- Ruhr-Universität Bochum

Reactions between a gas phase and a solid material are of high importance in the study of alternative ways for energy conversion utilizing otherwise useless carbon dioxide (CO2). The photocatalytic CO2 reduction to hydrocarbon fuels like e.g., methane (CH4) is such a potential candidate process converting solar light into molecular bonds. In this work, the design, construction, and operation of a high-purity gas–solid photoreactor is described. The design aims at eliminating any unwanted carbon-containing impurities and leak points, ensuring the collection of reliable and reproducible data in photocatalytic CO2 reduction measurements. Apart from the hardware design, a detailed experimental procedure including gas analysis is presented, allowing newcomers in the field of gas–solid CO2 reduction to learn the essential basics and valuable tricks. By performing extensive blank measurements (with/without sample and/or light) the true performance of photocatalytic materials can be monitored, leading to the identification of trends and the proposal of possible mechanisms in CO2 photoreduction. The reproducibility of measurements between different versions of the here presented reactor on the ppm level is evidenced. © 2023 The Authors

For the development of a wearable artificial kidney (WAK) that uses a small dialysate volume that is continuously regenerated, it is essential that urea, one of the main uremic retention solutes, is removed. Despite advances in sorbent technology or electro-oxidation no safe, efficient and selective method for urea removal has been reported that allows miniaturization of the artificial kidney to wearable proportions. Here we have developed a flow cell for light-driven, photo-electrocatalytic (PEC) urea removal for use in a WAK. We use a photo-active material (hematite) coated with a catalyst (NiOOH) as working electrode for selective urea oxidation and a silver-chloride (AgCl) cathode. The use of the AgCl counter electrodes eliminates the need for an external bias voltage, and allows operation under light illumination only. Using LED illumination (460 nm) we show that urea is selectively oxidized over chloride. N2 formation is confirmed by gas-phase analysis of the headspace of the sample vial, using mass spectrometry. Other nitrogen containing products include nitrite but importantly ammonia and nitrate are not detected. Using the PEC concept a urea removal rate of 2.5 μmol/cm2h (or 0.15 mg/cm2h) has been achieved. Extrapolating our results to an upscaled system, a surface area of 0.5 m2 would enable efficient removal of the daily produced amount of urea (∼300 mmol) urea within 24 h, when driven by LED illumination only. © 2023 The Authors

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.

The measurement of diffusivity within porous solids is vital for the characterization of materials, especially in heterogeneous catalysis and separation processes. Numerous methods have been developed to measure gas-phase diffusivities within materials. However, establishing correlations between the diffusivities and the properties of a material is challenging. Herein, we report a method for obtaining trends in gas-phase diffusivity of N2 at 77 K within three different sets of mesoporous materials, disordered, ordered silica, and carbons-based materials. Synthesis procedures are reproducible and controlled precisely to achieve monodisperse particle size and defined pore size distributions. A standard physisorption device, Micromeritics 3Flex, is used to obtain the required transient data. These two aspects offer a suitable database of materials to identify trends and reduce the challenges associated with obtaining experimental data. A simplified model is fitted over the transient data with MATLAB to obtain empirical diffusivities used for trend analysis. The trends are based on a constant Dτ, an ensemble value representing various diffusion processes occurring during a transient uptake process. The analysis identifies several correlations between the diffusivity and properties of materials, such as type of pore structure, pore size, and the chemical nature of the material. Based on the principles reported, this study can be extended to other adsorptive molecules or different temperatures. The possibility of using standard sorption instrumentation will allow a broader user community to employ the reported methodology. © 2021 Elsevier Inc.

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

Creating high surface area nanocatalysts that contain stacking faults is a promising strategy to improve catalytic activity. Stacking faults can tune the reactivity of the active sites, leading to improved catalytic performance. The formation of branched metal nanoparticles with control of the stacking fault density is synthetically challenging. In this work, we demonstrate that varying the branch width by altering the size of the seed that the branch grows off is an effective method to precisely tune the stacking fault density in branched Ni nanoparticles. A high density of stacking faults across the Ni branches was found to lower the energy barrier for Ni2+/Ni3+oxidation and result in enhanced activity for electrocatalytic oxidation of 5-hydroxylmethylfurfural. These results show the ability to synthetically control the stacking fault density in branched nanoparticles as a basis for enhanced catalytic activity. © 2022 American Chemical Society. All rights reserved.

Water nucleation on alkali precovered metal-supported oxide surfaces is an important step in understanding water as one of the reactants in alkali-assisted heterogeneous catalysis. For instance, alkali metals as catalyst dopants enhance the water-gas shift reaction that catalyzes on ZnO-metal nanostructures. Here, we investigate the hydration of cesium on a Ag(111)-supported graphitic zinc oxide ultrathin film using scanning tunneling microscopy at (160 ± 30) K. Upon hydrating the pristine graphitic ZnO film, the water forms well-separated clusters on the hcp regions of the ZnO moiré pattern at water coverages below 85% ML. In the presence of cesium on the fcc regions of the ZnO moiré pattern, the water clusters coalesce across hcp regions at water coverages above ∼32% ML, forming unique one-dimensional water-Cs chains along the high-symmetry directions of the ZnO moiré pattern. Our study demonstrates that the alkali doping of an oxide surface alters the dimensionality of water structures redirecting it partially to other adsorption regions, possibly influencing its reactivity. © 2022 American Chemical Society.

Direct mechanocatalysis (DM) describes solvent-free catalytic reactions that are initiated by mechanical forces in mechanochemical reactors such as ball mills. The distinctive feature of DM is that the milling materials, e.g. the milling balls themselves are the catalyst of the reaction. In this article we follow the historical evolution of this novel concept and give a guide to this emerging, powerful synthesis tool. Within this perspective we seek to highlight the impact of the relevant milling parameters, the nature of the catalyst and potential additives, the scope of reactions that are currently accessible by this method, and the thus far raised hypotheses on the underlying mechanisms of direct mechanochemical transformations. © The Royal Society of Chemistry.

The molecular Suzuki cross-coupling reaction was conducted mechanochemically, without solvents, ligands, or catalyst powders. Utilizing one catalytically active palladium milling ball, products could be formed in quantitative yield in as little as 30 min. In contrast to previous reports, the adjustment of milling parameters led to the complete elimination of abrasion from the catalyst ball, thus enabling the first reported systematic catalyst analysis. XPS, in situ XRD, and reference experiments provided evidence that the milling ball surface was the location of the catalysis, allowing a mechanism to be proposed. The versatility of the approach was demonstrated by extending the substrate scope to deactivated and even sterically hindered aryl iodides and bromides. © 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.

The use of photosynthetic biohybrids to drive redox reactions in vitro is a promising strategy due to the natural abundance and high quantum efficiency of the bio-components. Here, we present different tools for the fabrication of photosystem I-based biohybrid devices by using redox-active polymers, 3D-structured electrodes as well as additional light-harvesting antennae modules. © 2022, Die Autorinnen und Autoren.

Electrocatalytic recycling of waste nitrate (NO3−) to valuable ammonia (NH3) at ambient conditions is a green and appealing alternative to the Haber−Bosch process. However, the reaction requires multi-step electron and proton transfer, making it a grand challenge to drive high-rate NH3 synthesis in an energy-efficient way. Herein, we present a design concept of tandem catalysts, which involves coupling intermediate phases of different transition metals, existing at low applied overpotentials, as cooperative active sites that enable cascade NO3−-to-NH3 conversion, in turn avoiding the generally encountered scaling relations. We implement the concept by electrochemical transformation of Cu−Co binary sulfides into potential-dependent core−shell Cu/CuOx and Co/CoO phases. Electrochemical evaluation, kinetic studies, and in−situ Raman spectra reveal that the inner Cu/CuOx phases preferentially catalyze NO3− reduction to NO2−, which is rapidly reduced to NH3 at the nearby Co/CoO shell. This unique tandem catalyst system leads to a NO3−-to-NH3 Faradaic efficiency of 93.3 ± 2.1% in a wide range of NO3− concentrations at pH 13, a high NH3 yield rate of 1.17 mmol cm−2 h−1 in 0.1 M NO3− at −0.175 V vs. RHE, and a half-cell energy efficiency of ~36%, surpassing most previous reports. © 2022, The Author(s).

The use of nanoparticles and nanostructured electrodes are abundant in electrocatalysis. These nanometric systems contain elements of nanoconfinement in different degrees, depending on the geometry, which can have a much greater effect on the activity and selectivity than often considered. In this Review, we firstly identify the systems containing different degrees of nanoconfinement and how they can affect the activity and selectivity of electrocatalytic reactions. Then we follow with a fundamental understanding of how electrochemistry and electrocatalysis are affected by nanoconfinement, which is beginning to be uncovered, thanks to the development of new, atomically precise manufacturing and fabrication techniques as well as advances in theoretical modeling. The aim of this Review is to help us look beyond using nanostructuring as just a way to increase surface area, but also as a way to break the scaling relations imposed on electrocatalysis by thermodynamics. © 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.

The use of enzymes as catalysts in chemical synthesis offers advantages in terms of clean and highly selective transformations. Galactose oxidase (GalOx) is a remarkable enzyme with several applications in industrial conversions as it catalyzes the oxidation of primary alcohols. We have investigated the wiring of GalOx with a redox polymer; this enables mediated electron transfer with the electrode surface for its potential application in biotechnological conversions. As a result of electrochemical regeneration of the catalytic center, the formation of harmful H2O2 is minimized during enzymatic catalysis. The introduced bioelectrode was applied to the conversion of bio-renewable platform materials, with glycerol as model substrate. The biocatalytic transformations of glycerol and 5-hydroxymethylfurfural (HMF) were investigated in a circular flow-through setup to assess the possibility of substrate over-oxidation, which is observed for glycerol oxidation but not during HMF conversion. © 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.

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

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.

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.

The purpose of this study is to find a direct and quantitative correlation of the structure of Co3-xFexO4nanoparticles with catalytic performance in 2-propanol oxidation. Eight nanocrystalline samples with varying iron contents are synthesized, and quantitative information regarding their structure is obtained from nitrogen physisorption, X-ray diffraction (XRD), X-ray absorption near-edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) analyzed by reverse Monte Carlo simulations. The catalytic performance is tested in 2-propanol oxidation in the gas phase. Overall, catalytic conversion data as a function of temperature are deconvoluted to obtain conversion and half-conversion temperatures as quantitative parameters for the different catalytic reaction channels. The crystal structure is described by a spinel structure with interstitial cation defects. These defects result in a reduced electronic state of the nanoparticles. The defect density depends on the cationic composition. We also observe a complex cationic distribution on tetrahedral and octahedral sites, which is strongly influenced by the overall cationic composition. In the catalytic tests, the samples exhibit a low-temperature pathway, which is deactivated in subsequent runs but can be recovered by an oxidative treatment of the catalyst. We find that the frequency of cation pairs CoO-CoOand CoO-CoTof the individual samples correlates directly to their catalytic activity and selectivity. © 2022 American Chemical Society. All rights reserved.

The distribution of water on metal supported oxides is an important step in understanding heterogeneous catalysis such as in the water gas shift reaction. Here, we study water structures on Ag(111)-supported graphitic zinc oxide islands by variable temperature scanning tunneling microscopy around 150 K and ab initio calculations. Water clusters, accumulating on the ZnO islands, are confined to the hcp regions of the ZnO moiré pattern. A significantly higher cluster density at the island border is related to the dimensions of its capture zone. This suggests an upward mass transport of the water from the supporting metal to the ultrathin oxide film, increasing the water density at the active metal-oxide border. © 2022 American Chemical Society. All rights reserved.

Current energy and environmental challenges demand the development and design of multifunctional porous materials with tunable properties for catalysis, water purification, and energy conversion and storage. Because of their amenability to de novo reticular chemistry, metal-organic frameworks (MOFs) have become key materials in this area. However, their usefulness is often limited by low chemical stability, conductivity and inappropriate pore sizes. Conductive two-dimensional (2D) materials with robust structural skeletons and/or functionalized surfaces can form stabilizing interactions with MOF components, enabling the fabrication of MOF nanocomposites with tunable pore characteristics. Graphene and its functional derivatives are the largest class of 2D materials and possess remarkable compositional versatility, structural diversity, and controllable surface chemistry. Here, we critically review current knowledge concerning the growth, structure, and properties of graphene derivatives, MOFs, and their graphene@MOF composites as well as the associated structure-property-performance relationships. Synthetic strategies for preparing graphene@MOF composites and tuning their properties are also comprehensively reviewed together with their applications in gas storage/separation, water purification, catalysis (organo-, electro-, and photocatalysis), and electrochemical energy storage and conversion. Current challenges in the development of graphene@MOF hybrids and their practical applications are addressed, revealing areas for future investigation. We hope that this review will inspire further exploration of new graphene@MOF hybrids for energy, electronic, biomedical, and photocatalysis applications as well as studies on previously unreported properties of known hybrids to reveal potential "diamonds in the rough". ©

The propagation and interaction between surface streamers propagating over dielectric pellets in a packed bed plasma reactor operated in Helium are studied using phase and space resolved optical emission spectroscopy and simulations. Such a discharge is known to generate cathode directed positive streamers in the gas phase at the positions of minimum electrode gap followed by surface streamers that propagate along the dielectric surface. By systematically varying the gap between neighboring dielectric pellets, we observe that a larger gap between adjacent dielectric pellets enhances plasma emission near the contact points of the dielectric structures. In agreement with the experiment, the simulation results reveal that the gap influences the attraction of streamers towards adjacent dielectric pellets via polarization of the surface material and the repulsion induced by nearby streamers. For a smaller gap, the streamer propagation changes from along the surface to propagation through the volume and back to surface propagation due to a combination of repulsion between adjacent streamers, polarization of adjacent dielectric surfaces, as well as acceleration of electrons from the volume towards the streamer head. For a wider gap, the streamer propagates along the surface, but repulsion by neighboring streamers increases the offset between the streamers. The streamer achieves a higher speed near the contact point earlier in the absence of an adjacent streamer, which indicates the role of mutual streamer interaction via repulsion. © 2022 The Author(s). Published by IOP Publishing Ltd.

The unique structural and electronic properties of transition metal dichalcogenides (TMDs) and in particular tungsten disulphide (WS2) make them interesting for a variety of applications such as the electrocatalytic hydrogen evolution reaction (HER) for water splitting devices and chemiresistive gas sensors. The key parameter for the realisation of these devices is the controlled large-area growth of WS2 combined with tuning the surface morphology and electronic properties which is achieved by bottom-up fabrication methods such as chemical vapour deposition (CVD). In this study, 2H-WS2 films are fabricated by a new metal-organic CVD (MOCVD) process resulting in the growth of crystalline, pure, and stoichiometric films which was accomplished at temperatures as low as 600 °C as confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectrometry (RBS)/nuclear reaction analysis (NRA), and Raman spectroscopy. The surface morphology of WS2 layers was investigated by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM). Following successful process development, the WS2 layers were deposited on conducting FTO/glass substrates and their catalytic activity for the HER was evaluated in a linear sweep voltammetry (LSV) experiment. Furthermore, the temperature-dependent sensor response towards NO2, CO, and NH3 was investigated for WS2 films deposited on special sensor chips, revealing a p-type response towards NO2 and NH3 and sensitivities of around 20% for NO2 and NH3 concentrations of 1.5 ppm and 7.6 ppm, respectively. These promising results demonstrate the effectiveness of scalable CVD-grown WS2 and pave the way for practical applications by modulating the properties of materials to achieve enhanced electrocatalytic and sensing performances employing WS2 layers. © 2021 The Royal Society of Chemistry.

The influence of the drop-casted nickel boride catalyst loading on glassy carbon electrodes was investigated in a spectroelectrochemical ATR-FTIR thin-film flow cell applied in alkaline glycerol electrooxidation. The continuously operated radial flow cell consisted of a borehole electrode positioned 50 µm above an internal reflection element enabling operando FTIR spectroscopy. It is identified as a suitable tool for facile and reproducible screening of electrocatalysts under well-defined conditions, additionally providing access to the selectivities in complex reaction networks such as glycerol oxidation. The fast product identification by ATR-IR spectroscopy was validated by the more time-consuming quantitative HPLC analysis of the pumped electrolyte. High degrees of glycerol conversion were achieved under the applied laminar flow conditions using 0.1 M glycerol and 1 M KOH in water and a flow rate of 5 µL min−1. Conversion and selectivity were found to depend on the catalyst loading, which determined the catalyst layer thickness and roughness. The highest loading of 210 µg cm−2 resulted in 73% conversion and a higher formate selectivity of almost 80%, which is ascribed to longer residence times in rougher films favoring readsorption and C–C bond scission. The lowest loading of 13 µg cm−2 was sufficient to reach 63% conversion, a lower formate selectivity of 60%, and, correspondingly, higher selectivities of C2 species such as glycolate amounting to 8%. Thus, only low catalyst loadings resulting in very thin films in the few μm thickness range are suitable for reliable catalyst screening. © 2021 Dalian Institute of Chemical Physics, the Chinese Academy of Sciences

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

"Why?"is the question that initiates science. "Why?"is also the answer that maintains science. This interrogative adverb fuels the scientific career of Robert Schlögl. Robert is a dedicated solid-state chemist who has found his specialization in untangling the working principles of heterogeneous catalysts under realistic conditions. As such he combines the full complexity of real catalysts with tailor-made operando experiments to overcome pressure, material, and complexity gaps. His ability to quickly abstract the meaning of spectroscopic and microscopic data, his talent to ask the right question paired with curiosity, diligence, and creativity have made him a world-leading expert in heterogeneous catalysis and energy science. His scientific passion is focused on untangling chemical dynamics as well as working principles and understanding the important interplay of geometric and electronic structures in functional materials. Thereby his research interests involve ammonia and methanol synthesis, carbon materials in catalysis, hydrogenation, and dehydrogenation, selective oxidation, and the development of operando setups for microscopy and spectroscopy. He also has a strong commitment to society in scientifically accelerating the energy transition ("Energiewende") in Europe, where he focuses on CO2 utilization and hydrogen as an energy carrier. This is manifested in three recent large Germany-wide projects: Carbon2Chem, CatLab, and TransHyDe. ©

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).

Over the past two decades mechanochemistry has emerged as an important tool in catalysis research. It has not only shown promise for catalyst synthesis, resulting in properties that are often unattainable by conventional methods, but is also a very effective tool for performing catalytic reactions with exceptional selectivities. Besides, in several instances, it allows reactions under much milder conditions compared to thermochemical methods. In this chapter, we attempt to give an overview of these efforts with a focus on catalytic reactions in ball mills. Through the selection of prominent examples from the literature, from early mentions in 300 B.C. to recent times, we try to analyze how mechanical forces lead to chemical reactions and what effect they cause to materials or chemical reactions. We also discuss the state-of-the-art milling devices, and then cover broadly chemical reactions in ball mills. The latter part briefly tackles materials synthesis, but mainly focuses on chemical reactions of solid-solid and gas-solid nature from both organic synthesis and heterogeneous catalysis. The chapter also touches on the aspects of in situ analysis and scale-up with relevant literature. The latter areas are currently in the focus of attention to develop deeper understanding and to eventually find ways to make mechanocatalysis industrially applicable. © The Royal Society of Chemistry 2021.

Hydrocarbon exhaust gases containing residual amounts of oxygen may pose challenges for their conversion into value added chemicals downstream, because oxygen may affect the process. This could be avoided by plasma treating the exhaust to convert O 2 in presence of hydrocarbons into CO or CO 2 on demand. The underlying reaction mechanisms of plasma conversion of O 2 in the presence of hydrocarbons are analysed in a model experiment using a radio frequency atmospheric pressure helium plasma in a plug flow design with admixtures of O 2 and of CH 4. The plasma process is analysed with infrared absorption spectroscopy to monitor CH 4 as well as the reaction products CO, CO 2 and H 2O. It is shown that the plasma reaction for oxygen (or methane removal) is triggered by the formation of oxygen atoms from O 2 by electron. Oxygen atoms are efficiently converted into CO, CO 2 and H 2O with CO being an intermediate in that reaction sequence. However, at very high oxygen admixtures to the gas stream, the conversion efficiency saturates because electron induced O 2 dissociation in the plasma seems to be counterbalanced by a reduction of the efficiency of electron heating at high admixtures of O 2. The impact of a typical industrial manganese oxide catalyst is evaluated for methane conversion. It is shown that the conversion efficiency is enhanced by 15–20% already at temperatures of 430 K. © 2021, The Author(s).

[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).

Complex solid solution (CSS) (often denoted as high-entropy alloy) electrocatalysts enable access to unique possibilities for tailoring active sites while overcoming ever-existing limitations in electrocatalysis by unique interactions of various elements in direct neighborhood. The challenge lies in the development of strategies, which allow for systematic design of element combination and composition optimization in the multinary composition space. This challenge is accompanied by a lack of a suitable analysis method of experimental activity measurements, which can cope with the complex surface structure of this catalyst class. In this work, we propose the advantageous use of inflection points of voltammetric activity curves as activity descriptors enabling to correlate the potential of individual surface site groups to the respective peaks in the adsorption energy distribution pattern. This concept allows to methodologically gather information about the importance of each element in a CSS with respect to activity and stability of the relevant active sites and provides the basis for a guideline for systematic composition optimization. Further, the effect of phase stability on specific surface site groups as induced by degradation of the CSS phase or oxidation can be monitored. These concepts are experimentally evaluated using Cr-Mn-Fe-Co-Ni as a model system. Nanoparticles are synthesized with systematically varied compositions by means of scalable laser ablation synthesis using a multinary target. The composition is optimized with respect to the electrocatalytic activity for the oxygen reduction reaction (ORR) by varying its Mn content via laser ablation synthesis in ethanol. Subsequently, the concept is applied using rotating disk electrodes for ORR analysis in alkaline media. © 2021 American Chemical Society. All rights reserved.

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.

