well characterized via circular dichroism spectral signatures on several ThDP superfamily members. Yet, the method is incapable of providing information about specific proton locations, which in principle may be accessible via NMR studies. To determine the precise ionization/tautomerization states of ThDP during various stages of the catalytic cycle, we report the first application of solid-state NMR spectroscopy to ThDP enzymes, whose large mass (160,000-250,000 Da) precludes solution NMR approaches. Three de novo synthesized analogues, [C2,C6″- 13C 2]ThDP, [C2- 13C]ThDP, and [N4″- 15N]ThDP used with three enzymes revealed that (a) binding to the enzymes activates both the 4″-aminopyrimidine (via pK a elevation) and the thiazolium rings (pK a suppression); (b) detection of a pre-decarboxylation intermediate analogue using [C2,C6″- 13C 2]ThDP, enables both confirmation of covalent bond formation and response in 4″-aminopyrimidine ring's tautomeric state to intermediate formation, supporting the mechanism we postulate; and (c) the chemical shift of bound [N4″- 15N]ThDP provides plausible models for the participation of the 1″,4″-iminopyrimidine tautomer in the mechanism. Unprecedented detail is achieved about proton positions on this bifunctional coenzyme on large enzymes in their active states. © 2011 American Chemical Society.

A hard hydrocarbon film is deposited on the inner surface of glass tubes using a filamentary discharge at atmospheric pressure in Ar-C 2H 2-H 2 and Ar-CH 4 mixtures. Under similar conditions, a soft film is deposited with a high deposition rate in an Ar-C 2H 2 mixture. These differences in film hardness and deposition rate are interpreted on the basis of carbon and hydrogen elemental composition in the plasma. The deposition rate is varied along the axis of the tubes in the Ar-C 2H 2-H 2 plasma. This can be controlled by controlling the substrate (tube) temperature. Chemical erosion of the deposited film by hydrogen atoms is the probable reason for this effect. The plasma conditions (gas temperature, electron distribution function and electron density) are characterized by applying optical emission spectroscopy (OES), microphotography and numerical simulation for all three gas mixtures. The density of hydrogen atoms in the inter-electrode region of the tube is determined by applying OES in all gas mixtures. The rates of precursor molecule excitation and follow-up plasma-chemical reactions are calculated on the basis of the determined plasma parameters. Correlations between plasma conditions and film properties are discussed. © 2012 IOP Publishing Ltd.

The selective hydrogenation of naphthalene to tetralin has been conducted on Mo2C/AC prepared by microwave irradiation, and achieved a lasting high conversion with 100% selectivity up to 60 hours. The choice of activated carbon as a support is critical in gaining an ideal balance between high activity and good stability of the catalyst. © 2012 The Royal Society of Chemistry.

The thermochemical constants for the oxidation of tyrosine and tryptophan through proton coupled electron transfer in aqueous solution have been computed applying a recently developed density functional theory (DFT) based molecular dynamics method for reversible elimination of protons and electrons. This method enables us to estimate the solvation free energy of a proton (H+) in a periodic model system from the free energy for the deprotonation of an aqueous hydronium ion (H3O+). Using the computed solvation free energy of H+ as reference, the deprotonation and oxidation free energies of an aqueous species can be converted to pKa and normal hydrogen electrode (NHE) potentials. This conversion requires certain thermochemical corrections which were first presented in a similar study of the oxidation of hydrobenzoquinone [J. Cheng, M. Sulpizi, and M. Sprik, J. Chem. Phys. 131, 154504 (2009)]10.1063/1.3250438. Taking a different view of the thermodynamic status of the hydronium ion, these thermochemical corrections are revised in the present work. The key difference with the previous scheme is that the hydronium is now treated as an intermediate in the transfer of the proton from solution to the gas-phase. The accuracy of the method is assessed by a detailed comparison of the computed pKa, NHE potentials and dehydrogenation free energies to experiment. As a further application of the technique, we have analyzed the role of the solvent in the oxidation of tyrosine by the tryptophan radical. The free energy change computed for this hydrogen atom transfer reaction is very similar to the gas-phase value, in agreement with experiment. The molecular dynamics results however, show that the minimal solvent effect on the reaction free energy is accompanied by a significant reorganization of the solvent. © 2011 American Institute of Physics.

Localized oxide spots were grown at the grain boundaries of a technically relevant 30at.% Nb-Ti β-type titanium alloy to study the local electrochemical response. The grain boundaries selected were combinations of grains having different orientations and grain boundary angle. Crystallographic information of the grains and boundary angles were revealed by electron back scattering diffraction (EBSD) technique. Cyclic voltammetry is the electrochemical technique used to grow the oxides starting from 0V and increasing the potential in steps of 1V till 8V at a scan rate of 100mVs -1 in an acetate buffer of pH 6.0. Electrochemical impedance spectroscopy was used to investigate the electrical properties of the oxide/electrolyte interface in the frequency range between 100kHz and 100mHz. Important oxide parameters such as formation factor and dielectric number were determined from these measurements. Significant differences were observed for different grain boundaries. The semiconducting properties of the oxides at the grain boundaries were assessed by using Mott-Schottky analysis on a potentiostatically grown oxide. All the oxides showed n-type semiconducting properties where the donor concentration varies with the grain boundaries mentioned above. A flat band potential -0.25 ±0.02V versus standard hydrogen electrode is more or less the same for all the boundaries studied. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ag/ZnO nanocomposites were developed by a plasma-assisted approach. The adopted strategy exploits the advantages of Plasma Enhanced-Chemical Vapor Deposition (PE-CVD) for the growth of columnar ZnO arrays on Si(100) and Al 2O3 substrates, in synergy with the infiltration power of the Radio Frequency (RF)-sputtering technique for the subsequent dispersion of different amounts of Ag nanoparticles (NPs). The resulting composites, both as-prepared and after annealing in air, were thoroughly characterized with particular attention on their morphological organization, structure and composition. For the first time, the above systems have been used as catalysts in the production of hydrogen by photo-reforming of alcoholic solutions, yielding a stable H2 evolution even by the sole use of simulated solar radiation. In addition, Ag/ZnO nanocomposites presented an excellent response in the gas-phase detection of H2, opening attractive perspectives for advanced technological applications. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

The local surface chemistry of a low-Ni austenitic stainless steel AISI type 304 used for tensile testing in hydrogen atmosphere is characterized by secondary ion mass spectrometry (SIMS). A chemical map on cylindrical austenitic stainless steel samples can be obtained even after a tensile test. In an effort to obtain the proper chemical element distribution on the samples, the influence of contamination and sample orientation is discussed. An iron oxide on top of a chromium oxide layer is present and Si segregation at grain boundaries is detected. Oxides are judged to reduce the initial hydrogen attack but to be of minor importance for crack propagation during the embrittlement process. © 2011 Elsevier B.V. All rights reserved.

Plasma processing represents an attractive and versatile option for the fabrication of low-dimensional nanomaterials, whose chemical and physical properties can be conveniently tailored for the development of advanced technologies. In particular, Plasma Enhanced-Chemical Vapor Deposition (PE-CVD) is an appealing route to multi-functional oxide nanoarchitectures under relatively mild conditions, owing to the unique features and activation mechanisms of non-equilibrium plasmas. In this context, the potential of plasma-assisted fabrication in advanced nanosystem development is discussed. After a brief introduction on the basic categories of plasma approaches, the perspectives of application to CVD processes are commented, reporting on the growth and characterization of Co 3O 4 nanomaterials as a case study. Besides examining the interrelations between the material properties and the synthesis conditions, special focus is given to their emerging applications as catalysts for photo-assisted hydrogen production and solid state gas sensors. Copyright © 2011 American Scientific Publishers All rights reserved.

An in-depth understanding of the fundamental structure of catalysts during operation is indispensable for tailoring future efficient and selective catalysts. We report the evolution of the structure and oxidation state of ZrO2-supported Pd nanocatalysts (∼5 nm) during the in situ reduction of NO with H2 using X-ray absorption fine-structure spectroscopy and X-ray photoelectron spectroscopy. Prior to the onset of the reaction (≤120 °C), a NO-induced redispersion of our initial metallic Pd nanoparticles over the ZrO2 support was observed, and Pd δ+ species were detected. This process parallels the high production of N2O observed at the onset of the reaction (>120 °C), while at higher temperatures (≥150 °C) the selectivity shifts mainly toward N2 (∼80%). Concomitant with the onset of N 2 production, the Pd atoms aggregate again into large (6.5 nm) metallic Pd nanoparticles, which were found to constitute the active phase for the H2-reduction of NO. Throughout the entire reaction cycle, the formation and stabilization of PdOx was not detected. Our results highlight the importance of in situ reactivity studies to unravel the microscopic processes governing catalytic reactivity. © 2011 American Chemical Society.

Future energy systems, which will rely on substantially higher contributions from regenerative supply pathways and which will be increasingly less dependent on fossil energy resources, will require high energy density storage compounds as strategic reserves and for seasonal storage. Hydrocarbons, such as oil and natural gas, are currently serving this purpose. These will also be options in future systems, but in that case, these compounds would have to be synthesized using some other form of energy. Thus, with decreasing importance of fossil resources, other storage compounds also seem to be viable, the most prominent ones under discussion, in addition to the ones mentioned, being hydrogen, methanol, and ethanol. In this contribution, the different storage compounds will be discussed, and their merits and drawbacks for large scale implementation will be compared. The intensified use of renewable sources in future energy systems implies the demand for high density storage compounds. Hydrogen, methane, liquid hydrocarbons, methanol, and ethanol are potential candidates for that purpose. The different storage compounds are discussed and their advantages and drawbacks are compared. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mg2Ni-TiFe and Mg2Ni-TiNi nanocomposites were prepared by milling for a short time of two preliminary milled to a nanocrystalline state hydrogen absorbing phases, Mg2Ni and TiFe or Mg2Ni and TiNi. The milling results in a sufficient density of contacts between the fine powder particles with different composition. The presence of a large amount of such inter-particles contacts leads to lowering of the initial temperature of the composites gas phase hydriding, as in the same time the temperature range of hydriding is enlarged, compared to the composites components. On the grounds of the proved low temperature hydriding (≤200 °C) of the nanocomposites, taking place with appropriate kinetics, the possibility for improved electrochemical hydriding was checked, exploiting the idea for charging Mg2Ni particles through the contacts with TiFe/TiNi. In this way we are supposed to achieve more complete electrochemical hydriding of the Mg2Ni particles, which are usually only superficially hydrogenated at room temperature, mainly due to the low diffusion coefficient of hydrogen in the Mg2Ni crystal lattice and corrosion processes in strong alkaline solutions. The achieved discharge capacity for the Mg2Ni-TiFe composite is essentially higher compared to that of the mechanical mixture of the two composite's components. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights.

The effect of hydrostatic strain and of interstitial hydrogen on the elastic properties of α-iron is investigated using ab initio density-functional theory calculations. We find that the cubic elastic constants and the polycrystalline elastic moduli to a good approximation decrease linearly with increasing hydrogen concentration. This net strength reduction can be partitioned into a strengthening electronic effect which is overcome by a softening volumetric effect. The calculated hydrogen-dependent elastic constants are used to determine the polycrystalline elastic moduli and anisotropic shear moduli. For the key slip planes in α-iron, [11̄0] and [112̄], we find a shear modulus reduction of approximately 1.6% per at.% H. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

p-Type Co3O4 nanostructured films are synthesized by a plasma-assisted process and tested in the photocatalytic production of H 2 from water/ethanol solutions under both near-UV and solar irradiation. It is demonstrated that the introduction of fluorine into p-type Co3O4 results in a remarkable performance improvement with respect to the corresponding undoped oxide, highlighting F-doped Co 3O4 films as highly promising systems for hydrogen generation. Notably, the obtained yields were among the best ever reported for similar semiconductor-based photocatalytic processes. © 2011 American Chemical Society.