Nano-electrochemical tools to assess individual catalyst entities are critical to comprehend single-entity measurements. The intrinsic electrocatalytic activity of an individual well-defined Co3O4 nanoparticle supported on a carbon-based nanoelectrode is determined by employing an efficient SEM-controlled robotic technique for picking and placing a single catalyst particle onto a modified carbon nanoelectrode surface. The stable nanoassembly is microscopically investigated and subsequently electrochemically characterized. The hexagonal-shaped Co3O4 nanoparticles demonstrate size-dependent electrochemical activity and exhibit very high catalytic activity with a current density of up to 11.5 A cm−2 at 1.92 V (vs. RHE), and a turnover frequency of 532±100 s−1 at 1.92 V (vs. RHE) towards catalyzing the oxygen evolution reaction. © 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH

Co3O4 nanocubes are evaluated concerning their intrinsic electrocatalytic activity towards the oxygen evolution reaction (OER) by means of single-entity electrochemistry. Scanning electrochemical cell microscopy (SECCM) provides data on the electrocatalytic OER activity from several individual measurement areas covering one Co3O4 nanocube of a comparatively high number of individual particles with sufficient statistical reproducibility. Single-particle-on-nanoelectrode measurements of Co3O4 nanocubes provide an accelerated stress test at highly alkaline conditions with current densities of up to 5.5 A cm−2, and allows to derive TOF values of up to 2.8×104 s−1 at 1.92 V vs. RHE for surface Co atoms of a single cubic nanoparticle. Obtaining such high current densities combined with identical-location transmission electron microscopy allows monitoring the formation of an oxy(hydroxide) surface layer during electrocatalysis. Combining two independent single-entity electrochemistry techniques provides the basis for elucidating structure–activity relations of single electrocatalyst nanoparticles with well-defined surface structure. © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH

The formation of a vast number of different multielement active sites in compositionally complex solid solution materials, often more generally termed high-entropy alloys, offers new and unique concepts in catalyst design, which mitigate existing limitations and change the view on structure–activity relations. We discuss these concepts by summarising the currently existing fundamental knowledge and critically assess the chances and limitations of this material class, also highlighting design strategies. A roadmap is proposed, illustrating which of the characteristic concepts could be exploited using which strategy, and which breakthroughs might be possible to guide future research in this highly promising material class for (electro)catalysis. © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH

To understand corrosion, energy storage, (electro)catalysis, etc., obtaining chemical information on the solid-liquid interface is crucial but remains extremely challenging. Here, X-ray absorption spectroscopy (XAS) is used to study the solid-liquid interface between TiO2 and H2O. A thin film (6.7 nm) of TiO2 is deposited on an X-ray-transparent SiNx window, acting as the working electrode in a three-electrode flow cell. The spectra are collected based on the electron emission resulting from the decay of the X-ray-induced core-hole-excited atoms, which we show is sensitive to the solid-liquid interface within a few nm. The drain currents measured at the working and counter electrodes are identical but of opposite sign. With this method, we found that the water layer next to anatase is spectroscopically similar to ice. This result highlights the potential of electron-yield XAS to obtain chemical and structural information with a high sensitivity for the species at the electrode-electrolyte interface. © 2021 The Authors. Published by American Chemical Society.

Single-entity electrochemistry allows for assessing electrocatalytic activities of individual material entities such as nanoparticles (NPs). Thus, it becomes possible to consider intrinsic electrochemical properties of nanocatalysts when researching how activity relates to physical and structural material properties. Conversely, conventional electrochemical techniques provide a normal-ized sum current referring to a huge ensemble of NPs constituting, along with additives (e.g., bind-ers), a complete catalyst-coated electrode. Accordingly, recording electrocatalytic responses of single NPs avoids interferences of ensemble effects and reduces the complexity of electrocatalytic pro-cesses, thus enabling detailed description and modelling. Herein, we present insights into the oxygen evolution catalysis at individual cubic Co3O4 NPs impacting microelectrodes of different support materials. Simulating diffusion at supported nanocubes, measured step current signals can be analyzed, providing edge lengths, corresponding size distributions, and interference-free turnover frequencies. The provided nano-impact investigation of (electro-)catalyst-support effects contra-dicts assumptions on a low number of highly active sites. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

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).

Understanding structure and function of solid–liquid interfaces is essential for the development of nanomaterials for various applications including heterogeneous catalysis in liquid phase processes and water splitting for storage of renewable electricity. The characteristic anisotropy of crystalline nanoparticles is believed to be essential for their performance but remains poorly understood and difficult to characterize. Dual scale atomic force microscopy is used to measure electrostatic and hydration forces of faceted semiconducting SrTiO3 nanoparticles in aqueous electrolyte at variable pH. The following are demonstrated: the ability to quantify strongly facet-dependent surface charges yielding isoelectric points of the dominant {100} and {110} facets that differ by as much as 2 pH units; facet-dependent accumulation of oppositely charged (SiO2) particles; and that atomic scale defects can be resolved but are in fact rare for the samples investigated. Atomically resolved images and facet-dependent oscillatory hydration forces suggest a microscopic charge generation mechanism that explains colloidal scale electrostatic forces. © 2021 The Authors. Advanced Materials 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

Due to the high demand for renewable and infrastructure compatible energy conversion and storage technologies, research on organic fuel cells receives increasing interest again recently. Organic fuels such as alcohols provide an attractive avenue to overcome the drawbacks of hydrogen as an energy carrier. Particularly interesting are secondary alcohols that almost exclusively form ketones as the final oxidation product, as they can be utilized in “zero emission” concepts without CO2 as a by-product. The state-of-the-art electrocatalyst in secondary alcohol oxidation is Pt-Ru, which demonstrates low onset potentials for the oxidation of the most facile secondary alcohol isopropanol. Yet, the achievable current densities are still relatively low and decrease rapidly due to the formed product acetone, which can poison the catalyst surface over time. Therefore, there is an inevitable need for the development of novel electrocatalyst materials circumventing these challenges. In this study, we employ a high-throughput electrochemical approach coupled to on-line inductively-coupled plasma mass spectrometry to map the composition-dependent activity and stability of PtxIr100-x alloy electrocatalysts toward the electro-oxidation of isopropanol. The activity and stability of magnetron sputtered PtxIr100-x material libraries are studied in 0.1 M HClO4 both in the absence and presence of isopropanol. The highest current densities are achieved for the sample containing the least amount of Ir (3.4 at.%), with a continuous decrease with the increasing amount of Ir. The alloys are inactive towards the oxidation of isopropanol when the amount of Ir exceeded 80 at%. The presence of isopropanol also has a notable effect on stability: while dissolution rates do not change in the case of pure Pt and Ir, a significant increase in stability is observed for the PtxIr100-x thin-film samples at all applied upper potential limits. This is explained by the strong adsorption of acetone on the surface of the catalyst that inhibits the formation of surface oxides. © 2021 Elsevier Inc.

The complex interplay of restricted mass transport leading to local accumulation or depletion of educts, intermediates, products, counterions and co-ions influences the reactions at the active sites of electrocatalysts when electrodes are rough, three-dimensionally mesoporous or nanoporous. This influence is important with regard to activity, and even more to selectivity, of electrocatalytic reactions. The underlying principles are discussed based on the growing awareness of these considerations over recent years. © 2020 Elsevier B.V.

Plasma catalysis, the combination of plasma and catalysis, is used to achieve efficient molecule conversion, supporting the flexibility of operating parameters and feed gases. By combining plasmas with conventional thermal catalysis, the temperature windows may be changed and the process may be made insensitive to catalyst poisoning. However, understanding plasma catalysis mechanisms is extremely difficult, due to the strong coupling between plasma, gas-phase chemistry and surface. A multitude of reaction pathways may be enhanced or reduced by the presence of a plasma that provides excited species as reaction partners. We developed a robust setup to analyse those processes, based on a parallel-plate atmospheric-pressure plasma jet that allows a plug flow design. The plasma chemistry is analysed by Fourier transform infrared absorption spectroscopy and mass spectrometry. The electrodes in contact with the plasma are temperature controlled and can easily be replaced to apply a catalyst on top of them. The basic characteristics of the setup are discussed and three examples for its application are given: (a) the analysis of methane oxidation using the plug flow scheme; (b) the plasma catalytic conversion of CO2, and (c) the plasma catalytic conversion of methane in methane–oxygen mixtures. © 2021 IOP Publishing Ltd.

The aim to produce highly active, selective, and long-lived electrocatalysts by design drives major research efforts toward gaining fundamental understanding of the relationship between material properties and their catalytic performance. Surface characterization tools enable to assess atomic scale information on the complexity of electrocatalyst materials. Advancing electrochemical methodologies to adequately characterize such systems was less of a research focus point. In this Review, we shed light on the ability to gain fundamental insights into electrocatalysis from a complementary perspective and establish corresponding design strategies. These may rely on adopting the perceptions and models of other subareas of electrochemistry, such as corrosion, battery research, or electrodeposition. Concepts on how to account for and improve mass transport, manage gas bubble release, or exploit magnetic fields are highlighted in this respect. Particular attention is paid to deriving design strategies for nanoelectrocatalysts, which is often impeded, as structural and physical material properties are buried in electrochemical data of whole electrodes or even devices. Thus, a second major approach focuses on overcoming this difference in the considered level of complexity by methods of single-entity electrochemistry. The gained understanding of intrinsic catalyst performance may allow to rationally advance design concepts with increased complexity, such as three-dimensional electrode architectures. Many materials undergo structural changes upon formation of the working catalyst. Accordingly, developing "precatalysts"with low hindrance of the electrochemical transformation to the active catalyst is suggested as a final design strategy. ©

Developing highly efficient and selective electrocatalysts for the CO2 reduction reaction to produce value-added chemicals has been intensively pursued. We report a series of CuxOyCz nanostructured electrocatalysts derived from a Cu-based MOF as porous self-sacrificial template. Blending catalysts with polytetrafluoroethylene (PTFE) on gas diffusion electrodes (GDEs) suppressed the competitive hydrogen evolution reaction. 25 to 50 wt % teflonized GDEs exhibited a Faradaic efficiency of ≈54 % for C2+ products at −80 mA cm−2. The local OH− ions activity of PTFE-modified GDEs was assessed by means of closely positioning a Pt-nanoelectrode. A substantial increase in the OH−/H2O activity ratio due to the locally generated OH− ions at increasing current densities was determined irrespective of the PTFE amount. © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH

Complex solid solutions (“high entropy alloys”), comprising five or more principal elements, promise a paradigm change in electrocatalysis due to the availability of millions of different active sites with unique arrangements of multiple elements directly neighbouring a binding site. Thus, strong electronic and geometric effects are induced, which are known as effective tools to tune activity. With the example of the oxygen reduction reaction, we show that by utilising a data-driven discovery cycle, the multidimensionality challenge raised by this catalyst class can be mastered. Iteratively refined computational models predict activity trends around which continuous composition-spread thin-film libraries are synthesised. High-throughput characterisation datasets are then used as input for refinement of the model. The refined model correctly predicts activity maxima of the exemplary model system Ag-Ir-Pd-Pt-Ru. The method can identify optimal complex-solid-solution materials for electrocatalytic reactions in an unprecedented manner. © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH

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

Nanoparticles have become increasingly interesting for a wide range of applications because in principle it is possible to tailor their properties by controlling size, shape, and composition. One of these applications is heterogeneous catalysis, and a fundamental understanding of the structural details of the nanoparticles is essential for any knowledge-based improvement of reactivity and selectivity. In this work, we investigate the atomic structure of brass nanoparticles containing up to 5000 atoms as a typical example for a binary alloy consisting of Cu and Zn. As systems of this size are too large for electronic structure calculations, in our simulations, we use a recently parameterized machine learning potential providing close to density functional theory accuracy. This potential is employed for a structural characterization as a function of chemical composition by various types of simulations such as Monte Carlo in the semigrand canonical ensemble and simulated annealing molecular dynamics. Our analysis reveals that the distribution of both elements in the nanoparticles is inhomogeneous, and zinc accumulates in the outermost layer, while the first subsurface layer shows an enrichment of copper. Only for high zinc concentrations, alloying can be found in the interior of the nanoparticles, and regular patterns corresponding to crystalline bulk phases of α-brass can then be observed. The surfaces of the investigated clusters exhibit well-ordered single-crystal facets, which can give rise to grain boundaries inside the clusters. The melting temperature of the nanoparticles is found to decrease with increasing zinc-atom fraction, a trend which is well known also for the bulk phase diagram of brass. © 2021 The Authors. Published by American Chemical Society.

Direct mechanocatalysis describes catalytic reactions under the involvement of mechanical energy with the distinct feature of milling equipment itself being the catalyst. This novel type of catalysis features no solubility challenges of the catalysts nor the substrate and on top offering most facile way of separation. © 2020 The Authors. Published by Wiley-VCH GmbH

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.

Carbon corrosion at high anodic potentials is a major source of instability, especially in acidic electrolytes and impairs the long-term functionality of electrodes. In-depth investigation of carbon corrosion in alkaline environment by means of differential electrochemical mass spectrometry (DEMS) is prevented by the conversion of CO2 into CO3 2−. We report the adaptation of a DEMS system for online CO2 detection as the product of carbon corrosion in alkaline electrolytes. A new cell design allows for in situ acidification of the electrolyte to release initially dissolved CO3 2− as CO2 in front of the DEMS membrane and its subsequent detection by mass spectrometry. DEMS studies of a carbon-supported nickel boride (NixB/C) catalyst and Vulcan XC 72 at high anodic potentials suggest protection of carbon in the presence of highly active oxygen evolution electrocatalysts. Most importantly, carbon corrosion is decreased in alkaline solution. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

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

Intensive research is being conducted into highly efficient and cheap nanoscale materials for the electrocatalytic oxidation of water. In this context, we built heterostructures of multilayered CoNi-cyanide bridged coordination (CoNi-CP) nanosheets and graphene oxide (GO) sheets (CoNi-CP/GO) as a source for heterostructured functional electrodes. The layered CoNi-CP/GO hybrid components heated in nitrogen gas (N2) at 450 °C yield CoNi-based carbide (CoNi-C) through thermal decomposition of CoNi-CP, while GO is converted into reduced GO (rGO) to finally form a CoNi-C/rGO-450 composite. The CoNi-C/rGO-450 composite shows a reasonable efficiency for oxygen evolution reaction (OER) through water oxidations in alkaline solution. Meanwhile, regulated annealing of CoNi-CP/GO in N2 with thiourea at 450 and 550 °C produces CoNi-based sulfide (CoNi-S) rather than CoNi-C between rGO sheets co-doped by nitrogen (N) and sulfur (S) heteroatoms (NS-rGO) to form CoNi-S/NS-rGO-450 and CoNi-S/NS-rGO-550 composites, respectively. The CoNi-S/NS-rGO-550 shows the best efficiency for electrocatalytic OER among all electrodes with an overpotential of 290 mV at 10 mA cm-2 and a Tafel slope of 79.5 mV dec-1. By applying the iR compensation to remove resistance of the solution (2.1 ω), the performance is further improved to achieve a current density of 10 mA cm-2 at an overpotential of 274 mV with a Tafel slope of 70.5 mV dec-1. This result is expected to be a promising electrocatalyst compared to the currently used electrocatalysts and a step for fuel cell applications in the future. © 2020 American Chemical Society.

A light-controlled multiplexing platform has been developed on the basis of a quantum dot-sensitized inverse opal TiO2electrode with integrated biocatalytic reactions. Spatially resolved illumination enables multiplexed sensing and imaging of enzymatic oxidation reactions at relatively negative applied potentials. © The Royal Society of Chemistry 2020.

In this work, spectroscopic and kinetic studies were performed on photocatalytic oxidation of cyclohexanol to cyclohexanone. The photocatalytic experiments were performed according to a three-level full factorial design and the rate of cyclohexanone production was determined by HPLC analysis. In situ ATR-FTIR analysis of the photocatalytic reaction revealed that cyclohexanol can be selectively converted to cyclohexanone, without the formation of significant amounts of carbonates and carboxylates. A reaction mechanism based on different steps from charge separation to cyclohexanone molecule formation is proposed. The results were utilized to determine the kinetic parameters (with the help of genetic algorithm) and validate the model. The developed kinetic model illustrates that the rate of cyclohexanone production increases as a power function with respect to the light intensity and decreases as an exponential function with respect to time. An excellent selectivity of cyclohexanone was confirmed by spectroscopic and chromatographic studies. This study demonstrates that photocatalysis can be a promising technology for formation of cyclohexanone from cyclohexanol. © 2019 Elsevier B.V.

Carbon is a frequently used electrode material and an important additive in catalyst films. Its corrosion is often reported during electrocatalysis at high anodic potentials, especially in acidic electrolyte. Investigation of the carbon corrosion in alkaline environment is difficult due to the CO2/CO32− equilibrium. We report the on-line determination of electrolysis products generated on NixB/C hybrid electrocatalysts in alkaline electrolyte at anodic potentials using differential electrochemical mass spectrometry (DEMS). NixB/C catalyst films were obtained from mixtures containing different ratios of NiXB and benzoxazine monomers followed by polymerization and pyrolysis. The impact of the composition of the electrocatalyst on the dominant electrolysis process allows to distinguish between the oxygen evolution reaction and carbon corrosion using DEMS results as well as the catalyst surface composition evaluated from X-ray photoelectron spectra. At the imposed highly oxidative conditions, an increasing amount of NixB in the electrocatalyst leads to a suppression of carbon corrosion. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

The use of rotating disk electrodes modified with multicomponent catalyst inks is common practice in electrocatalysis. In this work, we present a numerical model to simulate the effect of altered mass transport and conductivity inside a catalyst film, consisting of catalytically active nanoparticles and an inert binder material. Implications for the classical Tafel analysis are evaluated at different combinations of film resistances and mass transport properties. We show that in some cases, linear Tafel-like voltammetric responses may result, which do not contain actual kinetic information and might therefore be misleading and cause of erroneous catalyst activity evaluation. © 2020 Elsevier B.V.

The use of a microscale atmospheric pressure plasma jet (μAPPJ) was investigated for its potential to supply hydrogen peroxide in biocatalysis. Compared to a previously employed dielectric barrier discharge (DBD), the μAPPJ offered significantly higher H2O2 production rates and better handling of larger reaction volumes. The performance of the μAPPJ was evaluated with recombinant unspecific peroxygenase from Agrocybe aegerita (rAaeUPO). Using plasma-treated buffer, no side reactions with other plasma-generated species were detected. For long-term treatment, rAaeUPO was immobilized, transferred to a rotating bed reactor, and reactions performed using the μAPPJ. The enzyme had a turnover of 36,415 mol mol−1 and retained almost full activity even after prolonged plasma treatment. Overall, the μAPPJ presents a promising plasma source for plasma-driven biocatalysis. © 2020 The Authors. Published by Wiley-VCH GmbH

We report an organic redox-polymer-based electroenzymatic nitrogen fixation system using a metal-free redox polymer, namely neutral-red-modified poly(glycidyl methacrylate-co-methylmethacrylate-co-poly(ethyleneglycol)methacrylate) with a low redox potential of −0.58 V vs. SCE. The stable and efficient electric wiring of nitrogenase within the redox polymer matrix enables mediated bioelectrocatalysis of N3−, NO2− and N2 to NH3 catalyzed by the MoFe protein via the polymer-bound redox moieties distributed in the polymer matrix in the absence of the Fe protein. Bulk bioelectrosynthetic experiments produced 209±30 nmol NH3 nmol MoFe−1 h−1 from N2 reduction. 15N2 labeling experiments and NMR analysis were performed to confirm biosynthetic N2 reduction to NH3. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

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.

Bioelectrocatalysis provides access to sustainable and highly efficient technological applications. However, several limitations related either to the intrinsic properties of the biocatalyst or to technical difficulties still hamper or even prevent the integration of such devices into technologically relevant large-scale processes. In this Review, we challenge the common viewpoint suggesting biology-based catalytic systems as a promising approach for the provision of sustainable stored energy and discuss the status of bioelectrocatalytic devices developed for energy conversion. In particular, we focus on two major research areas in the field, that is, H2-powered hydrogenase-based biofuel cells and biophotoelectrodes for solar energy harvesting. We identify the main limitations that have to be addressed to gain access to applied large-scale bio-based and bio-inspired advanced energy conversion systems. Moreover, we show recent examples and milestones that are paving the way towards potential realization of these technologies by overcoming existing limiting factors. © 2019, Springer Nature Limited.

The chemical composition and the electronic state of the surface of alloys or mixed oxides with enhanced electrocatalytic properties are usually heterogeneous at the nanoscale. The non-uniform distribution of the potential across their surface affects both activity and stability. Studying such heterogeneities at the relevant length scale is crucial for understanding the relationships between structure and catalytic behaviour. Here, we demonstrate an experimental approach combining scanning photoemission electron microscopy and atom probe tomography performed at identical locations to characterise the surface's structure and oxidation states, and the chemical composition of the surface and sub-surface regions. Showcased on an Ir-Ru thermally grown oxide, an efficient catalyst for the anodic oxygen evolution reaction, the complementary techniques yield consistent results in terms of the determined surface oxidation states and local oxide stoichiometry. Significant chemical heterogeneities in the sputter-deposited Ir-Ru alloy thin films govern the oxide's chemistry, observed after thermal oxidation both laterally and vertically. While the oxide grains have a composition of Ir0.94Ru0.06O2, the composition in the grain boundary region varies from Ir0.70Ru0.30O2 to Ir0.40Ru0.60O2 and eventually to Ir0.75Ru0.25O2 from the top surface into the depth. The influence of such compositional non-uniformities on the catalytic performance of the material is discussed, along with possible engineering levers for the synthesis of more stable and reactive mixed oxides. The proposed method provides a framework for investigating materials of interest in the field of electrocatalysis and beyond. This journal is © The Royal Society of Chemistry.