The efficient electron transfer between redox enzymes and electrode surfaces can be obtained by wiring redox enzymes using, for instance, polymer-bound redox relays as has been demonstrated as a basis for the design of amperometric biosensors, logic gates or sensor arrays and more general as a central aspect of "bioelectrochemistry". Related devices allow exploiting the unique catalytic properties of enzymes, among which photosynthetic enzymes are especially attractive due to the possibility to trigger the redox reactions upon irradiation with light. Photocatalytic properties such as the light-driven water splitting by photosystem 2 make them unique candidates for the development of semiartificial devices which convert light energy into stable chemical products, like hydrogen. This review summarizes recent concepts for the integration of photosystem 1 and photosystem 2 into bioelectrochemical devices with special focus on strategies for the design of electron transfer pathways between redox enzymes and conductive supports. © 2011 The Royal Society of Chemistry.

The adsorption of carbon monoxide on an either unpromoted or potassium-promoted bulk iron catalyst was investigated at 303 K and 613 K by means of pulse chemisorption, adsorption calorimetry, temperature-programmed desorption and temperature-programmed surface reaction in hydrogen. CO was found to adsorb mainly molecularly in the absence of H 2 at 303 K, whereas the presence of H 2 induced CO dissociation at higher temperatures leading to the formation of CH 4 and H 2O. The hydrogenation of atomic oxygen chemisorbed on metallic iron was found to occur faster than the hydrogenation of atomically adsorbed carbon. At 613 K CO adsorption occurred only dissociatively followed by recombinative CO 2 formation according to C ads + 2O ads → CO 2(g). The presence of the potassium promoter on the catalyst surface led to an increasing strength of the Fe-C bond both at 303 K and 613 K: the initial differential heat of molecular CO adsorption on the pure iron catalyst at 303 K amounted to 102 kJ mol -1, whereas it increased to 110 kJ mol -1 on the potassium-promoted sample, and the initial differential heat of dissociative CO adsorption on the unpromoted iron catalyst at 613 K amounted to 165 kJ mol -1, which increased to 225 kJ mol -1 in the presence of potassium. The calorimetric CO adsorption experiments also reveal a change of the energetic distribution of the CO adsorption sites present on the catalyst surface induced by the potassium promoter, which was found to block a fraction of the CO adsorption sites. © the Owner Societies 2011.

Nanostructured MgH2/0.1TiH2 composite was synthesized directly from Mg and Ti metal by ball milling under an initial hydrogen pressure of 30 MPa. The synthesized composite shows interesting hydrogen storage properties. The desorption temperature is more than 100 °C lower compared to commercial MgH2 from TG-DSC measurements. After desorption, the composite sample absorbs hydrogen at 100 °C to a capacity of 4 mass% in 4 h and may even absorb hydrogen at 40 °C. The improved properties are due to the catalyst and nanostructure introduced during high pressure ball milling. From the PCI results at 269, 280, 289 and 301 °C, the enthalpy change and entropy change during the desorption can be determined according to the van't Hoff equation. The values for the MgH2/0.1TiH2 nano-composite system are 77.4 kJ mol-1 H2 and 137.5 J K-1 mol-1 H2, respectively. These values are in agreement with those obtained for a commercial MgH2 system measured under the same conditions. Nanostructure and catalyst may greatly improve the kinetics, but do not change the thermodynamics of the materials. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

The effect of B on the fracture behavior of Ni3Fe alloys (24 and 26 at.% Fe) was studied after cathodic charging with hydrogen. In contrast to its disordered state, ordered Ni3Fe underwent brittle intergranular fracture at room temperature. Boron addition changed its fracture mode to predominantly ductile transgranular. The grain boundary chemistry of ordered Ni3Fe was analyzed by Auger electron spectroscopy. Boron was found to segregate to the grain boundaries of both Ni-24Fe and Ni-26Fe and reduce the hydrogen-induced embrittlement of these alloys in the ordered state. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Formic acid (HCOOH) has great potential as an in situ source of hydrogen for fuel cells, because it offers high energy density, is non-toxic and can be safely handled in aqueous solution. So far, there has been a lack of solid catalysts that are sufficiently active and/or selective for hydrogen production from formic acid at room temperature. Here, we report that Ag nanoparticles coated with a thin layer of Pd atoms can significantly enhance the production of H 2 from formic acid at ambient temperature. Atom probe tomography confirmed that the nanoparticles have a core-shell configuration, with the shell containing between 1 and 10 layers of Pd atoms. The Pd shell contains terrace sites and is electronically promoted by the Ag core, leading to significantly enhanced catalytic properties. Our nanocatalysts could be used in the development of micro polymer electrolyte membrane fuel cells for portable devices and could also be applied in the promotion of other catalytic reactions under mild conditions. © 2011 Macmillan Publishers. All rights reserved.

The chemical composition of an AISI type 304 austenitic stainless was systematically modified in order to evaluate the influence of the elements Mo, Ni, Si, S, Cr and Mn on the material's susceptibility to hydrogen environment embrittlement (HEE). Mechanical properties were evaluated by tensile testing at room temperature in air at ambient pressure and in a 40 MPa hydrogen gas atmosphere. For every chemical composition, the corresponding austenite stability was evaluated by magnetic response measurements and thermodynamic calculations based on the Calphad method. Tensile test results show that yield and tensile strength are negligibly affected by the presence of hydrogen, whereas measurements of elongation to rupture and reduction of area indicate an increasing ductility loss with decreasing austenite stability. Concerning modifications of alloy composition, an increase in Si, Mn and Cr content showed a significant improvement of material's ductility compared to other alloying elements. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Uniform amorphous carbon film is deposited on the inner surface of quartz tubes having an inner diameter of 6 mm and an outer diameter of 8 mm. A pulsed filamentary plasma source is used for the deposition. Long plasma filaments (~140 mm) are generated inside the tube in argon with methane admixture. FTIR-ATR, XRD, scanning electron microscope, laser scanning microscope and XPS analyses give the conclusion that deposited film is amorphous composed of non-hydrogenated sp2 carbon and hydrogenated sp3 carbon. Plasma is characterized using optical emission spectroscopy, voltage-current measurement, microphotography and numerical simulation. On the basis of observed plasma parameters, the kinetics of the film deposition process is discussed. © 2011 IOP Publishing Ltd.

To address the upcoming austenitic stainless steel market for automotive applications involving hydrogen technology, a novel lean - alloyed material was developed and characterized. It comprises lower contents of nickel and molybdenum compared to existing steels for high - pressure hydrogen uses, for instance 1.4435 (AISI 316L). Alloying with manganese and carbon ensures a sufficient stability of the austenite at 8. wt.% of nickel while silicon is added to improve resistance against embrittlement by dissolved hydrogen. Investigations were performed by tensile testing in air and 400. bar hydrogen at 25 °C, respectively. In comparison to a standard 1.4307 (AISI 304L) material, a significant improvement of ductility was found. The materials concept is presented in general and discussed with regard to austenite stability and microstructure. © 2011 Elsevier B.V.

Nanocrystalline Ti-catalyzed MgH2 can be prepared by a homogeneously catalyzed synthesis method. Comprehensive characterization of this sample and measurements of hydrogen storage properties are discussed and compared to a commercial MgH2 sample. The catalyzed MgH2 nanocrystalline sample consists of two MgH2 phases-a tetrahedral β-MgH2 phase and an orthorhombic high-pressure modification γ-MgH2. Transmission electron microscopy was used for the observation of the morphology of the samples and to confirm the nanostructure. N2 adsorption measurement shows a BET surface area of 108m 2g-1 of the nanostructured material. This sample exhibits a hydrogen desorption temperature more than 130 °C lower compared to commercial MgH2. After desorption, the catalyzed nanocrystalline sample absorbs hydrogen 40 times faster than commercial MgH2 at 300 °C. Both the Ti catalyst and the nanocrystalline structure with correspondingly high surface area are thought to play important roles in the improvement of hydrogen storage properties. The desorption enthalpy and entropy values of the catalyzed MgH2 nanocrystalline sample are 77.7kJmol-1H2 and 138.3JK-1mol -1H2, respectively. Thermodynamic properties do not change with the nanostructure. © 2011 IOP Publishing Ltd.

Hydrogen-assisted fracture of AISI type 304 steel has been evaluated with a special focus on the strain-induced martensite that is produced below the specimen surface during standard turning operation. Two different surface conditions were investigated: one containing martensite, resulting from the machining process, and a martensite-free state which is obtained after a proper heat treatment. Additionally, chemical composition and thickness of oxide layers, occurring in both studied cases, were analyzed by secondary ion mass spectrometry. These two different conditions were tested at room temperature in air (ambient pressure) and in hydrogen gas (40 MPa) atmosphere, respectively. Experimental results reveal a detrimental effect of machining-induced martensite on AISI type 304 steel performance in hydrogen, leading to major differences in relative reduction of area (RRA) between the as-machined and the heat-treated state for the same material. In this context, an operating mechanism based on hydrogen diffusion is discussed. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Scanning electrochemical microscopy in the redox competition mode (RC-SECM) is proposed as an useful technique for local investigation of the electrocatalytic activity of different catalysts towards the oxygen reduction reaction (ORR) with simultaneous detection of the produced undesirable intermediate hydrogen peroxide. We have used cobalt porphyrin dispersed in a multiwalled carbon nanotubes (MWCNTs) matrix as a model electrocatalyst for the predominant two-electron reduction of oxygen to hydrogen peroxide. Furthermore, Prussian Blue or horseradish peroxidase were used as catalysts for the further reduction of hydrogen peroxide to water. The properties of each component of the film were examined along with their potential interactions with the other components. As a result an efficient electrocatalyst for oxygen reduction at physiological pH could be obtained. ©The Electrochemical Society.

A hydrogen storage tank based on the metal hydride sodium alanate is coupled with a high temperature PEM fuel cell (HT-PEM). The waste heat of the fuel cell is used for desorbing hydrogen from the storage tank that in return feeds the fuel cell. ZBT has developed the HT-PEM fuel cell, Max-Planck-Institut für Kohlenforschung the sodium alanate, and IUTA the hydrogen storage tank. During the experiments of the system the fuel cell was operated by load cycling from 165 up to 240 W. Approximately 60 g of hydrogen were delivered from the tank, which was charged with 2676.8 g of sodium alanate doped with 4 mol.% of TiCl 3. This amount of hydrogen was desorbed in 3 h and generated a cumulated electrical energy of 660 Wh. In the first cycle 81.5 g of hydrogen were supplied during 3.69 h to the HT-PEM fuel cell, which was operated nearly constant at 260 W. In the latter case the cumulated electrical energy was 941 Wh. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Self-assembled quantum dots (QDs) are prominent candidates for solid-state quantum information processing. For these systems, great progress has been made in addressing spin states by optical means. In this study, we introduce an all-electrical measurement technique to prepare and detect non-equilibrium many-particle spin states in an ensemble of self-assembled QDs at liquid helium temperature. The excitation spectra of the one- (QD hydrogen), two- (QD helium) and three- (QD lithium) electron configuration are shown and compared with calculations using the exact diagonalization method. An exchange splitting of 10 meV between the excited triplet and singlet spin states is observed in the QD helium spectrum. These experiments are a starting point for an all-electrical control of electron spin states in self-assembled QDs above liquid helium temperature. © 2011 Macmillan Publishers Limited. All rights reserved.

Background: In recent years, plasma treatment of medical devices and implant materials has gained more and more acceptance. Inactivation of microorganisms by exposure to ultraviolet (UV) radiation produced by plasma discharges and sterilization of medical implants and instruments is one possible application of this technique. The aim of this study was to evaluate the effectiveness of this sterilization technique on silicone implant material. Methods: Bacillus atrophaeus spores (106 colony-forming units [CFUs]) were sprayed on the surfaces of 12 silicone implant material samples. Four plasma sets with different gas mixtures (argon [Ar], argon-oxygen [Ar:O 2], argon-hydrogen [Ar:H2] and argon-nitrogen [Ar:N 2]) were tested for their antimicrobial properties. Post-sterilization mechanical testing of the implant material was performed in order to evaluate possible plasma-induced structural damage. Results: The inductively coupled low-pressure plasma technique can achieve fast and efficient sterilization of silicone implant material without adverse materials effects. All four gas mixtures led to a significant spore reduction, and no structural damage to the implant material could be observed.