Producing stable but active materials is one of the enduring challenges in electrocatalysis and other types of catalysis. Producing branched nanoparticles is one potential solution. Controlling the number of branches and branch size of faceted branched nanoparticles is one of the major synthetic challenges to achieve highly active and stable nanocatalysts. Herein, we use a cubic-core hexagonal-branch mechanism to synthesize branched Ru nanoparticles with control over the size and number of branches. This structural control is the key to achieving high exposure of active {10–11} facets and optimum number of Ru branches that enables improved catalytic activity for oxygen evolution reaction while maintaining high stability. © 2020 Wiley-VCH GmbH

Cryptomelane (α-(K)MnO2) powders were synthesized by different methods leading to only slight differences in their bulk crystal structure and chemical composition, while the BET surface area and the crystallite size differed significantly. Their performance in the oxygen evolution reaction (OER) covered a wide range and their sequence of increasing activity differed when electrocatalysis in alkaline electrolyte and chemical water oxidation using Ce4+ were compared. The decisive factors that explain this difference were identified in the catalysts’ microstructure. Chemical water oxidation activity is substantially governed by the exposed surface area, while the electrocatalytic activity is determined largely by the electric conductivity, which was found to correlate with the particle morphology in terms of needle length and aspect ratio in this sample series. This correlation is rather explained by an improved conductivity due to longer needles than by structure sensitivity as was supported by reference experiments using H2O2 decomposition and carbon black as additive. The most active catalyst R-cryptomelane reached a current density of 10 mA cm−2 at a potential 1.73 V without, and at 1.71 V in the presence of carbon black. The improvement was significantly higher for the catalyst with lower initial activity. However, the materials showed a disappointing catalytic stability during alkaline electrochemical OER, whereas the crystal structure was found to be stable at working conditions. © 2020 The Authors. Published by Wiley-VCH GmbH

Electrocatalytic nanoparticles that mimic the three-dimensional geometric architecture of enzymes where the reaction occurs down a substrate channel isolated from bulk solution, referred to herein as nanozymes, were used to explore the impact of nano-confinement on electrocatalytic reactions. Surfactant covered Pt-Ni nanozyme nanoparticles, with Ni etched from the nanoparticles, possess a nanoscale channel in which the active sites for electrocatalysis of oxygen reduction are located. Different particle compositions and etching parameters allowed synthesis of nanoparticles with different average substrate channel diameters that have varying amounts of nano-confinement. The results showed that in the kinetically limited regime at low overpotentials, the smaller the substrate channels the higher the specific activity of the electrocatalyst. This is attributed to higher concentrations of protons, relative to bulk solution, required to balance the potential inside the nano-confined channel. However, at higher overpotentials where limitation by mass transport of oxygen becomes important, the nanozymes with larger substrate channels showed higher electrocatalytic activity. A reaction-diffusion model revealed that the higher electrocatalytic activity at low overpotentials with smaller substrate channels can be explained by the higher concentration of protons. The model suggests that the dominant mode of mass transport to achieve these high concentrations is by migration, exemplifying how nano-confinement can be used to enhance reaction rates. Experimental and theoretical data show that under mass transport limiting potentials, the nano-confinement has no effect and the reaction only occurs at the entrance of the substrate channel at the nanoparticle surface. © The Royal Society of Chemistry.

[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.

A universal nano-capillary based method for sample deposition on the silicon nitride membrane of liquid-cell transmission electron microscopy (LCTEM) chips is demonstrated. It is applicable to all substances which can be dispersed in a solvent and are suitable for drop casting, including catalysts, biological samples, and polymers. Most importantly, this method overcomes limitations concerning sample immobilization due to the fragility of the ultra-thin silicon nitride membrane required for electron transmission. Thus, a straightforward way is presented to widen the research area of LCTEM to encompass any sample which can be externally deposited beforehand. Using this method, NixB nanoparticles are deposited on the μm-scale working electrode of the LCTEM chip and in situ observation of single catalyst particles during ethanol oxidation is for the first time successfully monitored by means of TEM movies. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Controlling the formation of nanosized branched nanoparticles with high uniformity is one of the major challenges in synthesizing nanocatalysts with improved activity and stability. Using a cubic-core hexagonal-branch mechanism to form highly monodisperse branched nanoparticles, we vary the length of the nickel branches. Lengthening the nickel branches, with their high coverage of active facets, is shown to improve activity for electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF), as an example for biomass conversion. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Discovering precious metal-free electrocatalysts exhibiting high activity and stability toward both the oxygen reduction (ORR) and the oxygen evolution (OER) reactions remains one of the main challenges for the development of reversible oxygen electrodes in rechargeable metal–air batteries and reversible electrolyzer/fuel cell systems. Herein, a highly active OER catalyst, Fe0.3Ni0.7OX supported on oxygen-functionalized multi-walled carbon nanotubes, is substantially activated into a bifunctional ORR/OER catalyst by means of additional incorporation of MnOX. The carbon nanotube-supported trimetallic (Mn-Ni-Fe) oxide catalyst achieves remarkably low ORR and OER overpotentials with a low reversible ORR/OER overvoltage of only 0.73 V, as well as selective reduction of O2 predominantly to OH−. It is shown by means of rotating disk electrode and rotating ring disk electrode voltammetry that the combination of earth-abundant transition metal oxides leads to strong synergistic interactions modulating catalytic activity. The applicability of the prepared catalyst for reversible ORR/OER electrocatalysis is evaluated by means of a four-electrode configuration cell assembly comprising an integrated two-layer bifunctional ORR/OER electrode system with the individual layers dedicated for the ORR and the OER to prevent deactivation of the ORR activity as commonly observed in single-layer bifunctional ORR/OER electrodes after OER polarization. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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.

Herein, we report the synthesis of a γ-Al2O3-supported NiCo catalyst for dry methane reforming (DMR) and study the catalyst using in situ scanning transmission X-ray microscopy (STXM) during the reduction (activation step) and under reaction conditions. During the reduction process, the NiCo alloy particles undergo elemental segregation with Co migrating toward the center of the catalyst particles and Ni migrating to the outer surfaces. Under DMR conditions, the segregated structure is maintained, thus hinting at the importance of this structure to optimal catalytic functions. Finally, the formation of Ni-rich branches on the surface of the particles is observed during DMR, suggesting that the loss of Ni from the outer shell may play a role in the reduced stability and hence catalyst deactivation. These findings provide insights into the morphological and electronic structural changes that occur in a NiCo-based catalyst during DMR. Further, this study emphasizes the need to study catalysts under operating conditions in order to elucidate material dynamics during the reaction. © 2020 American Chemical Society.

Laser fragmentation in liquids (LFL) allows the synthesis of fully inorganic, ultrasmall gold nanoparticles, usAu NPs (<3 nm). Although the general method is well established, there is a lack of understanding the chemical processes that are triggered by the laser pulses, which may dictate the surface properties that are highly important in heterogeneous oxidation catalytic reactions. We observed the formation of radical oxygen species during LFL, which suggested that LFL is a physicochemical process that leads to particle size reductions and initiates oxidative processes. When the ionic strength in the nanoenvironment was increased, the oxidation of the first atomic layer saturated at 50%, whereby the surface charge density increases continuously. We found a correlation between the surface charge density after synthesis of colloidal nanoparticles and its behavior in catalysis. The properties of the laser-generated nanoparticles in the colloidal state appear to have predetermined the catalytic performance. We found that a smaller surface charge density of the usAu NPs was beneficial for the catalytic activity in CO and ethanol oxidation, while their peroxidase-like activity was affected less. The catalytic activity was 2 times higher for samples prepared by chloride-free LFL after ozone pretreatment compared to samples prepared in pure water. Copyright © 2020 American Chemical Society.

The use of renewable energy by means of electrochemical techniques by converting H2O, CO2 and N2 into chemical energy sources and raw materials, is the basis for securing a future sustainable “green” energy supply. Some weaknesses and inconsistencies in the practice of determining the electrocatalytic performance, which prevents a rational bottom-up catalyst design, are discussed. Large discrepancies in material properties as well as in electrocatalytic activity and stability become obvious when materials are tested under the conditions of their intended use as opposed to the usual laboratory conditions. They advocate for uniform activity/stability correlations under application-relevant conditions, and the need for a clear representation of electrocatalytic performance by contextualization in terms of functional investigation or progress towards application is emphasized. © 2020 The Authors. Published by Wiley-VCH GmbH

In plasma-driven biocatalysis, enzymes are employed to carry out reactions using species generated by non-thermal plasmas as the precursors. We have previously demonstrated that this is feasible in principle, but that the approach suffers from the short lifetime of the biocatalyst under operating conditions. In this work, protection strategies were investigated to prevent the dielectric barrier discharge plasma-induced inactivation of biocatalysts, using recombinant unspecific peroxygenase from Agrocybe aegerita (rAaeUPO), one of the most promising enzymes for plasma-driven biocatalysis. Treatment in oxygen-free atmospheres did not provide any advantage over treatment in synthetic air, indicating that the detrimental reactive species did not originate from oxygen in the plasma phase. Chemical scavengers were employed to eliminate undesired reactive species, without any long-term effect on enzyme lifetime. Similarly, chaperones, including the known stress response proteins Hsp33, CnoX, and RidA did not increase the lifetime of rAaeUPO. Immobilization of the biocatalyst proved effective in preserving enzyme activity. The residual activity of rAaeUPO after plasma treatment strongly depended on the specific immobilization support. Essentially complete protection for at least 15 min of plasma exposure was achieved with an epoxy-butyl-functionalized carrier. This study presents new insights into plasma-protein interactions and plots a path forward for protecting biocatalytic proteins from plasma-mediated inactivation. © 2020 IOP Publishing Ltd.

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.

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.

We mapped the metal sequences within crystals of metal-oxide rods in multivariate metal-organic framework-74 containing mixed combinations of cobalt (Co), cadmium (Cd), lead (Pb), and manganese (Mn). Atom probe tomography of these crystals revealed the presence of heterogeneous spatial sequences of metal ions that we describe, depending on the metal and synthesis temperature used, as random (Co, Cd, 120°C), short duplicates (Co, Cd, 85°C), long duplicates (Co, Pb, 85°C), and insertions (Co, Mn, 85°C). Three crystals were examined for each sequence type, and the molar fraction of Co among all 12 samples was observed to vary from 0.4 to 0.9, without changing the sequence type. Compared with metal oxides, metal-organic frameworks have high tolerance for coexistence of different metal sizes in their rods and therefore assume various metal sequences. © 2020 American Association for the Advancement of Science. All rights reserved.

Binary metal clusters are of high interest for applications in heterogeneous catalysis and have received much attention in recent years. To gain insights into their structure and composition at the atomic scale, computer simulations can provide valuable information if reliable interatomic potentials are available. In this paper we describe the construction of a high-dimensional neural network potential (HDNNP) intended for simulations of large brass nanoparticles with thousands of atoms, which is also applicable to bulk α-brass and its surfaces. The HDNNP, which is based on reference data obtained from density-functional theory calculations, is very accurate with a root-mean-square error of 1.7 meV/atom for total energies and 39 meV Å-1 for the forces of structures not included in the training set. The potential has been thoroughly validated for a wide range of energetic and structural properties of bulk α-brass, its surfaces as well as clusters of different size and composition demonstrating its suitability for large-scale molecular dynamics and Monte Carlo simulations with first-principles accuracy. © 2020 American Chemical Society.

Complex solid-solution electrocatalysts (also referred to as high-entropy alloy) are gaining increasing interest owing to their promising properties which were only recently discovered. With the capability of forming complex single-phase solid solutions from five or more constituents, they offer unique capabilities of fine-tuning adsorption energies. However, the elemental complexity within the crystal structure and its effect on electrocatalytic properties is poorly understood. We discuss how addition or replacement of elements affect the adsorption energy distribution pattern and how this impacts the shape and activity of catalytic response curves. We highlight the implications of these conceptual findings on improved screening of new catalyst configurations and illustrate this strategy based on the discovery and experimental evaluation of several highly active complex solid solution nanoparticle catalysts for the oxygen reduction reaction in alkaline media. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Amorphous silica-aluminas (ASAs) are widely used in acid-catalyzed C-H activation reactions and biomass conversions in large scale, which can be promoted by increasing the strength of surface Brønsted acid sites (BAS). Here, we demonstrate the first observation on a synergistic effect caused by two neighboring Al centers interacting with the same silanol group in flame-made ASAs with high Al content. The two close Al centers decrease the electron density on the silanol oxygen and thereby enhance its acidity, which is comparable to that of dealuminated zeolites, while ASAs with small or moderate Al contents provide mainly moderate acidity, much lower than that of zeolites. The ASAs with enhanced acidity exhibit outstanding performances in C–H bond activation of benzene and glucose dehydration to 5-hydroxymethylfurfural, simultaneously with an excellent calcination stability and resistance to leaching, and they offer an interesting potential for a wide range of acid and multifunctional catalysis. © 2020, The Author(s).

The milling ball is the catalyst. We introduce a palladium-catalyzed reaction inside a ball mill, which makes catalyst powders, ligands, and solvents obsolete. We present a facile and highly sustainable synthesis concept for palladium-catalyzed C−C coupling reactions, exemplarily showcased for the Suzuki polymerization of 4-bromo or 4-iodophenylboronic acid giving poly(para-phenylene). Surprisingly, we observe one of the highest degrees of polymerization (199) reported so far. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

A future widespread application of electrochemical energy conversion and storage technologies strongly depends on the substitution of precious metal-based electrocatalysts for the high-overpotential oxygen reduction and oxygen evolution reactions. We report a novel Co/Co–Fe nanoparticles/N-doped carbon composite electrocatalyst (Co/CoxFey/NC) obtained by pyrolysis of CoFe layered double hydroxide (CoFe LDH) embedded in a film of a bisphenol A and tetraethylenepentamine-based polybenzoxazine poly(BA-tepa). During pyrolysis poly(BA-tepa) forms a highly conductive nitrogen-doped carbon matrix encapsulating Co/Co–Fe nanoparticles, thereby circumventing the need of any additional binder material and conductive additives. Optimization with respect to pyrolysis temperature, the CoFe LDH/BA-tepa ratio, as well as of the gas atmosphere used during the thermal treatment was performed. The optimized Co/CoxFey/NC composite material catalyst exhibits remarkable bifunctional activity towards oxygen reduction (ORR) and oxygen evolution (OER) reactions in 0.1 M KOH represented by a potential difference of only 0.77 V between the potentials at which current densities of −1 mA cm−2 for the ORR and 10 mA cm−2 for the OER were recorded. Moreover, the Co/CoxFey/NC composite material pyrolyzed in ammonia atmosphere exhibits promising stability during both the ORR and the OER. © 2019 Elsevier Ltd

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.

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.

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

Svante Augustus Arrhenius (1859, Vik - 1927, Stockholm) received the Nobel Prize for Chemistry in 1903 “in recognition of the extraordinary services he rendered to the advancement of chemistry by his electrolytic theory of dissociation”. Arrhenius was a physicist, and he received his PhD from the University of Uppsala, where he later became a professor for phyiscal chemistry, the first in the country for this subject. He was offered several positions as professor abroad, but decided to remain in Sweden and to build a Nobel Institute for physical chemistry using the Nobel funds. He remained director of the Institute until his death. There are powerful lessons to take from Svante August Arrhenius’ journey leading to a Nobel laureate as there are from his tremendous contributions to chemistry and science in general, including climate science, immunochemistry and cosmology. The theory of electrolytic dissociation for which Arrhenius received the 1903 Nobel Prize in Chemistry has had a profound impact on our understanding of the chemistry of solutions, chemical reactivity, mechanisms underlying chemical transformations as well as physiological processes. As a tribute to Arrhenius, we present a brief historical perspective and present status of the theory of electrolytic dissociation, its relevance and role to the development of electrochemistry, as well as some perspectives on the possible role of the theory to future advancements in electroanalysis, electrocatalysis and electrochemical energy storage. The review briefly highlights Arrhenius’ contribution to climate science owing to his studies on the potential effects of increased anthropogenic CO2 emissions on the global climate. These studies were far ahead of their time and revealed a daunting global dilemma, global warming, that we are faced with today. Efforts to abate or reverse CO2 accumulation constitute one of the most pressing scientific problems of our time, “man's urgent strive to save self from the adverse effects of his self-orchestrated change on the climate”. Finally, we review the application of the Arrhenius equation that correlates reaction rate constants (k) and temperature (T); (Formula presented.), in determining reaction barriers in catalysis with a particular focus on recent modifications of the equation to account for reactions exhibiting non-linear Arrhenius behavior with concave curvature due to prevalence of quantum mechanical tunneling, as well as infrequent convexity of Arrhenius plots due to decrease of the microcanonical rate coefficient with energy as observed for some enzyme catalyzed reactions. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Iron-sulfur clusters are common building blocks for electron transport and active sites of metalloproteins. Their comprehensive investigation is crucial for understanding these enzymes, which play important roles in modern biomimetic catalysis and biotechnology applications. We address this issue by utilizing (Et4N)3[Fe4Te4(SPh)4], a tellurium modified version of a conventional reduced [4Fe-4S]+ cluster, and performed both 57Fe- and 125Te-NRVS to reveal its characteristic vibrational features. Our analysis exposed major differences in the resulting 57Fe spectrum profile as compared to that of the respective [4Fe-4S] cluster, and between the 57Fe and 125Te profiles. DFT calculations are applied to rationalize structural, electronic, vibrational, and redox-dependent properties of the [4Fe-4Te]+ core. We herein highlight the potential of sulfur/tellurium exchange as a method to isolate the iron-only motion in enzymatic systems. © 2019 The Royal Society of Chemistry.

The impact of individual HAuCl4 nanoreactors is measured electrochemically, which provides operando insights and precise control over the modification of electrodes with functional nanoparticles of well-defined size. Uniformly sized micelles are loaded with a dissolved metal salt. These solution-phase precursor entities are then reduced electrochemically—one by one—to form nanoparticles (NPs). The charge transferred during the reduction of each micelle is measured individually and allows operando sizing of each of the formed nanoparticles. Thus, particles of known number and sizes can be deposited homogenously even on nonplanar electrodes. This is demonstrated for the decoration of cylindrical carbon fibre electrodes with 25±7 nm sized Au particles from HAuCl4-filled micelles. These Au NP-decorated electrodes show great catalyst performance for ORR (oxygen reduction reaction) already at low catalyst loadings. Hence, collisions of individual precursor-filled nanocontainers are presented as a new route to nanoparticle-modified electrodes with high catalyst utilization. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

The reduction in noble metal content for efficient oxygen evolution catalysis is a crucial aspect towards the large scale commercialisation of polymer electrolyte membrane electrolyzers. Since catalytic stability and activity are inversely related, long service lifetime still demands large amounts of low-abundant and expensive iridium. In this manuscript we elaborate on the concept of maximizing the utilisation of iridium for the oxygen evolution reaction. By combining different tin oxide based support materials with liquid atomic layer deposition of iridium oxide, new possibilities are opened up to grow thin layers of iridium oxide with tuneable noble metal amounts. In-situ, time- and potential-resolved dissolution experiments reveal how the stability of the substrate and the catalyst layer thickness directly affect the activity and stability of deposited iridium oxide. Based on our results, we elaborate on strategies how to obtain stable and active catalysts with maximized iridium utilisation for the oxygen evolution reaction and demonstrate how the activity and durability can be tailored correspondingly. Our results highlight the potential of utilizing thin noble metal films with earth abundant support materials for future catalytic applications in the energy sector. [Figure not available: see fulltext.]. © 2019, The author(s).

Due to material gaps and synthesis-related cross-correlations in heterogeneous catalysis, chemists and physicists are constantly motivated to develop novel catalyst preparation methods for independent control of morphology, size, and composition. Within this article, advances, opportunities, and the current limits of laser-based catalyst preparation technique, as well as synergies with conventional methods will be reviewed in terms of purity, particle size, morphology, composition, and nanoparticle-support interaction. It will be shown, that the surfactant-free particles represent ideal model materials to validate kinetic models and conduct parametric activity studies by independent adjustment of functional properties like nanoparticle size, composition, and load. Consequently, the importance of transient plasma dynamics tailoring nanoparticle formation will be pointed out, comparing experimental studies with own calculations and novel simulations taken from literature. Finally, perspectives of surfactant-free colloidal nanoparticles for unrevealing active sites in heterogeneous catalysts are presented. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Coupling electrochemical generation of hydrogen with the concomitant formation of an industrially valuable product at the anode instead of oxygen can balance the high costs usually associated with water electrolysis. We report the synthesis of a variety of nanoparticulate LaCo1−xFexO3 perovskite materials through a specifically optimized spray-flame nanoparticle synthesis method, using different ratios of La, Co, and Fe precursor compounds. Structural characterization of the resulting materials by XRD, TEM, FTIR, and XPS analysis revealed the formation of mainly perovskite-type materials. The electrocatalytic performance of the formed perovskite-type materials towards the oxygen evolution reaction and the ethanol oxidation reaction was investigated by using rotating disk electrode voltammetry. An increased Fe content in the precursor mixture leads to a decrease in the electrocatalytic activity of the nanoparticles. The selectivity towards alcohol oxidation in alkaline media was assessed by using the ethanol oxidation reaction as a model reaction. Operando electrochemistry/ATR-IR spectroscopy results reveal that acetate and acetaldehyde are the final products, depending on the catalyst composition as well as on the applied potential. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Determination of the intrinsic electrocatalytic activity of nanomaterials by means of macroelectrode techniques is compromised by ensemble and film effects. Here, a unique “particle on a stick” approach is used to grow a single metal–organic framework (MOF; ZIF-67) nanoparticle on a nanoelectrode surface which is pyrolyzed to generate a cobalt/nitrogen-doped carbon (CoN/C) composite nanoparticle that exhibits very high catalytic activity towards the oxygen evolution reaction (OER) with a current density of up to 230 mA cm−2 at 1.77 V (vs. RHE), and a high turnover frequency (TOF) of 29.7 s−1 at 540 mV overpotential. Identical location transmission electron microscopy (IL-TEM) analysis substantiates the “self-sacrificial” template nature of the MOF, while post-electrocatalysis studies reveal agglomeration of Co centers within the CoN/C composite during the OER. “Single-entity” electrochemical analysis allows for deriving the intrinsic electrocatalytic activity and furnishes insight into the transient behavior of the electrocatalyst under reaction conditions. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Electrochemical conversion of CO2 to alcohols is one of the most challenging methods of conversion and storage of electrical energy in the form of high-energy fuels. The challenge lies in the catalyst design to enable its real-life implementation. Herein, we demonstrate the synthesis and characterization of a cobalt(III) triphenylphosphine corrole complex, which contains three polyethylene glycol residues attached at the meso-phenyl groups. Electron-donation and therefore reduction of the cobalt from cobalt(III) to cobalt(I) is accompanied by removal of the axial ligand, thus resulting in a square-planar cobalt(I) complex. The cobalt(I) as an electron-rich supernucleophilic d8-configurated metal centre, where two electrons occupy and fill up the antibonding dz 2 orbital. This orbital possesses high affinity towards electrophiles, allowing for such electronically configurated metals reactions with carbon dioxide. Herein, we report the potential dependent heterogeneous electroreduction of CO2 to ethanol or methanol of an immobilized cobalt A3-corrole catalyst system. In moderately acidic aqueous medium (pH = 6.0), the cobalt corrole modified carbon paper electrode exhibits a Faradaic Efficiency (FE%) of 48 % towards ethanol production. © 2019, The Author(s).