Electrochemically-assisted deposition of sol-gel materials can be locally confined at Pt nanoparticles. Pt nanoparticles have been locally deposited on glassy carbon surfaces by pulse electrodeposition using a droplet cell. Upon applying a potential for electrochemically-assisted deposition, the formed sol-gel film mirrors the region of the glassy carbon surface previously modified with Pt nanoparticles. © 2011 Elsevier B.V. All rights reserved.

The ball milling conditions in the preparation of rare earth aluminum hydrides from NaAlH4 and rare earth chlorides have a significant influence on product formation. Defined milling times and appropriate rotational speeds are required to obtain the desired products. It has been shown that starting directly from Na3AlH6 does not lead to the formation of REAlH6. Starting from rare earth iodides instead of chlorides allows dissolution of the alkali metal iodide formed and, therewith, the preparation of salt-free rare earth aluminum hydrides. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Precipitation of zinc sulfide particles is a very rapid process, and monitoring of the particle growth is experimentally very demanding. Applying a liquid jet flow cell, we were able to follow zinc sulfide particle formation on time scales down to 10 -5 s. The flow cell was designed in such a way that data acquisition on the microsecond time scale was possible under steady-state conditions along a liquid jet (tubular reactor concept), allowing SAXS data accumulation over a time scale of minutes. We were able to monitor the growth of zinc sulfide particles and found experimental evidence for very rapid particle aggregation processes within the liquid jet. Under the experimental conditions the particle growth is controlled by mass transfer: i.e., the diffusion of the hydrogen sulfide into the liquid jet. © 2010 American Chemical Society.

Purpose: The effect of cold low-pressure plasma treatment on neovascularization of a dermis substitute was evaluated in a mouse model. Material and methods: Collagen-elastin matrices (Matriderm®) were used as scaffolds. Low-pressure argon/hydrogene plasma-treated scaffolds were transplanted into the dorsal skinfold chambers of balb/c mice (group 1, n = 10). Untreated scaffolds served as controls (group 2, n = 10). Intravital fluorescence microscopy was performed within the border zone of the scaffolds on days 1, 5 and 10. Functional vessel density (FVD), vessel diameter, intervascular distance, microvascular permeability, and leukocyte-endothelium interaction were analyzed. Results: An increase of FVD associated with a reduction of the intervascular distance was observed. Statistical analysis revealed that the functional vessel density in the border zone of the scaffolds was significantly enhanced in the plasma-treated group compared to controls. For group 1, an increase of FVD from 282 ± 8 cm/cm2 on days 5 to 315 ± 8 cm/cm2 on day 10 was observed. Whereas values of 254 ± 7 cm/cm2 on day 5 and 275 ± 13 cm/cm2 on day 10 have resulted in group 2 (mean ± S.E.M., Student's t-test, p < 0.05). Conclusion: The surface treatment by cold low-pressure plasma intensifies the angiogenesis and accelerates the neovascularization of collagen-elastin matrix. © 2010 Elsevier Ltd and ISBI. All rights reserved.

Chemical trends for the solubility and diffusivity of hydrogen in austenitic high Mn steels have been studied employing density-functional theory. Considering the dilute limit of hydrogen, we observe strong volumetric effects of substitutional Mn and interstitial carbon on the energetics of a hydrogen atom within the lattice. This volume dependence yields a significant increase both in the solubility and the mobility of the H impurity when comparing Fe1-x Mnx Cy with pure Fe. By means of kinetic Monte Carlo calculations, we also show that H impurities can use Mn percolation chains as efficient diffusion channels. These trends may explain why Mn-rich steels are often observed to be more prone to hydrogen embrittlement than conventional austenitic steels. © 2010 The American Physical Society.

Using iron oxide as catalyst, glycerol can be converted to allyl alcohol through a dehydration and consecutive hydrogen transfer. © 2010 The Royal Society of Chemistry.

Structural and surface properties of carbon-containing mesoporous MoS 2 and of a reference MoS2 were studied with various techniques including XRD, elemental analysis, TEM, XPS, EXAFS, nitrogen physisorption, oxygen chemisorption (OCS), determination of exchangeable surface hydrogen, and kinetic study of test reactions like ethene hydrogenation and H2/D2 exchange. The study was made before and after use of these catalysts in the hydrodesulfurization of dibenzothiophene. The microstructure of carbon-stabilized MoS2 is characterized by nanoslabs of 2 nm average stacking height embedded in an amorphous matrix with a very broad pore-size distribution. Thermal stress induced a collapse of the microporous structure leading to the formation of mainly mesopores. The carbon is well-distributed over the bulk, without any signature of carbide species detected neither in XPS nor in EXAFS measurements. The activity patterns of both materials (related to the OCS capacity) were similar despite the differing sulfur content, with the carbon-stabilized MoS2 being more sulfur deficient. This suggests that the catalytic properties of the latter material were caused by near-stoichiometric MoS2 apparently present in the nanoslabs, whereas the sulfur vacancies in the sulfur-deficient amorphous phase were blocked by strongly adsorbed carbon residues. Interestingly, the HDS reaction did not cause significant changes of the properties of the carbon-stabilized MoS2. Conversely, the reference MoS2 was strongly activated, in particular with respect to ethene hydrogenation, which can be explained by a pronounced sulfur loss during the HDS reaction, without significant site blockage by the coke deposited. © 2010 Elsevier B.V. All rights reserved.

The use of first-row transition metals for the catalytic reduction of carbonyl functionalities has become increasingly important in homogeneous catalysis. This Perspective examines the mechanistic aspects of these reduction reactions, with a focus on various interactions between metal complexes and substrates. Four different types of catalytic pathways, namely catalysis with dihydride (or dihydrogen) complexes, catalysis with monohydride complexes, metal-ligand bifunctional catalysis, and catalysis involving ionic mechanisms, are discussed with recent examples highlighted. © 2010 The Royal Society of Chemistry.

The interaction of vacancies and hydrogen in an fcc iron bulk crystal was studied combining thermodynamic concepts with ab initio calculations and considering various magnetic structures. We show that up to six H atoms can be trapped by a monovacancy. All of the studied point defects (single vacancy, H in interstitial positions, and H-vacancy complexes) cause an anisotropic elastic field in antiferromagnetic fcc iron and significantly change the local and total magnetization of the system. The proposed thermodynamical model allows the determination of the equilibrium vacancy concentration and the concentration of dissolved hydrogen for a given temperature and H chemical potential in the reservoir. For H-rich conditions a dramatic increase in the vacancy concentration in the crystal is found. © 2010 The American Physical Society.

Carbon nanotube (CNT) supported sulfided Rh catalysts were prepared applying three different routes: deposition-precipitation (DP), grafting of colloidal Rh nanoparticles, and polythiophene-assisted synthesis. The catalysts (1.4-1.8 wt%) prepared by DP were synthesized on CNTs from RhCl3 using hydrogen peroxide and subsequent exposure to on-line generated H 2S followed by heat treatment. The Rh particles were found to be highly dispersed on the CNT surface. Alternatively, RhSx/Rh nanoparticles with four different loadings (4.3-21.9 wt%) grafted on carbon nanotubes were prepared through a functionalization of CNTs with short chain thiols and subsequent binding of colloidal Rh nanoparticles onto the thiolated CNTs. All steps of the synthesis were monitored by XPS. Finally, polythiophene/CNT composites were prepared and employed in the preparation of Rh17S15/Rh nanoparticles supported on CNTs. The CNTs with the highest polythiophene loading yielded the highest amount of Rh 17S15 after Rh deposition and thermal treatment. The activity and stability of the prepared catalysts were studied towards the oxygen reduction reaction. © 2010 Elsevier B.V. All rights reserved.

The formation energy and solubility of hydrogen in magnesium nitride bulk (antibixbyite Mg3 N2) have been studied employing density functional theory in the generalized gradient approximation. The effect of doping and the presence of native defects and complex formation have been taken into account. Our results show that magnesium nitride is a nearly defect-free insulator with insignificant hydrogen-storage capacity. Based on this insight we derive a model that highlights the role of the formation and presence of the parasitic Mg3 N2 inclusions in the activation of p -doped GaN in optoelectronic devices. © 2010 The American Physical Society.

Exposing ZnO nanoparticles to atomic and molecular hydrogen at room temperature decreases the transmission coefficient, which demonstrates that diffusion of hydrogen atoms to subsurface and bulk ZnO sites already occurs at these fairly low temperatures (see figure). The interstitial hydrogen atoms act as n-type shallow donors, which increase the density of electrons in the conduction band. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The structure, size, and shape of γ-Al2O 3-supported Pt nanoparticles (NPs) synthesized by inverse micelle encapsulation have been resolved via a synergistic combination of imaging and spectroscopic tools. It is shown that this synthesis method leads to 3D NP shapes even for subnanometer clusters, in contrast to the raft-like structures obtained for the same systems via traditional deposition-precipitation methods. Furthermore, a high degree of atomic ordering is observed for the micellar NPs in H2 atmosphere at all sizes studied, possibly due to H-induced surface reconstruction in these high surface area clusters. Our findings demonstrate that the influence of NP/support interactions on NP structure can be diminished in favor of NP/adsorbate interactions when NP catalysts are prepared by micelle encapsulation methods. © 2010 American Chemical Society.

Combining density-functional-theory calculations and atomistic thermodynamics we study hydrogen adsorption on the Zn-terminated polar ZnO(0001) surface. We extend the concept of equilibrium surface phase diagrams to include kinetically stabilized surface reconstructions by constructing metastable phase diagrams and going beyond the thermodynamic limit. Under these conditions we find a monolayer H coverage to be extremely favorable on triangular-shaped reconstructions due to a simultaneous protonation of step-edge oxygen atoms and surface terminating Zn atoms. Experimental situations, which realize hydrogen chemical potentials outside the stability range of the H2 molecule are discussed. © 2010 The American Physical Society.

Carbon fiber nanoelectrodes with nanometer radii tip curvatures were fabricated using a shearforce-based constant-distance scanning electrochemical microscope and electrochemically induced polymer deposition. A simple DC etching procedure in alkaline solution provided conically sharpened single carbon fibers with well-formed nanocones at their bottom. Coating the stems but not the end of the tips of the tapered structures with anodic electrodeposition paint was the strategy for limiting the bare carbon to the foremost end and restricting a feasible voltammetry current response to exactly this section. The electrodeposition of the polymer was prevented at the foremost end of the tip using a shearforce-based tip-to-sample distance control that allowed approaching the etched tips carefully in just touching distance to a film of a silicone elastomer. Analysis of the steady-state cyclic voltammograms in presence of a reversible redox compound revealed effective radii for the obtained needle-type carbon-fiber nanoelectrodes down to as small as 46 nm. The method offers an alternative pathway toward the fabrication of highly miniaturized carbon electrodes. © 2010 American Chemical Society.

In this work, 1D ZnO nano-assemblies were prepared on Al2O 3 substrates by plasma enhanced-chemical vapor deposition (PE-CVD), and characterized in their morphology and chemical composition by field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDXS) and X-ray photoelectron spectroscopy (XPS). For the first time, the sensing performances of PE-CVD ZnO nanosystems were tested in the detection of toxic/combustible gases (CO, H2 and CH4), revealing very good responses already at moderate working temperatures. In particular, carbon monoxide and hydrogen detection was possible already at 100 °C, whereas methane sensing required a minimum temperature of 200 °C. The performances of the present ZnO nanosystems, that make them attractive candidates for technological applications, are presented and discussed in terms of their unique and controllable morphological organization. © 2010 Elsevier B.V. All rights reserved.

The production of fermentable sugars from cellulose in almost quantitative yield is accelerated. Starting from cello-oligomers obtained by acid hydrolysis of cellulose in an ionic liquid, the catalytic approach described herein, integrating acid and enzymatic catalysis, quantitatively converts cellulose to fermentable sugars (glucose and cellobiose) within only a few hours. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The design of advanced porous materials is crucial for the development of new energy storage systems for mobile applications. In the following a new class of highly porous carbon structures is applied in gas storage. Ordered mesoporous carbide derived carbons (OM-CDC) were synthesized by chlorination of mesostructured silicon carbide ceramics (OM-SiC). Resulting OM-CDC structures were characterized by nitrogen physisorption methods and small angle X-ray scattering demonstrating high specific surface areas and bimodal pore size distributions by varying the synthesis and chlorination conditions. The adsorption properties could be further enhanced by reductive hydrogen treatment. Storage capacities for mobile applications dependant on the synthesis conditions were investigated in high pressure hydrogen and methane adsorption with extraordinary high uptakes compared to micro- and mesoporous reference materials. In addition, the adsorption kinetics are studied in dynamic n-butane adsorption. © 2010 Elsevier Ltd. All rights reserved.