The modification of nickel with boron or phosphorus leads to significant enhancement of its electrocatalytic activity for the oxygen evolution reaction (OER). However, the precise role of the guest elements, B and P, in enhancing the OER of the host element (Ni) remains unclear. Herein, we present insight into the role of B and P in enhancing electrocatalysis of oxygen evolution by nickel borides and nickel phosphides. The apparent activation energy, Ea*, of electrocatalytic oxygen evolution on Ni2P was 78.4 kJ/mol, on Ni2B 65.4 kJ/mol, and on Ni nanoparticles 94.0 kJ/mol, thus revealing that both B and P affect the intrinsic activity of nickel. XPS data revealed shifts of −0.30 and 0.40 eV in the binding energy of the Ni 2p3/2 peak of Ni2B and Ni2P, respectively, with respect to that of pure Ni at 852.60 eV, thus indicating that B and P induce opposite electronic effects on the surface electronic structure of Ni. The origin of enhanced activity for oxygen evolution cannot, therefore, be attributed to such electronic modification or ligand effect. Severe changes induced on the nickel lattice, specifically, the Ni-Ni atomic order and interatomic distances (strain effect), by the presence of the guest atoms seem to be the dominant factors responsible for enhanced activity of oxygen evolution in nickel borides and nickel phosphides. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

We present airbrush spray-coating as a reproducible method for the preparation of Mo-doped BiVO4 (Mo : BiVO4) as photoabsorber with different layer thicknesses and Mo content. Optimisation of layer thickness is aiming on diminishing limitations by the electronic conductivity within the photoabsorber, thus increasing the incident photon to current efficiency (IPCE) of the samples. Furthermore, the Mo to V ratio leading to the highest photocurrent density was determined, and the optimised Mo : BiVO4 samples were decorated with a variety of oxygen evolution reaction (OER) electrocatalysts such as cobalt phosphate and layered double hydroxides. A mass loading gradient of Ni−Fe LDH was sprayed on top of the Mo : BiVO4 photoanode for optimisation of the OER catalyst loading. The photocurrent density was enhanced by up to 5.8 times at 0.8 V vs. RHE in comparison with the pristine Mo : BiVO4 sample in absence of any OER electrocatalyst. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

The rapid upsurge of metal–organic frameworks (MOFs) as well as MOF-derived materials has stimulated profound interest to capitalize on their many potential untapped benefits in electrocatalysis for energy applications. The possibility of tuning the metal–ligand junctions of the MOF architecture opens new avenues to design robust, extended heterostructures for addressing the present-day energy challenges. Interestingly, despite having detailed crystallographic information, it is often difficult to envisage the interplay of charge transport (electrons and ions), mass transport (pore system) together with the specific effects of the molecularly defined reaction center of MOFs for a given electrocatalytic reaction. Here, guidelines are offered for judiciously engineering the electronic structure of MOFs to deliver targeted electrocatalytic function. Some of the pivotal works on MOF-based materials for electrocatalysis are discussed, which can be correlated to the biological models in terms of their structural resemblance and an instructive insight is provided about the “new chemistry” that can be explored based on the lessons learned from nature in combination with the theoretical understanding of the energetics of the reactions. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The temporal evolution of photogenerated carriers in CuWO4, CuO and WO3 thin films deposited via a direct chemical vapor deposition approach was studied using time-resolved microwave conductivity and terahertz spectroscopy to obtain the photocarrier lifetime, mobility and diffusion length. The carrier transport properties of the films prepared by varying the copper-to-tungsten stoichiometry were compared and the results related to the performance of the compositions built into respective photoelectrochemical cells. Superior carrier mobility was observed for CuWO4 under frontside illumination. © 2019 Walter de Gruyter GmbH, Berlin/Boston.

Understanding the fundamentals of iridium degradation during the oxygen evolution reaction is of importance for the development of efficient and durable water electrolysis systems. The degradation mechanism is complex and it is under intense discussion whether the oxygen molecule can be directly released from the oxide lattice. Here, we define the extent of lattice oxygen participation in the oxygen evolution and associated degradation of rutile and hydrous iridium oxide catalysts, and correlate this mechanism with the atomic-scale structures of the catalytic surfaces. We combine isotope labelling with atom probe tomography, online electrochemical and inductively coupled plasma mass spectrometry. Our data reveal that, unlike rutile IrO2, Ir hydrous oxide contains -IrIIIOOH species which directly contribute to the oxygen evolution from the lattice. This oxygen evolution mechanism results in faster degradation and dissolution of Ir. In addition, near surface bulk regions of hydrous oxide are involved in the oxygen catalysis and dissolution, while only the topmost atomic layers of rutile IrO2 participate in both reactions. Overall our data provide a contribution to the fundamental understanding of the exceptional stability of Ir-oxides towards the oxygen evolution reaction. The proposed approach to a quantitative assessment of the degree of lattice oxygen participation in the oxygen evolution reaction can be further applied to other oxide catalyst systems. © 2019 The Royal Society of Chemistry.

Catalysis often requires spatial separation of active centres. In material science this translates to a challenge in the synthesis of such materials, namely core-shells. Yolk-shell materials, a type of core-shell materials, possess a void between the core and shell that can be advantageous in catalysis. Yolk-shell materials with zeolitic core have not been reported extensively, despite their potential applicability in catalysis. This stems from the non-spherical morphology and surface properties of the zeolites, which makes controlled coating without defects difficult. Herein, we report a strategy for the encapsulation of beta zeolite (HBEA) with disordered mesoporous silica shell (HBEA@void@mSiO 2 ). HBEA is chosen as the centre (yolk) due to its cuboidal shape. The process involves creation of two shells, (a) sacrificial shell composed of resorcinol and formaldehyde, and (b) mesoporous silica shell. The result is an organic@inorganic hybrid that is thermally treated to obtain the corresponding hybrid. Polyvinylpyrrolidone (PVP) is an important component of the synthesis which assists in obtaining a uniform coating around the core. Thorough morphological, structural, fractal and textural characterization of this material was performed by electron microscopy, XRD, SAXS and sorption techniques. The hybrid possesses a hierarchical structure with an increasing porosity and spatial isolation of the core by the presence of a void. The siliceous nature of HBEA@void@mSiO 2 also enables a post-synthesis treatment for functional modification with mercaptosilane groups. The synthesis process shown here is highly controllable and has laid a solid foundation for a generalized synthesis strategy to build functional yolk-shell materials based on zeolites. © 2019

A biohybrid photobioanode mimicking the Z-scheme has been developed by functional integration of photosystem II (PSII) and PbS quantum dots (QDs) within an inverse opal TiO2 architecture giving rise to a rather negative water oxidation potential of about −0.55 V vs. Ag/AgCl, 1 m KCl at neutral pH. The electrical linkage between both light-sensitive entities has been established through an Os-complex-modified redox polymer (POs), which allows the formation of a multi-step electron-transfer chain under illumination starting with the photo-activated water oxidation at PSII followed by an electron transfer from PSII through POs to the photo-excited QDs and finally to the TiO2 electrode. The photobioanode was coupled to a novel, transparent, inverse-opal ATO cathode modified with an O2-reducing bilirubin oxidase for the construction of a H2O/O2 photobioelectrochemical cell reaching a high open-circuit voltage of about 1 V under illumination. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

A biohybrid photobioanode mimicking the Z-scheme has been developed by functional integration of photosystem II (PSII) and PbS quantum dots (QDs) within an inverse opal TiO 2 architecture giving rise to a rather negative water oxidation potential of about −0.55 V vs. Ag/AgCl, 1 m KCl at neutral pH. The electrical linkage between both light-sensitive entities has been established through an Os-complex-modified redox polymer (P Os ), which allows the formation of a multi-step electron-transfer chain under illumination starting with the photo-activated water oxidation at PSII followed by an electron transfer from PSII through P Os to the photo-excited QDs and finally to the TiO 2 electrode. The photobioanode was coupled to a novel, transparent, inverse-opal ATO cathode modified with an O 2 -reducing bilirubin oxidase for the construction of a H 2 O/O 2 photobioelectrochemical cell reaching a high open-circuit voltage of about 1 V under illumination. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Complex solid solution (CSS) nanoparticles were recently discovered as efficient electrocatalysts for a variety of reactions. As one of many advantages, they exhibit the potential to replace noble-metal catalysts with multinary combinations of transition metals because they offer formation of new unique and tailorable active sites of multiple elements located next to each other. This Perspective reports on the current state and on challenges of the (combinatorial) synthesis of multinary nanoparticles and advanced electron microscopy characterization techniques for revealing structure-activity correlations on an atomic scale. We discuss what distinguishes this material class from common catalysts to highlight their potential to act as electrocatalysts and rationalize their nontypical electrochemical behavior. We provide an overview about challenges in synthesis, characterization, and electrochemical evaluation and propose guidelines for future design of CSS catalysts to achieve further progress in this research field, which is still in its infancy. © 2019 American Chemical Society.

We evaluated electrochemical degradation (ECD) and photocatalytic degradation (PCD) technologies for saline water purification, with a focus on rate comparison and formation and degradation of chlorinated aromatic intermediates using the same non-chlorinated parent compound, 4-ethylphenol (4EP). At 15 mA·cm-2, and in the absence of chloride (0.6 mol·L-1 NaNO3 was used as supporting electrolyte), ECD resulted in an apparent zero-order rate of 30 μmol L-1·h-1, whereas rates of ∼300 μmol L-1·h-1 and ∼3750 μmol L-1·h-1 were computed for low (0.03 mol·L-1) and high (0.6 mol·L-1) NaCl concentration, respectively. For PCD, initial rates of ∼330 μmol L-1·h-1 and 205 μmol L-1·h-1 were found for low and high NaCl concentrations, at a photocatalyst (TiO2) concentration of 0.5 g·L-1, and illumination at λmax ≈ 375 nm, with an intensity ∼0.32 mW·cm-2. In the chlorine mediated ECD approach, significant quantities of free chlorine (hypochlorite, Cl2) and chlorinated hydrocarbons were formed in solution, while photocatalytic degradation did not show the formation of free chlorine, nor chlorine-containing intermediates, and resulted in better removal of non-purgeable hydrocarbons than ECD. The origin of the minimal formation of free chlorine and chlorinated compounds in photocatalytic degradation is discussed based on photoelectrochemical results and existing literature, and explained by a chloride-mediated surface-charge recombination mechanism. © 2019 American Chemical Society.

The development of bifunctional oxygen electrodes is a key factor for the envisaged application of rechargeable metal-air batteries. In this work, we present a simple procedure based on pyrolysis of polybenzoxazine/metal metalloid nanoparticles composites into efficient bifunctional oxygen reduction and oxygen evolution electrocatalysts. This procedure generates nitrogen-doped carbon with embedded metal metalloid nanoparticles exhibiting high activity towards both, oxygen reduction and oxygen evolution, in 0.1 M KOH with a roundtrip voltage of as low as 0.81 V. Koutecký-Levich analysis coupled with scanning electrochemical microscopy reveals that oxygen is preferentially reduced in a 4e− transfer pathway to hydroxide rather than to hydrogen peroxide. Furthermore, the polybenzoxazine derived carbon matrix allows for stable catalyst fixation on the electrode surface, resulting in unattenuated activity during continuous alternate polarisation between oxygen evolution at 10 mA cm−2 and oxygen reduction at −1.0 mA cm−2. © 2018 Elsevier Ltd

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.

Supported catalysts are among the most important classes of catalysts. They are typically prepared by wet-chemical methods, such as impregnation or co-precipitation. Here we disclose that dry ball milling of macroscopic metal powder in the presence of a support oxide leads in many cases to supported catalysts with particles in the nanometer size range. Various supports, including TiO2, Al2O3, Fe2O3, and Co3O4, and different metals, such as Au, Pt, Ag, Cu, and Ni, were studied, and for each of the supports and the metals, highly dispersed nanoparticles on supports could be prepared. The supported catalysts were tested in CO oxidation, where they showed activities in the same range as conventionally prepared catalysts. The method thus provides a simple and cost-effective alternative to the conventionally used impregnation methods. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

“Single entity” measurements are central for an improved understanding of the function of nanoparticle-based electrocatalysts without interference arising from mass transfer limitations and local changes of educt concentration or the pH value. We report a scanning electrochemical cell microscopy (SECCM) investigation of zeolitic imidazolate framework (ZIF-67)-derived Co−N-doped C composite particles with respect to the oxygen evolution reaction (OER). Surmounting the surface wetting issues as well as the potential drift through the use of a non-interfering Os complex as free-diffusing internal redox potential standard, SECCM could be successfully applied in alkaline media. SECCM mapping reveals activity differences relative to the number of particles in the wetted area of the droplet landing zone. The turnover frequency (TOF) is 0.25 to 1.5 s−1 at potentials between 1.7 and 1.8 V vs. RHE, respectively, based on the number of Co atoms in each particle. Consistent values at locations with varying number of particles demonstrates OER performance devoid of macroscopic film effects. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

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.

We studied the photocatalytic aerobic oxidation of HCl over TiO2 for producing Cl2. Steady-state Cl2 production rates were determined with a photocatalytic fixed-bed gas-phase reactor equipped with UV light-emitting diodes (LEDs) using iodometric titration as online analytics. We found stable Cl2 production rates of up to 16 mmol h−1 m−2 for commercial anatase TiO2 Hombikat UV100. The rate increased linearly with temperature from 21 to 140 °C, indicating the acceleration of the limiting desorption rate of the coupled product water. Comparing different TiO2 polymorphs revealed that anatase possesses higher activity than rutile. The adsorption of HCl was monitored in situ by IR spectroscopy. The IR spectra indicated that HCl chemisorption chlorinates the surface of TiO2 under the reaction conditions, suggesting it to be the first step of the reaction mechanism. High stability opens up the opportunity of developing a promising photocatalytic process of HCl recycling at lower temperatures suitable for reaching full conversion. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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).

NiFe layered double hydroxide (LDH) is inarguably the most active contemporary catalyst for the oxygen evolution reaction under alkaline conditions. However, the ability to sustain unattenuated performance under challenging industrial conditions entailing high corrosivity of the electrolyte (≈30 wt. % KOH), high temperature (>80 °C) and high current densities (>500 mA cm−2) is the ultimate criterion for practical viability. This work evaluates the chemical and structural stability of NiFe LDH at conditions akin to practical electrolysis, in 30 % KOH at 80 °C, however, without electrochemical polarization, and the resulting impact on the OER performance of the catalyst. Post-analysis of the catalyst by means of XRD, TEM, FT-IR, and Raman spectroscopy after its immersion into 7.5 m KOH at 80 °C for 60 h revealed a transformation of the structure from NiFe LDH to a mixture of crystalline β-Ni(OH)2 and discrete predominantly amorphous FeOOH containing minor non-homogeneously distributed crystalline domains. These structural and compositional changes led to a drastic loss of the OER activity. It is therefore recommended to study catalyst stability at industrially relevant conditions. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

The determination of the intrinsic properties of nanomaterials is essential for their optimization as electrocatalysts, however it poses great challenges from the standpoint of analytical tools and methods. Herein, we report a novel methodology that allows for a binder-free investigation of electrocatalyst nanoparticles. The potential-assisted immobilization of a non-noble metal catalyst, i.e., nickel-iron layered double hydroxide (NiFe LDH) nanoparticles, was employed to directly attach small nanoparticle ensembles from a suspension to the surface of etched carbon nanoelectrodes. The dimensions of this type of electrodes allowed for the immobilization of the catalyst material below the picogram scale and resulted in a high resolution towards the faradaic current response. In addition the effect of the electrochemical aging on the intrinsic activity of the catalyst was investigated in alkaline media by means of continuous cyclic voltammetry. A change in the material properties could be observed, which was accompanied by a substantial decrease in its intrinsic activity. [Figure not available: see fulltext.] © 2018, Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature.

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.

Surface-enhanced Raman spectroscopy is a powerful analytical tool and a strongly surface structure-dependent process. Importantly, it can be coupled with electrochemistry to simultaneously record vibrational spectroscopic information during electrocatalytic reactions. Highest Raman enhancements are obtained using precisely tuned nanostructures. The fabrication and evaluation of a high number of different nanostructures with slightly different properties is time-consuming. We present a strategy to systematically determine optimal nanostructure properties of electrochemically generated Ag void structures in order to find the void size providing highest signal enhancement for Raman spectroscopy. Ag-coated Si wafers were decorated with a monolayer of differently sized polymer nanospheres using a Langmuir-Blodgett approach. Subsequently, bipolar electrochemistry was used to electrodeposit a gradient of differently sized void structures. The gradient structures were locally evaluated using Raman spectroscopy of a surface-adsorbed Raman probe, and the surface regions exhibiting the highest Raman enhancement were characterized by means of scanning electron microscopy. High-throughput scanning droplet cell experiments were utilized to determine suitable conditions for the electrodeposition of the found highly active structure in a three-electrode electrochemical cell. This structure was subsequently employed as the working electrode in operando surface-enhanced Raman measurements to verify its viability as the signal amplifier and to spectroscopically rationalize the complex electrochemical reduction of carbon dioxide. © 2018 American Chemical Society.

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).

Materials used for photocatalytic overall water splitting (POWS) are typically composed of light-absorbing semiconductor crystals, functionalized with so-called cocatalytic nanoparticles to improve the kinetics of the hydrogen and/or oxygen evolution reactions. While function, quantity, and protection of such metal(oxide) nanoparticles have been addressed in the literature of photocatalysis, the stability and transients in the active oxidation-state upon illumination have received relatively little attention. In this Perspective, the latest insights in the active state of frequently applied cocatalysts systems, including Pt, Rh/Cr2O3, or Ni/NiOx, will be presented. While the initial morphology and oxidation state of such nanoparticles is a strong function of the applied preparation procedure, significant changes in these properties can occur during water splitting. We discuss these changes in relation to the nature of the cocatalyst/semiconductor interface. We also show how know-how of other disciplines such as heterogeneous catalysis or electro-catalysis and recent advances in analytical methodology can help to determine the active state of cocatalytic nanoparticles in photocatalytic applications. © 2018 American Chemical Society.

Achieving stability with highly active Ru nanoparticles for electrocatalysis is a major challenge for the oxygen evolution reaction. As improved stability of Ru catalysts has been shown for bulk surfaces with low-index facets, there is an opportunity to incorporate these stable facets into Ru nanoparticles. Now, a new solution synthesis is presented in which hexagonal close-packed structured Ru is grown on Au to form nanoparticles with 3D branches. Exposing low-index facets on these 3D branches creates stable reaction kinetics to achieve high activity and the highest stability observed for Ru nanoparticle oxygen evolution reaction catalysts. These design principles provide a synthetic strategy to achieve stable and active electrocatalysts. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Pd or Pt alloyed with a secondary metal are the typical catalysts at the anode for the direct oxidation of methanol. The secondary metal is employed to diminish deactivation commonly ascribed to CO poisoning. Here we investigate the origin of the improved performance of Au-Pd core-shell and alloy nanocrystals as electrocatalysts for the methanol oxidation reaction (MOR), relative to Pd alone. Monodisperse Au-Pd core-shell nanocrystals were synthesized using H2 as a mild reducing agent followed by annealing under a 5% H2 atmosphere to produce the Au-Pd alloys. The nanocrystals were characterized using high-resolution electron microscopy to confirm their structures. The core-shell and alloy nanocrystals showed an improvement in specific activity with respect to pure Pd nanocrystals. Importantly, the stability was also improved by the inclusion of Au for both nanocrystals, being 2.7× higher for the alloy than for the core-shell after 30 min, while the activity is completely lost for the Pd nanocrystals within 10 min. We show that there is no evidence of CO formation for any of the Pd-based catalysts in an alkaline environment. The origin of the improvement in terms of both activity and stability results from positive shifts in the PdO formation/reduction potential caused by the presence of Au, which results in more Pd sites available for the MOR. © 2018 American Chemical Society.

The transformation of CO2 into fuels and chemicals by photocatalysis is a promising strategy to provide a long-term solution to mitigating global warming and energy-supply problems. Achievements in photocatalysis during the last decade have sparked increased interest in using sunlight to reduce CO2. Traditional semiconductors used in photocatalysis (e.g. TiO2) are not suitable for use in natural sunlight and their performance is not sufficient even under UV irradiation. Some two-dimensional (2D) materials have recently been designed for the catalytic reduction of CO2. These materials still require significant modification, which is a challenge when designing a photocatalytic process. An overarching aim of this Review is to summarize the literature on the photocatalytic conversion of CO2 by various 2D materials in the liquid phase, with special attention given to the development of novel 2D photocatalyst materials to provide a basis for improved materials. © 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

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.

Despite the availability of numerous electroanalytical methods for phosphate quantification, practical implementation in point-of-use sensing remains virtually nonexistent because of interferences from sample matrices or from atmospheric O2. In this work, phosphate determination is achieved by the purine nucleoside phosphorylase (PNP) catalyzed reaction of inosine and phosphate to produce hypoxanthine which is subsequently oxidized by xanthine oxidase (XOx), first to xanthine and then to uric acid. Both PNP and XOx are integrated in a redox active Os-complex modified polymer, which not only acts as supporting matrix for the bienzymatic system but also shuttles electrons from the hypoxanthine oxidation reaction to the electrode. The bienzymatic cascade in this second generation phosphate biosensor selectively delivers four electrons for each phosphate molecule present. We introduced an additional electrochemical process involving uric acid oxidation at the underlying electrode. This further enhances the anodic current (signal amplification) by two additional electrons per analyte molecule which mitigates the influence of electrochemical interferences from the sample matrix. Moreover, while the XOx catalyzed reaction is sensitive to O2, the uric acid production and therefore the delivery of electrons through the subsequent electrochemical process are independent of the presence of O2. Consequently, the electrochemical process counterbalances the O2 interferences, especially at low phosphate concentrations. Importantly, the electrochemical uric acid oxidation specifically reports on phosphate concentration since it originates from the product of the bienzymatic reactions. These advantageous properties make this bioelectrochemical-electrochemical cascade particularly promising for point-of-use phosphate measurements. © 2018 Elsevier B.V.

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).

2D layered materials, including metal-di-chalcogenides and transition metal layered double hydroxides, among others, are intensively studied because of new properties that emerge from their 2D confinement, which are attractive for advanced applications. Herein, 2D cobalt ion (Co2+) and benzimidazole (bIm) based zeolite-imidazole framework nanosheets, ZIF-9(III), are reported as exceptionally efficient electrocatalysts for the oxygen evolution reaction (OER). Specifically, liquid-phase ultrasonication is applied to exfoliate a [Co4(bIm)16] zeolite-imidazole framework (ZIF), named as ZIF-9(III) phase, into nanoscale sheets. ZIF-9(III) is selectively prepared through simple mechanical grinding of cobalt nitrate and benzimidazole in the presence of a small amount of ethanol. The resultant exfoliated nanosheets exhibit significantly higher OER activity in alkaline conditions than the corresponding bulk phases ZIF-9 and ZIF-9(III). The electrochemical and physicochemical characterization data support the assignment of the OER activity of the exfoliated nanosheet derived material to nitrogen coordinated cobalt oxyhydroxide N4CoOOH sites, following a mechanism known for Co-porphyrin and related systems. Thus, exfoliated 2D nanosheets hold promise as potential alternatives to commercial noble metal electrocatalysts for the OER. © 2018 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The topmost atomic layers of electrocatalysts determine the mechanism and kinetics of reactions in many important industrial processes, such as water splitting, chlor-electrolysis or fuel cells. Optimizing the performance of electrocatalysts requires a detailed understanding of surface-state changes during the catalytic process, ideally at the atomic scale. Here, we use atom probe tomography to reveal the three-dimensional structure of the first few atomic layers of electrochemically grown iridium oxide, an efficient electrocatalyst for the oxygen evolution reaction. We unveil the formation of confined, non-stoichiometric Ir-O species during oxygen evolution. These species gradually transform to IrO2, providing improved stability but also a decrease in activity. Additionally, electrochemical growth of oxide in deuterated solutions allowed us to trace hydroxy-groups and water molecules present in the regions of the oxide layer that are favourable for the oxygen evolution and iridium dissolution reactions. Overall, we demonstrate how tomography with near-atomic resolution advances the understanding of complex relationships between surface structure, surface state and function in electrocatalysis. © 2018 The Author(s).

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

An improved general understanding of electrocatalytic gas evolution reactions may - besides contributing to fundamental knowledge - play a crucial role in efforts directed to energy savings during large-scale industrial electrocatalytic processes. Aside from the search for new electrocatalytically active materials, in-depth understanding of electrode surface properties may contribute to more efficient utilization of known electrocatalysts. SECM is applied in the sample generation/tip collection mode to determine the spatial distribution of electrocatalytic activity during Cl2 evolution at the solid/liquid interface of dimensionally stable anodes. Statistical interpretation of the local microscopic distribution of the electrocatalytic activity of dimensionally stable anodes was used as a basis for improved understanding of their overall electrocatalytic performance. © 2018

The electrochemical oxidation of the biorefinery product 5-(hydroxymethyl)furfural (HMF) to 2,5-furandicarboxylic acid (FDCA), an important platform chemical for the polymer industry, is receiving increasing interest. FDCA-based polymers such as polyethylene 2,5-furandicarboxylate (PEF) are sustainable candidates for replacing polyethylene terephthalate (PET). Herein, we report the highly efficient electrocatalytic oxidation of HMF to FDCA, using Ni foam modified with high-surface-area nickel boride (NixB) as the electrode. Constant potential electrolysis in combination with HPLC revealed a high faradaic efficiency of close to 100 % towards the production of FDCA with a yield of 98.5 %. Operando electrochemistry coupled to ATR-IR spectroscopy indicated that HMF is oxidized preferentially via 5-hydroxymethyl-2-furancarboxylic acid rather than via 2,5-diformylfuran, which is in agreement with HPLC results. This study not only reports a low-cost active electrocatalyst material for the electrochemical oxidation of HMF to FDCA, but additionally provides insight into the reaction pathway. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Enzymes are characterized by an active site that is typically embedded deeply within the protein shell thus creating a nanoconfined reaction volume in which high turnover rates occur. We propose nanoparticles with etched substrate channels as a simplified enzyme mimic, denominated nanozymes, for electrocatalysis. We demonstrate increased electrocatalytic activity for the oxygen reduction reaction using PtNi nanoparticles with isolated substrate channels. The PtNi nanoparticles comprise an oleylamine capping layer that blocks the external surface of the nanoparticles participating in the catalytic reaction. Oxygen reduction mainly occurs within the etched channels providing a nanoconfined reaction volume different from the bulk electrolyte conditions. The oxygen reduction reaction activity normalized by the electrochemically active surface area is enhanced by a factor of 3.3 for the nanozymes compared to the unetched nanoparticles and a factor of 2.1 compared to mesoporous PtNi nanoparticles that possess interconnecting pores. © Copyright 2018 American Chemical Society.

Rapid motion of electrolyte ions is a crucial requirement to ensure the fast charging/discharging and the high power densities of supercapacitor devices. This motion is primarily determined by the pore size and connectivity of the used porous carbon electrodes. Here, the diffusion characteristics of each individual electrolyte component, that is, anion, cation, and solvent confined to model carbons with uniform and well-defined pore sizes are quantified. As a result, the contributions of micropores, mesopores, and hierarchical pore architectures to the overall transport of adsorbed mobile species are rationalized. Unexpectedly, it is observed that the presence of a network of mesopores, in addition to smaller micropores—the concept widely used in heterogeneous catalysis to promote diffusion of sorbates—does not necessarily enhance ionic transport in carbon materials. The observed phenomenon is explained by the stripping off the surrounding solvent shell from the electrolyte ions entering the micropores of the hierarchical material, and the resulting enrichment of solvent molecules preferably in the mesopores. It is believed that the presented findings serve to provide fundamental understanding of the mechanisms of electrolyte diffusion in carbon materials and depict a quantitative platform for the future designing of supercapacitor electrodes on a rational basis. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

There are certainly many more pitfalls in analyzing and reporting catalysis work, but based on our experience, the points above represent a large majority of the technical flaws in manuscripts submitted to Chemistry of Materials in the field of catalysis. Proper reporting according to the advice above will reduce the frustration of editors, reviewers and authors, leading to a more streamlined publishing experience. © 2018 American Chemical Society.

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

In the endeavor of discovering new noble metal–free electrocatalysts for the oxygen reduction reaction, noble metal–free multinary transition metal nanoparticle libraries are investigated. The complexity of such multiple principal element alloys provides access to a large variety of different elemental compositions, each with potentially unique properties. The strategy for efficient identification of novel electrocatalytically active systems comprises combinatorial co-sputtering into an ionic liquid followed by potential-assisted immobilization of the formed nanoparticles at a microelectrode which allows the evaluation of their intrinsic electrocatalytic activity in alkaline media. A surprisingly high intrinsic activity is found for the system Cr–Mn–Fe–Co–Ni, which is at least comparable to Pt under the same conditions, an unexpected result based on the typical properties of its constituents. Systematic removal of each element from the quinary alloy system yields a significant drop in activity for all quaternary alloys, indicating the importance of the synergistic combination of all five elements, likely due to formation of a single solid solution phase with altered properties which enables the limitations of the single elements to be overcome. Multinary transition metal alloys as a novel material class in electrocatalysis with basically unlimited possibilities for catalyst design, targeting the replacement of noble metal–based materials, are suggested. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

A nanocomposite of ZnV 2 O 6 with hierarchical flower-like structure hybridized with reduced graphene oxide (rGO) was fabricated using a facile hydrothermal approach. The structure, morphology, optical and electronic properties were explored using comprehensive analytical techniques. The results revealed that the rGO sheets were decorated with the in situ-formed ZnV 2 O 6 nanoparticles yielding a well-combined composite structure. The photocatalytic activity of as-prepared ZnV 2 O 6 /rGO hybrids is 2.48 times larger than that of pristine ZnV 2 O 6 for the degradation of Rhodamine B (RhB). In parallel to the experimental results, the basic mechanisms of interfacial interaction, charge transfer/separation and subsequently their influence on the photocatalytic activity were theoretically studied by first-principles calculations. The photocatalytic enhancement is attributed to efficient interfacial electron transfer from ZnV 2 O 6 to rGO, leading to a prolonged lifetime of photoinduced charge carriers. We anticipate that these results will lead to new insights in the judicious design of graphene-based semiconductor photocatalysts. © 2018 The Electrochemical Society.

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.

In this study, evidence is provided that isolated surface vanadia (VO4) species on SiO2 can similarly act as a thermal heterogeneous catalyst and as a heterogeneous photocatalyst. Structurally identical surface VO4 species catalyze the selective oxidation of methanol both by thermal activation and by UV-light induction. Selectivity to formaldehyde appears to be unity. For the photocatalytic reaction at room temperature, formaldehyde desorption is rate limiting. With larger agglomerates or V2O5 nanoparticles, on the contrary, only the thermal reaction is feasible. This is tentatively attributed to the different positions of electronic states (HOMO/LUMO, valence/conduction band) on the electrochemical energy scale owing to the quantum size effect. Besides providing new fundamental insight into the mode of action of nanosized photocatalysts, our results demonstrate that tuning the photocatalytic reactivity of supported transition-metal oxides by adjusting the degree of agglomeration is feasible. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

[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

Solid-liquid interfaces play an important role in many fields like electrochemistry, corrosion, and heterogeneous catalysis. For understanding the related processes, detailed insights into the elementary steps at the atomic level are mandatory. Here we unravel the properties of prototypical surface-defects like adatoms and vacancies at a number of copper-water interfaces including the low-index Cu(111), Cu(100), and Cu(110), as well as the stepped Cu(211) and Cu(311) surfaces. Using a first-principles quality neural network potential constructed from density functional theory reference data in combination with molecular dynamics and metadynamics simulations, we investigate the defect diffusion mechanisms and the associated free energy barriers. Further, the solvent structure and the mobility of the interfacial water molecules close to the defects are analyzed and compared to the defect-free surfaces. We find that, like at the copper-vacuum interface, hopping mechanisms are preferred compared to exchange mechanisms, while the associated barriers for hopping are reduced in the presence of liquid water. The water structure close to adatoms and vacancies exhibits pronounced local features and differs strongly from the structure at the ideal low-index surfaces. Moreover, in particular at Cu(111) the adatoms are very mobile and hopping events along the surface are more frequent than the exchange of coordinating water molecules in their local environment. Consequently, adatom self-diffusion processes at Cu(111) involve entities of adatoms and their associated solvation shells. © 2017 American Chemical Society.

The German Catalysis Society (GeCatS) is the platform for the entire German catalysis community both in basic and applied research with about 1100 members from industry and academia. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

A simple and efficient hydrodeoxygenation strategy is described to selectively generate and separate high-value alkylphenols from pyrolysis bio-oil, produced directly from lignocellulosic biomass. The overall process is efficient and only requires low pressures of hydrogen gas (5 bar). Initially, an investigation using model compounds indicates that MoCx/C is a promising catalyst for targeted hydrodeoxygenation, enabling selective retention of the desired Ar−OH substituents. By applying this procedure to pyrolysis bio-oil, the primary products (phenol/4-alkylphenols and hydrocarbons) are easily separable from each other by short-path column chromatography, serving as potential valuable feedstocks for industry. The strategy requires no prior fractionation of the lignocellulosic biomass, no further synthetic steps, and no input of additional (e.g., petrochemical) platform molecules. © 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

Glycerol is a major by-product of the biodiesel production and is therefore produced in high quantities. While currently there are limited possible applications for this highly functionalized molecule, glycerol can be a cheap and abundant feedstock for value-added products that are accessible by selective oxidation. Usually, the selective oxidation of glycerol utilizes expensive noble metal catalysts, such as Au, Pt, and Pd. Here we report the selective oxidation of glycerol in basic media, using ordered mesoporous Cu-Al2O3 catalysts with various Cu loadings prepared by a facile soft-templating method. The materials were characterized in detail by nitrogen physisorption, vis-NIR spectroscopy, EDX, low- and wide-angle XRD, XPS, and TEM. Subsequently the reaction conditions for glycerol oxidation were optimized. The catalytic oxidation of glycerol yields C3 products, such as glyceric acid and tartronic acid, and also C2 and C1 products, such as glycolic acid, oxalic acid, and formic acid. Moreover, the role of the solvent on the catalytic reaction was investigated, and the addition of various co-solvents to the aqueous reaction mixture was found to increase the initial reaction rate up to a factor of three. The trends of the initial reaction rates correlate well with the polarity of the water/co-solvent mixtures. The prepared Cu-Al2O3 catalysts are a more cost-efficient and environmentally viable alternative to the reported noble metal catalysts. © 2017 The Royal Society of Chemistry.

Tandem catalysis is an attractive strategy to intensify chemical technologies. However, simultaneous control over the individual and concerted catalyst performances poses a challenge. We demonstrate that enhanced pore transport within a Co/Al2O3 Fischer–Tropsch (FT) catalyst with hierarchical porosity enables its tandem integration with a Pt/ZSM-5 zeolitic hydrotreating catalyst in a spatially distant fashion that allows for catalyst-specific temperature adjustment. Nevertheless, this system resembles the case of close active-site proximity by mitigating secondary reactions of primary FT α-olefin products. This approach enables the combination of in situ dewaxing with a minimum production of gaseous hydrocarbons (18 wt %) and an up to twofold higher (50 wt %) selectivity to middle distillates compared to tandem pairs based on benchmark mesoporous FT catalysts. An overall 80 % selectivity to liquid hydrocarbons from syngas is attained in one step, attesting to the potential of this strategy for increasing the carbon efficiency in intensified gas-to-liquid technologies. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Developing high-performance non-precious metal catalysts (NPMCs) for the oxygen-reduction reaction (ORR) is of critical importance for sustainable energy conversion. We report a novel NPMC consisting of iron carbide (Fe3C) nanoparticles encapsulated in N-doped bamboo-like carbon nanotubes (b-NCNTs), synthesized by a new metal-organic framework (MOF)-templated assembly approach. The electrocatalyst exhibits excellent ORR activity in 0.1m KOH (0.89V at -1mAcm-2) and in 0.5m H2SO4 (0.73V at -1mAcm-2) with a hydrogen peroxide yield of below 1% in both electrolytes. Due to encapsulation of the Fe3C nanoparticles inside porous b-NCNTs, the reported NPMC retains its high ORR activity after around 70hours in both alkaline and acidic media. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Co-based layered double hydroxide (LDH) catalysts with Fe and Al contents in the range of 15 to 45 at % were synthesized by an efficient coprecipitation method. In these catalysts, Fe3+ or Al3+ ions play an essential role as trivalent species to stabilize the LDH structure. The obtained catalysts were characterized by a comprehensive combination of surface- and bulk-sensitive techniques and were evaluated for the oxygen evolution reaction (OER) on rotating disk electrodes. The OER activity decreased upon increasing the Al content for the Co- and Al-based LDH catalysts, whereas a synergistic effect in Co- and Fe-based LDHs was observed, which resulted in an optimal Fe content of 35 at %. This catalyst was spray-coated on Ni foam electrodes and showed very good stability in a flow-through cell with a potential of approximately 1.53 V at 10 mA cm−2 in 1 m KOH for at least 48 h. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Prompted by the impact of Ni-based support materials on the intrinsic activity of electrocatalysts, we investigated the influence of partial Co substitution by Ni during the reductive thermal synthesis of cobalt-cobalt phosphide nanoparticles from triphenylphosphine complexes. The obtained catalysts were characterised by X-ray diffraction and electrochemistry. Increasing the amount of Ni in the precursor complexes leads to materials with lower overpotential for the OER at low current densities, and lower Tafel slopes. Co nanoparticles, which are only formed in materials with low Ni content, increase the intrinsic material conductivity and reduce the OER overpotential at high current densities. © 2017

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.

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.

Engineering stable electrodes using highly active catalyst nanopowders for electrochemical water splitting remains a challenge. We report an innovative and general approach for attaining highly stable catalyst films with self-healing capability based on the in situ self-assembly of catalyst particles during electrolysis. The catalyst particles are added to the electrolyte forming a suspension that is pumped through the electrolyzer. Particles with negatively charged surfaces stick onto the anode, while particles with positively charged surfaces stick to the cathode. The self-assembled catalyst films have self-healing properties as long as sufficient catalyst particles are present in the electrolyte. The proof-of-concept was demonstrated in a non-zero gap alkaline electrolyzer using NiFe-LDH and NixB catalyst nanopowders for anode and cathode, respectively. Steady cell voltages were maintained for at least three weeks during continuous electrolysis at 50–100 mA cm−2. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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.

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

In addition to catalytic activity, intrinsic stability, tight immobilization on a suitable electrode surface, and sufficient electronic conductivity are fundamental prerequisites for the long-term operation of particle- and especially powder-based electrocatalysts. We present a novel approach to concurrently address these challenges by using the unique properties of polybenzoxazine (pBO) polymers, namely near-zero shrinkage and high residual-char yield even after pyrolysis at high temperatures. Pyrolysis of a nanocubic prussian blue analogue precursor (KmMnx[Co(CN)6]y⋅n H2O) embedded in a bisphenol A and aniline-based pBO led to the formation of a N-doped carbon matrix modified with MnxCoyOz nanocubes. The obtained electrocatalyst exhibits high efficiency toward the oxygen evolution reaction (OER) and more importantly a stable performance for at least 65 h. © 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.

Chemical vapor synthesis (CVS) is a unique method to prepare well-defined photocatalyst materials with both large specific surface area and a high degree of crystallinity. The obtained β-Ga2O3 nanoparticles were optimized for photocatalysis by reductive photodeposition of the Rh/CrOx co-catalyst system. The influence of the degree of crystallinity and the specific surface area on photocatalytic aqueous methanol reforming and overall water splitting (OWS) was investigated by synthesizing β-Ga2O3 samples in the temperature range from 1000 °C to 1500 °C. With increasing temperature, the specific surface area and the microstrain were found to decrease, whereas the degree of crystallinity and the crystallite size increased. Whereas the photocatalyst with the highest specific surface area showed the highest aqueous methanol reforming activity, the highest OWS activity was that for the sample with an optimum ratio between high degree of crystallinity and specific surface area. Thus, it was possible to show that the facile aqueous methanol reforming and the demanding OWS have different requirements for high photocatalytic activity. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

As part of an ongoing effort to understand the deactivation and improve the stability of metal oxide-supported Au catalysts in the low-temperature CO oxidation reaction while maintaining their high activity, we have investigated the influence of a mesoporous silica SBA-15 substrate on the activity and stability of Au/TiO2 catalysts, which consist of a SBA-15 support surface modified by a monolayer of TiOx with Au nanoparticles on top. The extent of the TiOx surface modification was systematically increased, while the Au loading and the Au particle sizes were largely kept constant. Employing kinetic measurements at three different temperatures (30 °C, 80 °C, 180 °C) and a number of ex situ methods as well as in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) for catalyst characterization, we found that the activity of these catalysts increases significantly with the Ti concentration and with reaction temperature. The tendency for deactivation remains essentially unchanged. Detailed in situ DRIFTS measurements reveal that the Au nanoparticles are largely formed on the TiOx surface-modified areas of the SBA-15 support and that the tendency for surface carbonate formation is very low. The observed deactivation may at least partly be related to the accumulation of molecularly adsorbed H2O species, in particular at low temperatures (30 °C). These are likely to be formed from surface hydroxyl groups, they may affect the reaction either by blocking of active sites or by blocking the adsorption of reactants on the substrate. Other effects, such as reaction induced changes in the titania layer, must however, play a role as well, both at 80 °C and in particular at 180 °C, where accumulation of adsorbed species is negligible. The mechanistic ideas are supported by reactivation tests subsequent to calcination at 400 °C, which were found to fully restore the initial activity. © 2017 Elsevier Inc.