Simple mechanochemical procedures can be used for the solid-state preparation of stable complex aluminium hydrides as hydrogen storage materials. For the synthesis of unstable complex hydrides, cryomilling at temperatures at which product decomposition does not take place under milling conditions appears to be a viable method. To probe the potential of cryomilling for the synthesis of complex aluminium hydrides, the reactions of different alkaline hydrides with AlH3 were tested under these conditions. © 2009 Acta Materialia Inc.

The design of polymers carrying suitable ligands for coordinating Os complexes in ligand exchange reactions against labile chloro ligands is a strategy for the synthesis of redox polymers with bound Os centers which exhibit a wide variation in their redox potential. This strategy is applied to polymers with an additional variation of the properties of the polymer backbone with respect to pH-dependent solubility, monomer composition, hydrophilicity etc. A library of Os-complex-modified electrodeposition polymers was synthesized and initially tested with respect to their electron-transfer ability in combination with enzymes such as glucose oxidase, cellobiose dehydrogenase, and PQQ-dependent glucose dehydrogenase entrapped during the pH-induced deposition process. The different polymer-bound Os complexes in a library containing 50 different redox polymers allowed the statistical evaluation of the impact of an individual ligand to the overall redox potential of an Os complex. Using a simple linear regression algorithm prediction of the redox potential of Os complexes becomes feasible. Thus, a redox polymer can now be designed to optimally interact in electron-transfer reactions with a selected enzyme. © 2010 Springer-Verlag.

In this contribution we review our recently developed method for the calculation of acidity constants from density functional theory based molecular dynamics simulations. The method is based on a half reaction scheme in which protons are formally transferred from solution to the gas phase. The corresponding deprotonation free energies are computed from the vertical energy gaps for insertion or removal of protons. Combined to full proton transfer reactions, the deprotonation energies can be used to estimate relative acidity constants and also the Brønsted pKa when the deprotonation free energy of a hydronium ion is used as a reference. We verified the method by investigating a series of organic and inorganic acids and bases spanning a wide range of pKa values (20 units). The thermochemical corrections for the biasing potentials assisting and directing the insertion are discussed in some detail. © 2010 IOP Publishing Ltd.

The effects of grain size and of crack-tip blunting radius on the fracture toughness of tungsten polycrystals are studied by using a combined dislocation dynamics/cohesive zone model (CZM). Two-dimensional dislocation dynamics are employed to analyze crack-tip plasticity and crack propagation is characterized by a CZM. The geometry of the crack and the corresponding boundary conditions are described by means of a boundary element method with dislocation dipoles as fundamental solution. Grain boundaries are introduced as obstacles for dislocation motion. Numerical experiments reveal that the fracture toughness decreases with grain size, because grain boundaries confine the plastic zone. This effect is particularly pronounced at small loading rates, where the unconfined plastic zone is large. Our results also show that fracture toughness scales with the tip radius as the stress concentration at the crack tip is reduced and the plastic zone is enlarged. © 2009 Acta Materialia Inc.

Two genetic algorithms for the single- and multiobjective design of combinatorial experiments were applied to the optimization of a solid catalyst system active in the selective catalytic oxidation of propane to propylene. The two different optimization strategies, namely, the single objective optimization of the yield and the multiobjective optimization of the conversion and selectivity were implemented and compared. It was observed that the multiobjective approach optimized the yield in a similar way compared to the single objective approach. With respect to the selectivity, however, the multiobjective outperformed the single objective approach. It was also found that by applying the multiobjective optimization more interesting possible combinations were discovered. © 2009 American Chemical Society.

A membrane-free biofuel cell (BFC) is reported based on enzymes wired to graphite electrodes by means of Os-complex modified redox polymers. For the anode cellobiose dehydrogenase (CDH) is used as a biocatalyst whereas for the cathode a laccase was applied. This laccase is a high-potential laccase and hence able to reduce O2 to H2O at a formal potential higher than +500 mV versus Ag/AgCl. In order to establish efficient electrochemical contact between the enzymes and graphite electrodes electrodeposition polymers containing Os-complex with specifically designed monomer compositions and formal potentials of the coordinatively bound Os-complex were synthesised and used to wire the enzymes to the electrodes. The newly designed CDH/Os-redox polymer anode was characterised at different pH values and optimised with respect to the nature of the polymer and the enzyme-to-polymer ratio. The resulting BFC was evaluated running on β-lactose as a fuel and air/O2as an oxidising agent. The power output, the maximum current density and the electromotor force (Eemf) were found to be affected by the pH value, resulting in a maximum power output of 1.9 μWcm-2 reached at pH 4.3, a maximum current density of about 13 μAcm-2 at pH 3.5, and the highest Eemf approaching 600 mV at pH 4.0. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA.

The so-called "one-step direct synthesis method" - simultaneous ball-milling (b.m.) of NaH-Al powder doping agent mixtures under H2 pressure - turned out to be a simple way for the preparation of metal-doped sodium alanate hydrogen storage materials, leading to solids with high storage capacity and excellent kinetics. The method has been published until now only for TiCl3 as a doping agent. In combination with ScCl3 or CeCl3 as doping agents, the one-step direct synthesis method delivers materials with hydrogen storage properties which come close to those required by the car industry for hydrogen supply of PEM fuel cells. With respect to the kinetics of the chemical reaction, hydrogenation rates corresponding to 3-5 min time for refuelling of a hydrogen tank can be realized, although removal of the resulting hydrogenation heat in such a short time posses a severe engineering problem. Release of all stored hydrogen in a time compatible with handling of a car is possible without additional heating devices, if instead of the current fuel cells, advanced designs on the basis of polybenzimidazole membranes are used. These fuel cells work at temperatures of 150-200 °C, so that their waste heat temperature level is sufficiently high for desorption of hydrogen from both dehydrogenation steps of the NaAlH4 system. Additionally, it has been reported that using mischmetal with 42 at.% of Ce as a dopant for NaAlH4, at 150 °C, ∼5 wt.% of hydrogen can be desorbed in ∼3 h. Moreover, in a 95 cycles de- and re-hydrogenation test the present Ce-doped NaAlH4 storage material showed stable storage properties. © 2008 Elsevier B.V. All rights reserved.