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

In situ ball milling of solid catalysts is a promising yet almost unexplored concept for boosting catalytic performance. The continuous preferential oxidation of CO (CO-PROX) under in situ ball milling of Cu-based catalysts such as Cu/Cr2O3 is presented. At temperatures as low as −40 °C, considerable activity and more than 95 % selectivity were achieved. A negative apparent activation energy was observed, which is attributed to the mechanically induced generation and subsequent thermal healing of short-lived surface defects. In situ ball milling at sub-zero temperatures resulted in an increase of the CO oxidation rate by roughly 4 orders of magnitude. This drastic and highly selective enhancement of CO oxidation showcases the potential of in situ ball milling in heterogeneous catalysis. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

We report metallic NiPS3@NiOOH core shell heterostructures as an efficient and durable electrocatalyst for the oxygen evolution reaction, exhibiting a low onset potential of 1.48 V (vs RHE) and stable performance for over 160 h. The atomically thin NiPS3 nanosheets are obtained by exfoliation of bulk NiPS3 in the presence of an ionic surfactant. The OER mechanism was studied by a combination of SECM, in situ Raman spectroscopy, SEM, and XPS measurements, which enabled direct observation of the formation of a NiPS3@NiOOH core shell heterostructure at the electrode interface. Hence, the active form of the catalyst is represented as NiPS3@NiOOH core shell structure. Moreover, DFT calculations indicate an intrinsic metallic character of the NiPS3 nanosheets with densities of states (DOS) similar to the bulk material. The high OER activity of the NiPS3 nanosheets is attributed to a high density of accessible active metallic-edge and defect sites due to structural disorder, a unique NiPS3@NiOOH core shell heterostructure, where the presence of P and S modulates the rface electronic structure of Ni in NiPS3, thus providing excellent conductive pathway for efficient electron-transport to the NiOOH shell. These findings suggest that good size control during liquid exfoliation may be advantageously used for the formation of electrically conductive NiPS3@ NiOOH core shell electrode materials for the electrochemical water oxidation.

High sensitivity and high spatial resolution in localized electrochemical measurements are the key advantages of electroanalysis using nanometer-sized electrodes. Due to recent progress in nanoelectrode fabrication and electrochemical instrument development, nanoelectrochemical methods are becoming more widespread. We summarize different protocols for the fabrication of needle-type nanoelectrodes and discuss their properties with regard to various applications. We discuss the limits of conventional theory to describe electrochemistry at the nanoscale and point out technical aspects for characterization and handling of nanometric electrodes. Different applications are highlighted: i) Nanoelectrodes are powerful tools for non-ensemble studies of electrocatalysis at single nanoparticles at high mass transport rates. ii) Electrochemical nanosensors are employed for highly localized non-invasive analysis of single living cells and intracellular detection of neurotransmitters and metabolites. iii) Used in scanning electrochemical probe techniques, nanoprobes afford topographical and truly chemical imaging of samples with high spatial resolution. © 2016 Published by Elsevier B.V.

Individual Ni(OH)2 nanoparticles deposited on carbon nanoelectrodes are investigated in non-ensemble measurements with respect to their energy storage properties and electrocatalysis for the oxygen evolution reaction (OER). Charging by oxidation of Ni(OH)2 is limited by the diffusion of protons into the particle bulk and the OER activity is independent of the particle size. © 2016 The Royal Society of Chemistry.

Many different aerogel materials are known to be accessible via the controlled destabilization of the respective nanoparticle suspensions. Especially for applications in heterogeneous catalysis such materials with high specific surface areas are highly desirable. Here, a facile method to obtain a mixed ZnPd/ZnO aerogel via a reductive treatment of a preformed Pd/ZnO aerogel is presented. Different morphologies of the Pd/ZnO aerogels could be achieved by controlling the destabilization of the ZnO sol. All aerogels show a high CO2 selectivity of up to 96% and a very good activity in methanol steam reforming that delivers hydrogen, which is one of the most important fuels for future energy concepts. The method presented is promising for different transition metal/metal oxide systems and hence opens a path to a huge variety of materials. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

By employing the mixed-component, solid-solution approach, various functionalized ditopic isophthalate (ip) defect-generating linkers denoted 5-X-ipH2, where X=OH (1), H (2), NH2(3), Br (4), were introduced into the mixed-valent ruthenium analogue of [Cu3(btc)2]n(HKUST-1, btc=benzene-1,3,5-tricarboxylate) to yield Ru-DEMOFs (defect-engineered metal–organic frameworks) of the general empirical formula [Ru3(btc)2−x(5-X-ip)xYy]n. Framework incorporation of 5-X-ip was confirmed by powder XRD, FTIR spectroscopy, ultrahigh-vacuum IR spectroscopy, thermogravimetric analysis,1H NMR spectroscopy, N2sorption, and X-ray absorption near edge structure. Interestingly, Ru-DEMOF 1 c with 32 % framework incorporation of 5-OH-ip shows the highest BET surface area (≈1300 m2g−1, N2adsorption, 77 K) among all materials (including the parent framework [Ru3(btc)2Yy]n). The characterization data are consistent with two kinds of structural defects induced by framework incorporation of 5-X-ip: modified paddlewheel nodes featuring reduced ruthenium sites (Ruδ+, 0< δ< 2, type A) and missing nodes leading to enhanced porosity (type B). Their relative abundances depend on the choice of the functional group X in the defect linkers. Defects A and B also appeared to play a key role in sorption of small molecules (i.e., CO2, CO, H2) and the catalytic properties of the materials (i.e., ethylene dimerization and the Paal–Knorr reaction). © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Nanocasting is a general and widely applied method in the generation of porous materials during which a sacrificial solid template is used as a mold on the nanoscale. Ideally, the resulting structure is the inverse of the template. However, replication is not always as direct as anticipated, so the influences of the degree of pore filling and of potential restructuring processes after removal of the template need to be considered. These apparent limitations give rise to opportunities in the synthesis of poly(styrene-co-divinylbenzene) (PSD) polymer networks of widely varying porosities (BET surface area=63–562 m2g−1; Vtot=0.18–1.05 cm3g−1) by applying a single synthesis methodology. In addition, spatially selective sulfonation on the nanoscale seems possible. Together, nanocasting and sulfonation enable rational catalyst design. The highly porous nanocast and predominantly surface-sulfonated PSD networks approach the activity of the corresponding molecular catalyst, para-toluenesulfonic acid, and exceed those of commercial ion-exchange polymers in the depolymerization of macromolecular inulin. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Developing electrocatalysts with low cost, high activity, and good durability is urgently demanded for the wide commercialization of fuel cells. By taking advantage of nanostructure engineering, we fabricated PtAg nanotubular aerogels (NTAGs) with high electrocatalytic activity and good durability via a simple galvanic replacement reaction between the in situ spontaneously gelated Ag hydrogel and the Pt precursor. The PtAg NTAGs have hierarchical porous network features with primary networks and pores from the interconnected nanotubes of the aerogel and secondary networks and pores from the interconnected thin nanowires on the nanotube surface, and they show very high porosities and large specific surface areas. Due to the unique structure, the PtAg NTAGs exhibit greatly enhanced electrocatalytic activity toward formic acid oxidation, reaching 19 times higher metal-based mass current density as compared to the commercial Pt black. Furthermore, the PtAg NTAGs show outstanding structural stability and electrochemical durability during the electrocatalysis. Noble metal-based NTAGs are promising candidates for applications in electrocatalysis not only for fuel cells, but also for other energy-related systems. © 2016 American Chemical Society.

Catalysis is at the core of almost every established and emerging chemical process and also plays a central role in the quest for novel technologies for the sustainable production and conversion of energy. Particularly since the early 2000s, a great surge of interest exists in the design and application of micro- and nanometer-sized materials with hollow interiors as solid catalysts. This review provides an updated and critical survey of the ever-expanding material architectures and applications of hollow structures in all branches of catalysis, including bio-, electro-, and photocatalysis. First, the main synthesis strategies toward hollow materials are succinctly summarized, with emphasis on the (regioselective) incorporation of various types of catalytic functionalities within their different subunits. The principles underlying the scientific and technological interest in hollow materials as solid catalysts, or catalyst carriers, are then comprehensively reviewed. Aspects covered include the stabilization of catalysts by encapsulation, the introduction of molecular sieving or stimuli-responsive "auxiliary" functionalities, as well as the single-particle, spatial compartmentalization of various catalytic functions to create multifunctional (bio)catalysts. Examples are also given on the applications which hollow structures find in the emerging fields of electro- and photocatalysis, particularly in the context of the sustainable production of chemical energy carriers. Finally, a critical perspective is provided on the plausible evolution lines for this thriving scientific field, as well as the main practical challenges relevant to the reproducible and scalable synthesis and utilization of hollow micro- and nanostructures as solid catalysts. © 2016 American Chemical Society.

To accelerate the large-scale commercialization of electrochemical energy storage and conversion technologies through water splitting and regeneration in reversible fuel cells, cost-effective, highly efficient, and durable reversible oxygen electrodes are required. We report a comparatively simple approach to modify a group of oxygen-evolving perovskites based on lanthanum cobaltite into effective bifunctional systems through partial atom substitution, which, upon intermixing with nitrogen-doped carbon nanotubes, achieve remarkably low round-trip overvoltage of <850mV in the electrocatalysis of oxygen reduction and oxygen evolution in an alkaline electrolyte, KOH (0.1m). Besides the bifunctional electrocatalytic performance, the composite systems with a low Fe content possessed promising long-term stability. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dry reforming of methane (DRM) has been studied for many years as an attractive option to produce synthesis gas. However, catalyst deactivation by coking over nonprecious-metal catalysts still remains unresolved. Here, we study the influence of structural and compositional properties of nickel catalysts on the catalytic performance and coking propensity in the DRM. A series of bulk catalysts with different Ni contents was synthesized by calcination of hydrotalcite-like precursors NixMg0.67-xAl0.33(OH)2(CO3)0.17·mH2O prepared by constant-pH coprecipitation. The obtained Ni/MgAl oxide catalysts contain Ni nanoparticles with diameters between 7 and 20 nm. High-resolution transmission electron microscopy (HR-TEM) revealed a nickel aluminate overgrowth on the Ni particles, which could be confirmed by Fourier transform infrared (FTIR) spectroscopy. In particular, catalysts with low Ni contents (5 mol %) exhibit predominantly oxidic surfaces dominated by Ni2+ and additionally some isolated Ni0 sites. These properties, which are determined by the overgrowth, effectively diminish the formation of coke during the DRM, while the activity is preserved. A large (TEM) and dynamic (microcalorimetry) metallic Ni surface at high Ni contents (50 mol %) causes significant coke formation during the DRM. © 2016 American Chemical Society.

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.

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.

N4-macrocyclic complexes are among the most widely investigated molecular materials for the oxygen reduction reaction (ORR). These complexes are attractive because they inherently provide well-defined structural models for describing the ORR not only in nature, for example, in cytochrome c oxidases, but also for electrocatalysts of industrial importance. The development of more efficient N4-macrocyclic complexes as electrocatalysts for the ORR requires in-depth understanding of the most crucial properties that govern their functionality. This goal necessitates employing advanced techniques and methods to accurately probe electrocatalytic behavior. This chapter covers a brief introduction of scanning electrochemical microscopy (SECM) and discusses its application for evaluation of the electrocatalytic behavior of materials, with particular focus on the ORR. A general overview of the benefits of using SECM as an alternative or as a complimentary technique to rotating-ring disk electrode (RRDE) voltammetry in studying the kinetics of the ORR is provided, with examples of this application dedicated to catalysts derived from MN4-macrocyclic complexes. The chapter also covers examples of the application of SECM as a semi-combinatorial and high-throughput tool for catalyst screening and development, and the evaluation of electrocatalysts at temperatures of industrial relevance. Discussion of some recent developments of the application of SECM, or SECM coupled to other auxiliary techniques, in electrocatalysis, for example, in probing electrolysis of individual nanoparticles, and a forecast of its potential future applications in both fundamental and applied science are included at the end of this chapter. © Springer International Publishing Switzerland 2016.

The selectivity of heterogeneously catalyzed chemical reactions is well-known to be dependent on nanoscale determinants, such as surface atomic geometry and composition. However, principles to control the selectivity of nanoparticle (NP) catalysts by means of mesoscopic descriptors, such as the interparticle distance, have remained largely unexplored. We used well-defined copper catalysts to deconvolute the effect of NP size and distance on product selectivity during CO2 electroreduction. Corroborated by reaction-diffusion modeling, our results reveal that mesoscale phenomena such as interparticle reactant diffusion and readsorption of intermediates play a defining role in product selectivity. More importantly, this study uncovers general principles of tailoring NP activity and selectivity by carefully engineering size and distance. These principles provide guidance for the rational design of mesoscopic catalyst architectures in order to enhance the production of desired reaction products. © 2015 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.

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.

Nitrogen-functionalized carbon nanotubes are promising materials in catalysis due to their versatile surface properties involving nitrogen groups, oxygen groups, surface defects and metal impurities. These factors can be used to tune the dispersion, morphology, crystal structure, electronic structure, mobility/stability and finally the catalytic performance of supported metal nanoparticles. This review focuses on selected examples aiming at understanding the interactions between surface groups, defects, and metal species and their impact on the catalytic properties in electrocatalysis and gas-phase redox catalysis. © 2016 The Royal Society of Chemistry.

Nature's subtle systems drive essential reactions responsible for sustenance of our existence “reactions of life” through sophisticated mechanisms of charge transfer, energy harvest and conversion. The interconnectedness between living nature and technologically relevant electrochemical reactions, for example, oxygen reduction and evolution catalyzed by cytochrome c oxidases and photosystem II respectively, and hydrogen oxidation and evolution catalyzed by hydrogenases, does not only intrigue but also inspires us. To what extent therefore can our present understanding of electrocatalysis guide us to decipher nature's sophistication, or rather, can bioinspired electrocatalysis succeed to replicate and supersede nature's perfection “the exemplar paragon”? Herein, we present a harmonized perspective of the principle factors which govern electrocatalysis and bioelectrocatalysis featuring examples of technologically important electrochemical reactions catalyzed by both enzymes and inorganic electrocatalysts. Sound knowledge of the inter-relationships linking electrocatalysis and bioelectrocatalysis is essential for enabling a deeper understanding of nature's bioelectrochemical reactions, and for insightful design of functional catalysts inspired by models from living nature. © 2016 Elsevier Ltd

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.

The (1 1 1)-layered perovskite material Ba5Ta4O15 represents a suitable photoabsorber with remarkable photocatalytic activity in overall water splitting. We are the first to demonstrate overall water splitting without the presence of a noble-metal-based co-catalyst over this catalyst. The photocatalytic activity of Ba5Ta4O15 was investigated by overall water splitting after reductive photodeposition of amorphous Cr2O3. The formation of Cr2O3 nanoparticles for water splitting was evidenced by X-ray photoelectron spectroscopy and transmission electron microscopy. The reductive photodeposition of very low amounts of Cr2O3 on Ba5Ta4O15 induces stable rates in overall water splitting up to 465 μmol h-1 H2 and 228 μmol h-1 O2. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Oxide materials are among the state-of-the-art heterogeneous electrocatalysts for many important large-scale industrial processes, including O2 and Cl2 evolution reactions. However, benchmarking their performance is challenging in many cases, especially at high current densities, which are relevant for industrial applications. Serious complications arise particularly due to (i) the formation of a nonconducting gas phase which blocks the surface during the reactions, (ii) problems in determination of the real electroactive electrode area, and (iii) the large influence of surface morphology alterations (stability issues) under reaction conditions, among others. In this work, an approach overcoming many of these challenges is presented, with a focus on electrochemically formed thin-film oxide electrocatalysts. The approach is based on benefits provided by the use of microelectrodes, and it gives comprehensive information about the surface roughness, catalyst activity, and stability. The key advantages of the proposed method are the possibility of characterization of the whole microelectrode surface by means of atomic force microscopy and an accurate assessment of the specific activity (and subsequently stability) of the catalyst, even at very high current densities. Electrochemically deposited CoOx thin films have been used in this study as model catalysts. © 2016 American Chemical Society.

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

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

Combining advantages of homogeneous and heterogeneous catalysis by incorporating active species on a solid support is often an effective strategy for improving overall catalyst performance, although the influences of the support are generally challenging to establish, especially at a molecular level. Here, we report the local compositions, and structures of platinum species incorporated into covalent triazine framework (Pt-CTF) materials, a solid analogue of the molecular Periana catalyst, Pt(bpym)Cl2, both of which are active for the selective oxidation of methane in the presence of concentrated sulfuric acid. By using a combination of solid-state 195Pt nuclear magnetic resonance (NMR) spectroscopy, aberration-corrected scanning transmission electron microscopy (AC-STEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS), important similarities and differences are observed between the Pt-CTF and Periana catalysts, which are likely related to their respective macroscopic reaction properties. In particular, wide-line solid-state 195Pt NMR spectra enable direct measurement, identification, and quantification of distinct platinum species in as-synthesized and used Pt-CTF catalysts. The results indicate that locally ordered and disordered Pt sites are present in as-synthesized Pt-CTF, with the former being similar to one of the two crystallographically distinct Pt sites in crystalline Pt(bpym)Cl2. A distribution of relatively disordered Pt moieties is also present in the used catalyst, among which are the principal active sites. Similarly XAS shows good agreement between the measured data of Pt-CTF and a theoretical model based on Pt(bpym)Cl2. Analyses of the absorption spectra of Pt-CTF used for methane oxidation suggests ligand exchange, as predicted for the molecular catalyst. XPS analyses of Pt(bpym)Cl2, Pt-CTF, as well as the unmodified ligands, further corroborate platinum coordination by pyridinic N atoms. Aberration-corrected high-angle annular dark-field STEM proves that Pt atoms are distributed within Pt-CTF before and after catalysis. The overall results establish the close similarities of Pt-CTF and the molecular Periana catalyst Pt(bpym)Cl2, along with differences that account for their respective properties. (Figure Presented). © 2016 American Chemical Society.

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.

We propose a method for the formation of highly active bifunctional oxygen electrocatalysts, by exploiting the unique features of nitrogen-rich metallo-macrocyclic complexes and the structural and electronic properties of few-layer graphene. The precursors of the electrocatalysts were synthesized by sonication of graphite in DMF leading to exfoliation and the formation of few-layer graphene sheets in the presence of a suitable transition metal macrocyclic complex. After pyrolysis and subsequent mild calcination metal oxide nanoparticles as well as metal-nitrogen (MNx) moieties embedded within a N-doped graphitic carbon matrix are obtained. The formation, in-depth characterization and electrochemical performance of two different catalysts derived from Co and Ni containing precursor complexes are demonstrated. © 2016 Elsevier Ltd

MAXNET Energy is an initiative of the Max Planck society in which eight Max Planck institutes and two external partner institutions form a research consortium aiming at a deeper understanding of the electrocatalytic conversion of small molecules. We give an overview of the activities within the MAXNET Energy research consortium. The main focus of research is the electrocatalytic water splitting reaction with an emphasis on the anodic oxygen evolution reaction (OER). Activities span a broad range from creation of novel catalysts by means of chemical or material synthesis, characterization and analysis applying innovative electrochemical techniques, atomistic simulations of state-of-the-art x-ray spectroscopy up to model-based systems analysis of coupled reaction and transport mechanisms. Synergy between the partners in the consortium is generated by two modes of cooperation - one in which instrumentation, techniques and expertise are shared, and one in which common standard materials and test protocols are used jointly for optimal comparability of results and to direct further development. We outline the special structure of the research consortium, give an overview of its members and their expertise and review recent scientific achievements in materials science as well as chemical and physical analysis and techniques. Due to the extreme conditions a catalyst has to endure in the OER, a central requirement for a good oxygen evolution catalyst is not only its activity, but even more so its high stability. Hence, besides detailed degradation studies, a central feature of MAXNET Energy is a standardized test setup/protocol for catalyst stability, which we propose in this contribution. ©2015 by De Gruyter Mouton.

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.

The onset potential of an electrocatalytic reaction is frequently used as an indicator to compare the catalytic performance of electrocatalysts. However, in addition to the fact that the onset potential is an undefined physico-chemical value which is dependent on the sensitivity of the used potentiostat its determination using voltammetry at the catalyst-modified electrode surface may be superimposed by additional Faradaic reactions e.g. from redox conversions of the catalyst material or corrosion processes. Gas-evolving electrodes suffer additionally from the dynamics of gas bubble formation and departure leading to inherent limitations of voltammetric studies directly performed at the catalyst-modified electrode. Nanometer-sized electrodes accurately positioned by means of shearforce-based constant-distance mode SECM are proposed for the highly sensitive determination of the onset potential of microcavity electrodes filled with different perovskites as oxygen evolution catalysts. Double barrel microcavity electrodes are additionally suggested for the simultaneous investigation of two catalysts. They enable direct referencing of a catalyst with a benchmark catalyst material in a single experiment. © 2015 Elsevier Ltd. All rights reserved.

In recent years, the field of catalysis has experienced an astonishing transformation, driven in part by more demanding environmental standards and critical societal and industrial needs such as the search for alternative energy sources. Thanks to the advent of nanotechnology, major steps have been made towards the rational design of novel catalysts. Striking new catalytic properties, including greatly enhanced reactivities and selectivities, have been reported for nanoparticle (NP) catalysts as compared to their bulk counterparts. However, in order to harness the power of these nanocatalysts, a detailed understanding of the origin of their enhanced performance is needed. The present review focuses on the role of the NP size and shape on chemisorption and catalytic performance. Since homogeneity in NP size and shape is a prerequisite for the understanding of structure-reactivity correlations, we first review different synthesis methods that result in narrow NP size distributions and shape controlled NPs. Next, size-dependent phenomena which influence the chemical reactivity of NPs, including quantum size-effects and the presence of under-coordinated surface atoms are examined. The effect of the NP shape on catalytic performance is discussed and explained based on the existence of different atomic structures on the NP surface with distinct chemisorption properties. The influence of additional factors, such as the oxidation state of the NPs and NP-support interactions, is also considered in the frame of the size- and shape-dependency that these phenomena present. Ultimately, our review highlights the importance of achieving a systematic understanding of the factors that control the activity and selectivity of a catalyst in order to avoid trial and error methods in the rational design of the new generation of nanocatalysts with properties tunable at the atomic level. © 2015 Elsevier B.V. All rights reserved.

Density functional theory (DFT) has been performed to characterize the structural stability and Lewis acidic properties of the T-COE-4 zeolites, in which the linked site between the layers is isomorphously substituted by the tetravalent Ti-, Sn-, or Zr- heteroatom. The effects of substitution energy and equilibrium geometry parameters on the stability of T-COE-4 are investigated. The computed Fukui function values and the adsorption of ammonia, pyridine, water and trimethylphosphine oxide molecules have been employed to predict the Lewis acid strength of the T-COE-4 zeolites. It is found that the smaller the O1-T-O2 bond angle is, the more difficult is to form the regular tetrahedral unit. The substitution energies at the linker position increase in the following sequence: Ti-COE-4 < Sn-COE-4 < Zr-COE-4. The incorporation of Ti-, Sn-, or Zr-heteroatom enhances the Lewis acidity of COE-4 zeolite. It is predicted that the Lewis acid strength increases in the order of Ti-COE-4 < Zr-COE-4 & Sn-COE-4 by the adsorption of different base molecules. Six O-T-O bond angles are divided into different extent to form the analogous trigonal bipyramid structures in the optimized ligand adsorbed complexes. These findings could be beneficial for the structural design and catalytic function modification of the interlayer-expanded zeolites. © 2015 Elsevier Inc. All rights reserved.

A variety of Os-complex modified redox polymers were synthesized and optimized for an improved bioelectrochemical communication with PQQ-sGDH. The properties of the polymers were varied by changing the monomers composition leading to improved immobilization and increased enzyme loading. Three Os-complexes were designed exhibiting different ligands but similar redox potentials adapted for efficient electron transfer with PQQ-sGDH. Effects of the ligand sphere, polymer backbone and length of the tether chain between Os-complex and polymer backbone as well as the impact of different bifunctional crosslinkers on the catalytic current were evaluated. The optimized bioelectrodes exhibited significantly improved catalytic currents and stability. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Powder catalysts were deposited as thin films on transparent conductive oxides (TCO) by means of an airbrush spray coating technique. Photoelectrocatalytic properties of the powder catalysts were characterized using photocurrent spectroscopy at different wavelengths demonstrating on the one hand the stability of the films and on the other hand the electrical connection with the electrode surface. The morphology and thickness of the deposited powder catalyst films on TCO were characterized using scanning electron microscopy. Aiming at photocatalytic water splitting, semiconductor powders like gallium oxide (Ga2O3) and zinc oxide (ZnO) were used as test samples to optimize the deposition technique resulting in thin homogeneous layers and good adhesion on the conductive substrate. The proposed airbrush deposition technique of powder catalysts allows closing an experimental gap between microheterogeneous systems and modified electrodes for finding suitable materials for photoelectrochemical water splitting. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Highly sensitive and efficient biosensors play a crucial role in clinical, environmental, industrial, and agricultural applications, and tremendous efforts have been dedicated to advanced electrode materials with superior electrochemical activities and low cost. Here, we report a three-dimensional binder-free Cu foam-supported Cu2O nanothorn array electrode developed via facile electrochemistry. The nanothorns growing in situ along the specific direction of <011> have single crystalline features and a mesoporous surface. When being used as a potential biosensor for nonenzyme glucose detection, the hybrid electrode exhibits multistage linear detection ranges with ultrahigh sensitivities (maximum of 97.9 mA mM-1 cm-2) and an ultralow detection limit of 5 nM. Furthermore, the electrode presents outstanding selectivity and stability toward glucose detection. The distinguished performances endow this novel electrode with powerful reliability for analyzing human serum samples. These unprecedented sensing characteristics could be ascribed to the synergistic action of superior electrochemical catalytic activity of nanothorn arrays with dramatically enhanced surface area and intimate contact between the active material (Cu2O) and current collector (Cu foam), concurrently supplying good conductivity for electron/ion transport during glucose biosensing. Significantly, our findings could guide the fabrication of new metal oxide nanostructures with well-organized morphologies and unique properties as well as low materials cost. © 2015 American Chemical Society.

A synergetic interplay: Catalysis is a key research field within BASF. Successful industrial chemistry is always the result of a combination of catalyst and process development. The interplay of catalyst chemistry and reaction engineering is discussed for processes such as the sulfuric acid production, ammonia synthesis, methanol synthesis, fluid catalytic cracking, and direct epoxidation of propylene. (Figure Presented). © 2015 Wiley-VCH Verlag GmbH & Co. KGaA.

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.

Mechanocatalytic depolymerization of lignocellulose constitutes a new frontier in biorefining. In a one-pot process, the combination of mechanical forces and acid catalysis leads to the full conversion of (dried) lignocellulose into water-soluble products (oligosaccharides and lignin fragments). In solution, these products undergo hydrolysis and other reactions, rendering high yields of monosaccharides along with precipitation of a sulfur-free lignin. Therefore, the water-soluble oligosaccharides may serve as a unique replacement for glucose and xylose for the production of platform chemicals. In this work, we report the results obtained from mechanocatalytic depolymerization of α-cellulose, beechwood, and poplar wood performed in Simoloyer mills operating on hectogram and kilogram scales. Irrespective of the process scale, full conversion of the substrate into "water-soluble (ligno)celluloses", within milling durations of 1-3 h, is achieved. A phenomenological analysis of parameters for the process upscaling is provided. Moreover, the energy consumption of the process on different scales is assessed. Remarkably, energy consumption significantly decreases (from ca. 200 MWh·t-1 to 9.6 MWh·t-1) with upscaling of the experiment from 1 g (planetary mill) to 1 kg. This increase in energy efficiency constitutes key evidence for the feasibility of the mechanocatalytic depolymerization on a large scale. © 2015 American Chemical Society.

Better understanding of the factors responsible for the long-term stability of electrocatalysts is of increasing importance for the development of new generations of efficient electrode materials relevant for sustainable energy provision. Therefore, experiments with model, often single-crystal catalytic surfaces are of significance for fundamental electrochemistry and technological applications. Among model electrocatalysts, near-surface alloys (NSAs) of Pt with Cu, Ni and other metals formed via electrochemical deposition and thermal annealing have shown remarkable properties, demonstrating high activity towards a number of important reactions, including the oxygen reduction reaction (ORR) and CO oxidation. However, relatively little is known about the electrochemical stability and mechanisms of degradation of model NSAs. In this work, we employ a simple electrochemical approach, supported by density functional theory calculations, to evaluate the stability of Cu-Pt(111) NSAs in 0.1 M HClO4. Our results show that ∼30% of the Cu atoms initially incorporated into the second atomic layer of Pt are lost within the first 2000 cycles performed between 0.05 V and 1.0 V (RHE). After 5000 cycles, ca. half of the Cu atoms initially placed in the second atomic layer still remained in the subsurface region. The dissolution of Cu has a substantial impact on the measured shift in the average OH-binding energy for the catalyst surface and, consequently, on the ORR activity. Interestingly, after dissolution of Cu from NSAs, voltammetric features, which are characteristic to the Pt(111) facets, are partially restored suggesting the formation of NSA and Pt(111) domains in the resulting surface. © 2015 Elsevier Ltd. All rights reserved.

The notion of metal-free catalysts is used to refer to carbon materials modified with nonmetallic elements. However, some claimed metal-free catalysts are prepared using metal-containing precursors. It is highly contested that metal residues in nitrogen-doped carbon (NC) catalysts play a crucial role in the oxygen reduction reaction (ORR). In an attempt to reconcile divergent views, a definition for truly metal-free catalysts is proposed and the differences between NC and M-Nx/C catalysts are discussed. Metal impurities at levels usually undetectable by techniques such as XPS, XRD, and EDX significantly promote the ORR. Poisoning tests to mask the metal ions reveal the involvement of metal residues as active sites or as modifiers of the electronic structure of the active sites in NC. The unique merits of both M-Nx/C and NC catalysts are discussed to inspire the development of more advanced nonprecious-metal catalysts for the ORR. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

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

With the high interest in improving the performance of electrocatalysts for technologically significant reactions, great efforts are directed at the assessment of the activities of various catalytic materials. For this purpose, it is important to compare the catalytic activities measured using different methods and under different conditions. To achieve this, it is of utmost importance to avoid certain methodological and instrumental issues that can severely affect the obtained experimental results. Using well-defined systems, we demonstrate the importance of experimental conditions in the assessment and benchmarking of the activity of catalytic processes for various reactions. Particularly, we demonstrate that the correction of the uncompensated ohmic resistance using impedance spectroscopy measurements requires particular attention and additional procedures which are normally ignored. Additionally, we demonstrate how the uncompensated resistance changes with the potential if a non-conducting gas phase is accumulated in the system, hence influencing the activity measurement. It is further shown that a correct choice for surface-limited reactions for the determination of the real surface area of catalytic electrodes plays a key role in ensuring more meaningful activity assessment. Not as easy as it seems: Benchmarking of the electrocatalytic activity can be unexpectedly very demanding due to experimental issues which are often underestimated. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

Silica-supported catalysts for the conversion of ethanol to 1,3-butadiene were investigated. The combination of Hf(IV) and Zn(II) resulted in a stable, active, and selective catalyst in which the Zn(II) effectively suppressed the dehydration activity of Hf(IV); the catalyst preparation method plays a crucial role. Using the crystalline Zn-silicate hemimorphite as an alternative Zn(II) source proved to be even more successful in suppressing ethanol dehydration. © 2015 American Chemical Society.

A versatile synthetic procedure to prepare hollow mesoporous carbon spheres (HMCS) is presented here. This approach is based on the deposition of a homogeneous hybrid polymer/silica composite shell on the outer surface of silica spheres through the surfactant-assisted simultaneous polycondensation of silica and polymer precursors in a colloidal suspension. Such composite materials can be further processed to give hollow mesoporous carbon spheres. The flexibility of this method allows for independent control of the morphological (i.e., core diameter and shell thickness) and textural features of the carbon spheres. In particular, it is demonstrated that the size of the pores within the mesoporous shell can be precisely tailored over an extended range (2-20 nm) by simply adjusting the reaction conditions. In a similar fashion, also the specific carbon surface area as well as the total shell porosity can be tuned. Most importantly, the textural features can be adjusted without affecting the dimension or the morphology of the spheres. The possibility to directly modify the shell textural properties by varying the synthetic parameters in a scalable process represents a distinct asset over the multistep hard-templating (nanocasting) routes. As an exemplary application, Pt nanoparticles were encapsulated in the mesoporous shell of HMCS. The resulting Pt@HMCS catalyst showed an enhanced stability during the oxygen reduction reaction, one of the most important reactions in electrocatalysis. This new synthetic procedure could allow the expansion, perhaps even beyond the lab-scale, of advanced carbon nanostructured supports for applications in catalysis. © 2015 American Chemical Society.

Co3O4 with a spinel structure is a very active oxide catalyst for the oxidation of CO. In such catalysts, octahedrally coordinated Co3+ is considered to be the active site, while tetrahedrally coordinated Co2+ is assumed to be basically inactive. In this study, a highly ordered mesoporous CoO has been prepared by H2 reduction of nanocast Co3O4 at low temperature (250 °C). The as-prepared CoO material, which has a rock-salt structure with a single Co2+ octahedrally coordinated by lattice oxygen in Fm3¯m symmetry, exhibited unexpectedly high activity for CO oxidation. Careful investigation of the catalytic behavior of mesoporous CoO catalyst led to the conclusion that the oxidation of surface Co2+ to Co3+ causes the high activity. Other mesoporous spinels (CuCo2O4, CoCr2O4, and CoFe2O4) with different Co species substituted with non/low-active metal ions were also synthesized to investigate the catalytically active site of cobalt-based catalysts. The results show that not only is the octahedrally coordinated Co3+ highly active but also the octahedrally coordinated Co2+ species in CoFe2O4 with an inverse spinel structure shows some activity. These results suggest that the octahedrally coordinated Co2+ species is easily oxidized and shows high catalytic activity for CO oxidation. © 2015 American Chemical Society.

Cavity microelectrodes were used as a binder-free platform to evaluate oxygen evolution reaction (OER) electrocatalysts with respect to gas bubble formation and departure. Electrochemical noise measurements were performed by using RuO2 as a benchmark catalyst and the perovskite La0.58Sr0.4Fe0.8Co0.2O3 as a non-noble metal OER catalyst with lower intrinsic conductivity. Changes in the current during the OER originate from variations in electrolyte resistance during the formation of the gas phase and partial coverage of the active area. Fluctuations observed in current and conductance transients were used to establish the contribution from the ohmic overpotential and to determine the characteristic frequency of oxygen evolution. The proposed quantitative determination of gas bubble growth and departure opens up the route for a rational interface design by considering gas bubble growth and departure as a main contributing factor to the overall electrocatalytic activity at high current densities. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

A good heterogeneous catalyst for a given chemical reaction very often has only one specific type of surface site that is catalytically active. Widespread methodologies such as Sabatier-type activity plots determine optimal adsorption energies to maximize catalytic activity, but these are difficult to use as guidelines to devise new catalysts. We introduce "coordination-activity plots" that predict the geometric structure of optimal active sites. The method is illustrated on the oxygen reduction reaction catalyzed by platinum. Sites with the same number of first-nearest neighbors as (111) terraces but with an increased number of second-nearest neighbors are predicted to have superior catalytic activity. We used this rationale to create highly active sites on platinum (111), without alloying and using three different affordable experimental methods.

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..

The recent surge in investigating electrocatalysts for the H2 evolution reaction is based on finding a cheap alternative to Pt. However platinum's excellent catalytic activity means very little catalyst needs to be used. The present study combines model experiments with numerical modeling to determine exactly how little catalyst is needed. Specifically we investigate ultra-low Pt loadings for use in photoelectrochemical H2 evolution using TiO2-Ti-pn+Si photocathodes. At a current density of 10 mA cm-2, we photocathodically evolve H2 at +465, +450, +350 and +270 mV vs., RHE at Pt loadings of 1000, 200, 50, and 10 ng cm-2 corresponding to HER overpotentials of η1000ng = 32 mV, η200ng = 46 mV, η50ng = 142 mV, and η10ng = 231 mV. To put this in perspective, if 30% of the world's current annual Pt production was used for H2 evolution catalysis, using a loading of 100 ng cm-2 and a current of 10 mA cm-2 would produce 1 TWaverage of H2. The photoelectrochemical data matched the modeling calculations implying that we were near the fundamental maximum in performance for our system. Furthermore modeling indicated that the overpotentials were dominated by mass transfer effects, rather than catalysis unless catalyst loadings were less than 1000 ng cm-2. © The Royal Society of Chemistry.

Different surface sites of solid catalysts are usually quantified by dedicated chemisorption techniques from the adsorption capacity of probe molecules, assuming they specifically react with unique sites. In case of methanol synthesis catalysts, the Cu surface area is one of the crucial parameters in catalyst design and was for over 25 years commonly determined using diluted N2O. To disentangle the influence of the catalyst components, different model catalysts were prepared and characterized using N2O, temperature programmed desorption of H2, and kinetic experiments. The presence of ZnO dramatically influences the N2O measurements. This effect can be explained by the presence of oxygen defect sites that are generated at the Cu-ZnO interface and can be used to easily quantify the intensity of Cu-Zn interaction. N2O in fact probes the Cu surface plus the oxygen vacancies, whereas the exposed Cu surface area can be accurately determined by H2. A combination of N2O reactive frontal chromatography and H2 temperature-programmed desorption is used to analyze the interplay of copper and zinc oxide in methanol synthesis catalysts. This method provides an easy in situ approach to quantify the direct copper-zinc interaction (SMSI effect) and offers an important possibility to rational catalyst design also for other supported metal catalysts. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

Multidimensional shearforce-based constant-distance mode scanning electrochemical microscopy (4D SF/CD-SECM) was utilized for the investigation of the activity distribution of oxygen reduction catalysts. Carbon-supported Pt model catalyst powders have been immobilized in recessed microelectrodes and compared to a spot preparation technique. Microcavities serve as platform for the binder-free catalyst sample preparation exhibiting beneficial properties for constant-distance mode SECM imaging concerning modified surface area and catalyst loading. The integration of the redox competition mode of SECM into the detection scheme of the 4D SF/CD mode is demonstrated for specifically adapting high-resolution SECM experiments to powder-based catalyst preparations. © 2014 Nebel et al.

Nanocrystalline rutile TiO2 powders were modified with small amounts of CuOx and FeOx clusters by impregnation and drying. The modified rutile samples exhibited drastically enhanced photocatalytic degradation of 4-chlorophenol under UV + vis (λ > 320 nm) irradiation. The reaction rates were increased by the factor of 7 and 4 for the optimized TiO2(R)-CuOx and TiO2(R)-FeO x samples containing 0.12 wt.% Cu and 0.13 wt.% Fe, respectively. The visible light (λ > 455 nm) activity in 4-CP degradation was negligible. Photopotential transient measurements have confirmed that amorphous CuOx and FeOx clusters deposited at the surface of rutile TiO2 act as efficient co-catalysts for oxygen reduction by photogenerated electrons, which leads to improved charge separation and diminished recombination. This study shows that simple modification of TiO 2 photocatalysts with redox co-catalysts based on metal oxides is a promising strategy for enhancing the photocatalytic activity in degradation of aqueous pollutants. © 2013 Elsevier B.V.

The development and optimisation of materials that promote electrochemical reactions have recently attracted attention mainly due to the challenge of sustainable provision of renewable energy in the future. The need for better understanding and control of electrode-electrolyte interfaces where these reactions take place, however, implies the continuous need for development of efficient analytical techniques and methodologies capable of providing detailed information about the performance of electrocatalysts, especially in situ, under real operational conditions of electrochemical systems. During the past decade, significant efforts in the fields of electrocatalysis and (electro)analytical chemistry have resulted in the evolution of new powerful methods and approaches providing ever deeper and unique insight into complex and dynamic catalytic systems. The combination of various electrochemical and non-electrochemical methods as well as the application of quantum chemistry calculations has become a viable modern approach in the field. The focus of this critical review is primarily set on discussion of the most recent cutting-edge achievements in the development of analytical techniques and methodologies designed to evaluate three key constituents of the performance of electrocatalysts, namely, activity, selectivity and stability. Possible directions and future challenges in the design and elaboration of analytical methods for electrocatalytic research are outlined. © 2014 The Royal Society of Chemistry.

The efficiency of polymer electrolyte membrane fuel cells is strongly depending on the electrocatalyst performance, that is, its activity and stability. We have designed a catalyst material that combines both, the high activity for the decisive cathodic oxygen reduction reaction associated with nanoscale Pt alloys, and the excellent durability of an advanced nano-structured support. Owing to the high specific activity and large active surface area, the catalyst shows extraordinary mass activity values of 1.0 AmgPt -1. Moreover, the material retains its initial active surface area and intrinsic activity during an extended accelerated aging test within the typical operation range. This excellent performance is achieved by confined space alloying of the nanoparticles in a controlled manner in the pores of the support. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The application of naive Koutecky-Levich analysis to micro- and nano-particle modified rotating disk electrodes of partially covered and non-planar geometry is critically analysed. Assuming strong overlap of the diffusion fields of the particles such that transport to the entire surface is time-independent and one-dimensional, the observed voltammetric response reflects an apparent electrochemical rate constant kapp o, equal to the true rate constant k o describing the redox reaction of interest on the surface of the nanoparticles and the ratio, ψ, of the total electroactive surface area to the geometric area of the rotating disk surface. It is demonstrated that Koutecky-Levich analysis is applicable and yields the expected plots of I -1 versus ω -1 where I is the current and ω is the rotation speed but that the values of the electrochemical rate constants inferred are thereof kapp o, not k o. Thus, for ψ > 1 apparent electrocatalysis might be naively but wrongly inferred whereas for ψ < 1 the deduced electrochemical rate constant will be less than k o. Moreover, the effect of ψ on the observed rotating disk electrode voltammograms is significant, signalling the need for care in the overly simplistic application of Koutecky-Levich analysis to modified rotating electrodes, as is commonly applied for example in the analysis of possible oxygen reduction catalysts. [Figure not available: see fulltext.] © 2014 Tsinghua University Press and Springer-Verlag Berlin Heidelberg.

The effect of Nafion on the performance of a model Cu-modified Pt(111) electrocatalyst has been investigated using electrochemical techniques and density functional theory calculations. In this work, we demonstrate that Cu subsurface alloying not only increases the activity of model Pt(111) electrodes toward the oxygen reduction reaction (ORR) but also largely prevents catalyst poisoning by electrolyte components relevant for polymer electrolyte membrane fuel cell applications. Our results indicate that specific adsorption of (bi)sulfates and sulfonates (present in Nafion membranes) on the Cu-modified Pt(111) electrocatalyst is gradually suppressed, which implies that the ORR activity in 0.05 M H2SO4 electrolyte drastically increases, with a change in the corresponding pseudo-half-wave potential of ∼93 mV. Importantly, the Cu-modified Pt(111) electrocatalyst in contact with Nafion polymer shows an activity as high as that in the absence of this polymer in perchloric acid media. © 2014 American Chemical Society.

The utilization of lignocelluloses (e.g. wood, grass, crops residues and several others) shows great potential as part of the solution for decreasing the dependence of modern societies on fossil resources. In spite of this, the catalytic conversion of these renewable carbon resources via chemical and biotechnological processes is hindered by their complex polymeric nature. For this reason, chemical or enzymatic processes for hydrolysis of cellulose suffer from low efficacy due to harsh reaction conditions and high byproduct formation in case of the chemical methods, or high costs and long reaction times for the enzymatic methods. There is thus an urgent need for processes able to convert the whole plant biomass, which allow the formation of fermentable sugars and technical sulfur-free lignins. Recently, we demonstrated the combination of acid-catalysis with mechanical forces to be an efficient approach to fully overcome the recalcitrance of lignocellulose. As a result, the solvent-free depolymerization of lignocellulose (in solid-state) forms 'water-soluble lignocellulose' in quantitative yield. In this article, we present an overview of the mechanocatalytic depolymerization of lignocellulose and downstream processing of the 'water-soluble' lignocellulose' to sugar alcohols and furfurals. The water-soluble products appear to be the ideal platform at the beginning of advanced value chains of biorefining, starting with 'real' lignocellulosic substrates. © 2014 Elsevier B.V.