Hydrogen is a promising energy carrier in future energy systems. However, storage of hydrogen is a substantial challenge, especially for applications in vehicles with fuel cells that use proton-exchange membranes (PEMs). Different methods for hydrogen storage are discussed, including high-pressure and cryogenic-liquid storage, adsorptive storage on high-surface-area adsorbents, chemical storage in metal hydrides and complex hydrides, and storage in boranes. For the latter chemical solutions, reversible options and hydrolytic release of hydrogen with off-board regeneration are both possible. Reforming of liquid hydrogen-containing compounds is also a possible means of hydrogen generation. The advantages and disadvantages of the different systems are compared. © 2009 Wiley-VCH Verlag GmbH & Co. KCaA.

Classical hydrogenation catalysts usually give high activities at mild conditions, but often low selectivities. Hydrogenations with complex hydrides like NaBH4 or LiAlH4 are rather selective, but these hydrides must be employed in stoichiometric amounts. We have investigated the catalytic hydrogenation of tolane (diphenylacetylene) with gas phase hydrogen over Ti- and Ce-doped NaAlH4 and Na3AlH6. These hydrides are reversible; i.e. can be rehydrogenated with pressurized hydrogen after the dehydrogenation, so they can be used in catalytic amounts for the hydrogenation of unsaturated hydrocarbons. We propose a mechanism involving the cycling of the hydride between hydrogenated and dehydrogenated form of the hydride-the hydride hydrogenates the hydrocarbon and is dehydrogenated itself and afterwards takes up hydrogen from the atmosphere to be rehydrogenated. © 2008.

Palladium catalysts were synthesized in a highly controlled chemical vapor deposition process, giving narrowly distributed Pd nanoparticles with median sizes ranging from 1.3 to 5 nm on a SiO2 or TiO2 support. Unsupported Pd nanoparticles with median sizes between 3 and 9 nm were also generated by spark discharge. The influence of Pd particle size and support on the hydrogenation of ethene to ethane was investigated in a fixed-bed flow reactor at atmospheric pressure. The TOF was found to peak at 3 to 4 nm with a weak dependence on the support material. Metal support interactions were generally weak, indicated by closely matching activation energies of 20 kJ mol-1 for unsupported Pd, and 28 kJ mol-1 for titania and silica supported catalysts. Peak TOF values varied systematically with H2 partial pressure, indicating a pronounced volume effect of the Pd particles on the reactivity. © 2009 Elsevier Inc. All rights reserved.

A novel type of complex rare-earth aluminum hydride was prepared by mechanochemical preparation. The crystal structure of the REAlH6 (with RE = La, Ce, Pr, Nd) compounds was calculated by DFT methods and confirmed by preliminary structure refinements. The trigonal crystal structure consists of isolated [AlH6]3- octahedra bridged via [12] coordinated RE cations. The investigation of the rare-earth aluminum hydrides during thermolysis shows a decrease of thermal stability with increasing atomic number of the RE element. Rare-earth hydrides (REHx) are formed as primary dehydrogenation products; the final products are RE-aluminum alloys. The calculated decomposition enthalpies of the rare-earth aluminum hydrides are at the lower end for reversible hydrogenation under moderate conditions. Even though these materials may require somewhat higher pressures and/or lower temperatures for rehydrogenation, they are interesting examples of low-temperature metal hydrides for which reversibility might be reached. © 2009 American Chemical Society.

The density functional theory based molecular dynamics (DFTMD) method for the computation of redox free energies presented in previous publications and the more recent modification for computation of acidity constants are reviewed. The method uses a half reaction scheme based on reversible insertion/removal of electrons and protons. The proton insertion is assisted by restraining potentials acting as chaperones. The procedure for relating the calculated deprotonation free energies to Brønsted acidities (pKa) and the oxidation free energies to electrode potentials with respect to the normal hydrogen electrode is discussed in some detail. The method is validated in an application to the reduction of aqueous 1,4-benzoquinone. The conversion of hydroquinone to quinone can take place via a number of alternative pathways consisting of combinations of acid dissociations, oxidations, or dehydrogenations. The free energy changes of all elementary steps (ten in total) are computed. The accuracy of the calculations is assessed by comparing the energies of different pathways for the same reaction (Hess's law) and by comparison to experiment. This two-sided test enables us to separate the errors related with the restrictions on length and time scales accessible to DFTMD from the errors introduced by the DFT approximation. It is found that the DFT approximation is the main source of error for oxidation free energies. © 2009 American Institute of Physics.

Combining photoemission and electrochemical data from the literature we argue that the difference between the vertical and adiabatic ionization energy of the aqueous hydroxide anion is 2.9 eV. We then use density functional theory based molecular dynamics to show that the solvent response to ionization is nonlinear. Adding this to the experimental data we predict a 4.1 eV difference between the energy for vertical attachment of an electron to the aqueous hydroxyl radical and the corresponding adiabatic electron affinity. This places the state accepting the electron only 2.2 eV below vacuum or 7.7 eV above the edge of the valence band of water. © 2009 American Chemical Society.

Hydrogen is one possible medium for energy storage and transportation in an era beyond oil. Hydrogen appears to be especially promising in connection with electricity generation in polymer electrolyte membrane (PEM) fuel cells in cars. However, before such technologies can be implemented on a larger scale, satisfactory solutions for on-board storage of hydrogen are required. This is a difficult task due to the low volumetric and gravimetric storage density on a systems level which can be achieved so far. Possibilities include cryogenic storage as liquid hydrogen, high pressure storage at 70 MPa, (cryo)adsorptive storage, or various chemical methods of binding and releasing hydrogen. This survey discusses the different options and the associated advantages and disadvantages. © EDP Sciences and Springer 2009.