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.

The oxygen evolution reaction (OER) is an enabling process for technologies in the area of energy conversion and storage, but its slow kinetics limits its efficiency. We performed an electrochemical evaluation of 14 different perovskites of variable composition and stoichiometry as OER electrocatalysts in alkaline media. We particularly focused on improved methods for a reliable comparison of catalyst activity. From initial electrochemical results we selected the most active samples for further optimization of electrode preparation and testing. An inverted cell configuration facilitated gas bubble detachment and thus minimized blockage of the active surface area. We describe parameters, such as the presence of specific cations, stoichiometry, and conductivity, that are important for obtaining electroactive perovskites for OER. Conductive additives enhanced the current and decreased the apparent overpotential of OER for one of the most active samples (La0.58Sr0.4Fe0.8Co0.2O3). Low-cost electrocatalysts: A family of perovskites has been studied as new electrocatalysts for the oxygen evolution reaction (OER) in alkaline media. Electrochemical characterization demonstrates the promise of this type of materials for the OER, and the use of conductive additives proves useful for obtaining higher current outputs. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The synthesis of yolk-shell catalysts, consisting of platinum or gold-platinum cores and graphitic carbon shells, and their electrocatalytic stabilities are described. Different encapsulation pathways for the metal nanoparticles are explored and optimized. Electrochemical studies of the optimized AuPt, @C catalyst revealed a high stability of the encapsulated metal particles. However, in order to reach full activity, several thousand potential cycles are required. After the electrochemical surface area is fully developed, the catalysts show exceptionally high stability, with almost no degradation over approximately 30 000 potential cycles between 0.4 and 1.4 VRHE. Encapsulation of noble metals in graphitic hollow shells by hard templating is explored as a means for stabilizing fuel cell catalysts. Small platinum particles can be encapsulated, but the achievable loading is too small. Encapsulation of Au-Pt yolk-shell particles allows higher loading, and with such cores, stable catalysts could be produced. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Selective positioning of monolayer amounts of foreign atoms at the surface and subsurface regions of metal electrodes is a promising way to fine-tune the properties of the electrode/ electrolyte interface. The latter is critical as it largely governs the adsorption of electrolyte components and reaction intermediates and, therefore, controls many key electrocatalytic processes. Using model Pt(111) single-crystal electrodes, we demonstrate how the relative position of Cu atoms at the surface drastically changes the adsorption energies for (bi)sulfate anions. Our measurements involve pseudomorphic overlayers of Cu on Pt(111) as well as Cu-Pt(111) surface and sub-surface alloys, where Cu atoms were located either in the first or in the second atomic layers of Pt, respectively. In the case of Cu- Pt(111) surface alloys, specific adsorption of the anions starts earlier compared to the unmodified Pt(111) surface. In contrast, placing Cu atoms into the second atomic layer weakens the binding between the surface and the anions. Surprisingly, Cu pseudomorphic overlayers do not reveal any specific adsorption of (bi)sulfates (within the region of the overlayer stability). Taking into account that electrified interfaces between Pt(111) electrodes and sulfate-containing electrolytes often play the role of benchmark systems in fundamental physico-chemical and, particularly, electrocatalytic studies, our findings demonstrate a promising and relatively easy route of tuning the properties of these interfaces. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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 photocatalytic reduction of CO2 by water vapor to produce light hydrocarbons was studied over a series of catalysts consisting of variable loading of Ti incorporated in TUD-1 mesoporous silica, either modified by ZnO nanoparticles or isolated Cr-sites. Unexpectedly, the performance of ZnO-Ti-TUD-1 and Cr-Ti-TUD-1 was inferior to the parent Ti-TUD-1. An explanation can be found in experiments on the photocatalytic degradation of a mixture of hydrocarbons (i.e., CH4, C2H4, C 2H6, C3H6, and C3H 8) under the same illumination conditions. Ti-TUD-1 exhibits the poorest activity in hydrocarbon degradation, while ZnO-Ti-TUD-1 and Cr-Ti-TUD-1 showed very significant degradation rates. This study clearly demonstrates the importance of evaluating hydrocarbon conversion over photocatalysts active in converting CO2 to hydrocarbons (in batch reactors). © 2013 American Chemical Society.

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.

We describe a solid polyphenylene support that serves as an excellent platform for metal-catalyzed reactions that are normally carried out under homogeneous conditions. The catalyst is synthesized by palladium-catalyzed Suzuki coupling which directly results in formation of palladium nanoparticles confined to a porous polyphenylene network. The composite solid is in turn highly active for further Suzuki coupling reactions, including non-activated substrates that are challenging even for molecular catalysts. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Down to the last detail: Nanostructured solid catalysts were already known in the early 20th century, but their exact structure was unclear. Nowadays, the arrangement of atoms and particles in solids can be manipulated and analyzed down to the atomic scale (see image). The use of specific highly active catalysts enables industrially relevant reactions to be performed at room temperature. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The surface morphology and termination of metal-organic frameworks (MOF) is of critical importance in many applications, but the surface properties of these soft materials are conceptually different from those of other materials like metal or oxide surfaces. Up to now, experimental investigations are scarce and theoretical simulations have focused on the bulk properties. The possible surface structure of the archetypal MOF HKUST-1 is investigated by a first-principles derived force field in combination with DFT calculations of model systems. The computed surface energies correctly predict the [111] surface to be most stable and allow us to obtain an unprecedented atomistic picture of the surface termination. Entropic factors are identified to determine the preferred surface termination and to be the driving force for the MOF growth. On the basis of this, reported strategies like employing "modulators" during the synthesis to tailor the crystal morphology are discussed. © 2014 American Chemical Society.

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.

Split second: The photocatalytic activity of gallium oxide (β-Ga 2O3) depends strongly on the co-catalysts CuOx and chromia, which can be efficiently deposited in a stepwise manner by photoreduction of Cu2+ and CrO42-. The water-splitting activity can be tuned by varying the Cu loading in the range 0.025-1.5 wt %, whereas the Cr loading is not affecting the rate as long as small amounts (such as 0.05 wt %) are present. Chromia is identified as highly efficient co-catalyst in the presence of CuOx: it is essential for the oxidation of water. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A new concept for the localized characterization of gas evolving electrodes based on scanning electrochemical microscopy (SECM) is suggested. It offers information about the spatial distribution of the predominant locations, which represent the most active catalytic sites, and dynamic characteristics of gas-bubble departure. The knowledge about gas-bubble departure is critical for the assessment and development of new electrode materials for energy applications. This journal is © the Partner Organisations 2014.

Recently, the mechanocatalytic depolymerization of lignocelluloses yielding 'water-soluble lignocelluloses' was demonstrated. Water-soluble C5 & C6 sugars and sulfur-free lignins are formed through the saccharification of the oligosaccharides, allowing for the fractionation of biomass by simple filtration. Herein, we present an in-depth analysis of water-soluble products obtained from beechwood. The complex nature of the 'water-soluble beechwood' is investigated by 2D HSQC NMR, HPLC and gel filtration chromatography. The detailed analysis of the 'water-soluble beechwood' lends significant insights into the chemical nature of the lignocellulose depolymerization driven by the mechanical forces. This journal is © the Partner Organisations 2014.

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.

Many photocatalyst systems catalyze chemical reactions under ultraviolet (UV) illumination, because of its high photon energies. Activating inexpensive, widely available materials as photocatalyst using the intense visible part of the solar spectrum is more challenging. Here, nanorod arrays of the wide-band-gap semiconductor zinc oxide have been shown to act as photocatalysts for the aerobic photo-oxidation of organic dye Methyl Orange under illumination with red light, which is normally accessible only to narrow-band semiconductors. The homogeneous, 800-1000-nm-thick ZnO nanorod arrays show substantial light absorption (absorbances >1) throughout the visible spectral range. This absorption is caused by defect levels inside the band gap. Multiple scattering processes by the rods make the nanorods appear black. The dominantly crystalline ZnO nanorod structures grow in the (0001) direction, i.e., with the c-axis perpendicular to the surface of polycrystalline zinc. The room-temperature preparation route relies on controlled cathodic delamination of a weakly bound polymer coating from metallic zinc, an industrially produced and cheaply available substrate. Cathodic delamination is a sequential synthesis process, because it involves the propagation of a delamination front over the base material. Consequently, arbitrarily large sample surfaces can be nanostructured using this approach. © 2014 American Chemical Society.

Determination of the so-called onset potentials, i.e. the lowest (for the anodic reactions) or the highest (for the cathodic reactions) potentials at which a reaction product is formed at a given electrode and at defined conditions, is very important for the evaluation of the catalytic activity and even more for the comparison of different catalysts. We present an approach for the determination of the onset potentials based on scanning electrochemical microscopy (SECM) using the "substrate generation-tip collection" mode. In the proposed method, the potential applied to the catalyst sample is changed stepwise. A micro-electrode serving as SECM tip is positioned in known close proximity to the catalyst surface and is used to detect the onset of the formation of the product of the catalytic reaction, specifically gas generation at the sample surface. The oxygen evolution reaction (OER) at model RuO 2 and perovskite catalyst surfaces is used to evaluate the approach. The suggested method is supposed to provide a clearer and sensitive means for the detection of the onset potentials of electrolytic gas evolution reactions as compared to conventional procedures which mainly use cyclic voltammetry on stationary or rotating (ring) disk electrodes. Moreover, the detection of the reaction product at the SECM tip allows distinguishing between parasitic reactions at the catalyst surface and the true formation of the anticipated reaction product. © 2013 Elsevier B.V. All rights reserved.

Platinum and platinum alloys supported on carbon materials are the state of the art electrocatalysts for the essential oxygen reduction reaction (ORR) in low-temperature fuel cells. The limited stability of such materials under the often detrimental operation conditions of fuel cells still remains a critical issue to improve. In this work, we explore the impact of nitrogen-doped carbon supports on the activity and stability of platinum-based fuel cell catalysts. We present a nitrogen-doped mesostructured carbon material, nitrogen-doped hollow carbon spheres (NHCS), as a support for platinum-based electrocatalysts. A detailed study of the electrochemical activity and stability was carried out for two Pt@NHCS materials i.e., as-made material (Pt@NHCS) with a Pt particle size smaller than 2 nm and the corresponding material after thermal treatment at 850 °C (Pt@NHCST) with a Pt particle size of ca. 2-3 nm. Activity in the ORR was studied by rotating disc electrode (RDE) thin-film measurements, and electrocatalyst stability was evaluated by accelerated aging tests under simulated start-stop conditions. The performance of the NHCS-based materials was compared to the two corresponding nitrogen-free materials as well as to a standard Pt/Vulcan catalyst. The underlying degradation mechanisms of Pt@NHCS materials were investigated via identical location electron microscopy. Our results conclusively show that nitrogen doping of the carbon supports can offer benefits for achieving high initial mass activities due to improved high platinum dispersion; however, it was not found to necessarily lead to an improvement of the catalyst stability. © 2014 American Chemical Society.

A series of highly efficient semiconductor nanocrystal (NC) photocatalysts have been synthesized by growing wurtzite-ZnO tetrahedrons around pre-formed CdS, CdSe, and CdTe quantum dots (QDs). The resulting contact between two small but high-quality crystals creates novel CdX/ZnO heterostructured semiconductor nanocrystals (HSNCs) with extensive type-II nanojunctions that exhibit more efficient photocatalytic decomposition of aqueous organic molecules under UV irradiation. Catalytic testing and characterization indicate that catalytic activity increases as a result of a combination of both the intrinsic chemistry of the chalcogenide anions and the heterojunction structure. Atomic probe tomography (APT) is employed for the first time to probe the spatial characteristics of the nanojunction between cadmium chalcogenide and ZnO crystalline phases, which reveals various degrees of ion exchange between the two crystals to relax large lattice mismatches. In the most extreme case, total encapsulation of CdTe by ZnO as a result of interfacial alloying is observed, with the expected advantage of facilitating hole transport for enhanced exciton separation during catalysis. That's a (quantum dot) wrap! A series of highly active semiconductor photocatalysts have been synthesized by growing wurtzite-ZnO tetrahedrons around pre-formed CdS, CdSe, and CdTe quantum dots. The resulting heterostructured CdX/ZnO nanocrystals with extensive type-II nanojunctions exhibit rapid photocatalytic decomposition of organic molecules in aqueous media. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The search for new and improved methods to synthesize and modify zeolites remains a topic of central academic and industrial relevance. The current reliance on solvent-based methods imposes several drawbacks, including the need for subsequent workup steps and the copious generation of liquid waste. Providing a solvent-and process-efficient, but also a mechanistically-distinct route, mechanochemistry has been postulated as a scalable, one-step approach to overcome these limitations. Uniting essential studies in the field, this perspective explores the potential of mechanochemical methods to contribute to zeolite and zeotype material research. Particular emphasis is given to framework interactions associated with post-synthetic modifications. In addition to the archetypal crystal/particle size reduction, these include the introduction of functionalities by framework activation or ion exchange as well as the moderation of the type, density, and accessibility of active sites by controlled amorphization. The interesting prospects for zeolite catalysis are also discussed. We devise directions to construct a basic understanding of the underlying mechanisms in zeolite-related mechanochemistry, which we expect will broaden its applicability and facilitate the laboratory-to-industry transition. © 2014 Elsevier Ltd. All rights reserved.

Nitrogen-doped carbons derived from biomass precursors were modified with Pt2+ and successfully tested as solid catalysts in the direct oxidation of methane in fuming sulfuric acid. Remarkably, the catalytic performance was found to be substantially better than the Pt-modified Covalent Triazine Framework (CTF) system previously reported, although deactivation is more pronounced for the biomass derived catalyst supports. © 2013 The Royal Society of Chemistry.

The enzyme Trametes hirsuta laccase undergoes direct electron transfer at unmodified nanoporous gold electrodes, displaying a current density of 28μA/cm2. The response indicates that ThLc was immobilised at the surface of the nanopores in a manner which promoted direct electron transfer, in contrast to the absence of a response at unmodified polycrystalline gold electrodes. The bioelectrocatalytic activity of ThLc modified nanoporous gold electrodes was strongly dependent on the presence of halide ions. Fluoride completely inhibited the enzymatic response, whereas in the presence of 150mM Cl-, the current was reduced to 50% of the response in the absence of Cl-. The current increased by 40% when the temperature was increased from 20°C to 37°C. The response is limited by enzymatic and/or enzyme electrode kinetics and is 30% of that observed for ThLc co-immobilised with an osmium redox polymer. © 2012 Elsevier B.V.

The strong influence of the support properties on the activity of gold catalysts has been observed in many publications. The most studied reaction in this respect seems to be CO-oxidation, for which gold catalysts have outstanding activity. However, since in most studies the support properties are also important in influencing the nature of the gold particles deposited on them by co-precipitation or deposition-precipitation, it is difficult to study the support effect alone. We have in a series of studies used colloidal impregnation of preformed gold particles approximately 3nm in size on different supports in order to decouple the gold particle formation from the deposition process, in order to isolate the support effect. Even for such similarly prepared catalysts very strong differences between different supports were observed. The analysis of the data, also in the light of literature data, suggests that there is no unique factor explaining the high activity of gold catalysts, but rather a combination of effects, which act in different proportion for different catalysts. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

One of the technologically most important requirements for the application of supported metal nanoparticles (NPs) to the field of heterogeneous catalysis is the achievement of thermally and chemically stable systems under reaction conditions. For this purpose, a thorough understanding of the different pathways underlying coarsening phenomena is needed. In particular, in depth knowledge must be achieved on the role of the NP synthesis method, geometrical features of the NPs (size and shape), initial NP dispersion on the support (interparticle distance), support pre-treatment (affecting its morphology and chemical state), and reaction environment (gaseous or liquid medium, pressure, temperature). This study provides examples of the stability and sintering behavior of nanoscale systems monitored ex situ, in situ, and under operando conditions via transmission electron microscopy, atomic force microscopy, scanning tunneling microscopy, and X-ray absorption fine-structure spectroscopy. Experimental data corresponding to physical-vapor-deposited and micelle-synthesized metal (Pt, Au) NPs supported on TiO2, SiO2 and Al2O 3 will be used to illustrate Ostwald-ripening and diffusion coalescence processes. In addition, the role of the annealing environment (H2, O2, water vapor) on the stability of NPs will be discussed. © 2013 Springer Science+Business Media New York.

Influential support: Metal substrates affect the chemical properties of ZnO layers, which are important catalyst materials for the industrial production of methanol through the oxidation of CO. Interactions with the substrate lead to the formation of a new, planar ZnO thin-film phase, in which less highly oxidized Zn atoms bind CO more strongly than the Zn atoms in the normal wurtzite modification. 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.

The development of reliable interatomic potentials for large-scale molecular dynamics (MD) simulations of chemical processes at surfaces and interfaces is a formidable challenge because a wide range of atomic environments and very different types of bonding can be present. In recent years interatomic potentials based on artificial neural networks (NNs) have emerged offering an unbiased approach to the construction of potential energy surfaces (PESs) for systems that are difficult to describe by conventional potentials. Here, we review the basic properties of NN potentials and describe their construction for materials like metals and oxides. The accuracy and efficiency are demonstrated using copper and zinc oxide as benchmark systems. First results for a potential of the combined ternary CuZnO system aiming at the description of oxide-supported copper clusters are reported. Model of a copper cluster at the ZnO($10\overline {1} 0$) surface. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nickel pincer complexes of the type [2,6-(R2PO) 2C6H3]NiH (R = tBu, 1a; R = iPr, 1b; R = cPe, 1c) react with BH3·THF to produce borohydride complexes [2,6-(R2PO)2C 6H3]Ni(η2-BH4) (2a-c), as confirmed by NMR and IR spectroscopy, X-ray crystallography, and elemental analysis. The reactions are irreversible at room temperature but reversible at 60 C. Compound 1a exchanges its hydrogen on the nickel with the borane hydrogen of 9-BBN or HBcat, but does not form any observable adduct. The less bulky hydride complexes 1b and 1c, however, yield nickel dihydridoborate complexes reversibly at room temperature when mixed with 9-BBN and HBcat. The dihydridoborate ligand in these complexes adopts an η2- coordination mode, as suggested by IR spectroscopy and X-ray crystallography. Under the catalytic influence of 1a-c, reduction of CO2 leads to the methoxide level when 9-BBN or HBcat is employed as the reducing agent. The best catalyst, 1a, involves bulky substituents on the phosphorus donor atoms. Catalytic reactions involving 1b and 1c are less efficient because of the formation of dihydridoborate complexes as the dormant species as well as partial decomposition of the catalysts by the boranes. © 2012 American Chemical Society.

Driven by mechanical forces, the acid-catalyzed depolymerization of solid biomass completely overcomes the problems posed by the recalcitrance of lignocellulose. The solid-state reaction leads to water-soluble oligosaccharides, which display higher reactivity than cellulose and hemicellulose. Here, we show that water-soluble oligosaccharides are useful feedstock for the high-yield production of 5-hydroxymethylfurfural (HMF) and furfural in biphasic reactors. This is because they readily undergo hydrolysis upon microwave heating, selectively forming monosaccharides as intermediates in the aqueous phase. Short reaction times are possible with the use of microwave heating and limit the extent of degradation reactions. This work provides an ionic-liquid-free approach to process lignocellulosic substrates into HMF and furfural with high yields. In fact, starting this novel approach with α-cellulose, yields of HMF of 79% and furfural of 80% at 443 K for 9 min were obtained. The processing of real lignocellulose (e.g., beechwood and sugar cane bagasse) also achieved high yields of HMF and furfural. Thereby, the current results indicate that the process limitation lies no longer in the recalcitrance of lignocellulose, but in the extraction of highly reactive HMF and furfural from the aqueous phase in the biphasic reactor. © 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.

Nick of time: The nickel cyanomethyl complex 1 catalyzes the room temperature coupling of aldehydes with acetonitrile under base-free conditions. The catalytic system is long-lived and remarkably efficient with high turnover numbers (TONs) and turnover frequencies (TOFs) achieved. The mild reaction conditions allow a wide variety of aldehydes, including base-sensitive ones, to catalytically react with acetonitrile. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

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.

Structural analysis and catalytic testing revealed that zeolite Beta from template-free synthesis introduces new possibilities in catalysis, as a result of its unprecedentedly high density of active sites with exceptional stability and distinctively ordered nature. Highly active and selective catalysts were obtained either by using it in the Al-rich form (e.g. alkylation) or after post-synthesis treatments (e.g. acylation). Such versatility made possible by this novel synthesis route constitutes a new toolbox for catalysis. © 2013 The Royal Society of Chemistry.

Nitrogen-doped carbon materials were synthesized and used as metal-free electrocatalysts for the oxygen reduction reaction (ORR) under alkaline conditions. The synthesis was achieved by thermal treatment of nitrogen-containing polymers diluted in different carbon materials. Polypyrrole, polyaniline and polyacrylonitrile were used as N precursors. Carbon black and two types of commercial carbon nanotubes were used as carbon matrices. The obtained N contents were in the range of 1-1.8 wt.%. Different N species including pyridinic, pyrrolic and quaternary N were quantitatively determined by X-ray photoelectron spectroscopy. The ORR activities were evaluated in 0.1 M KOH. Rotating disc electrode studies revealed the presence of multiple active centers in all the samples. The sample obtained using polypyrrole and small diameter nanotubes (ca. 15 nm) had the highest onset potential at -0.07 V vs. Ag/AgCl/3 M KCl, which also showed a significantly higher electrochemical stability than the sample from carbon black and polypyrrole. The ORR activity was not correlated to the total nitrogen amount, but to the amount of pyridinic and quaternary N species. For the onset potential and the (Npyridinic + Nquaternary)/Ntotal ratio a quasi-linear relation was found, which points to the substantial role of pyridinic- and quaternary-N species in ORR catalysis. © 2013 Elsevier Ltd. All rights reserved.

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.

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.

Incisive modulation of the intermolecular hardness between metalloporphyrins and O2 can lead to the identification of promising catalysts for oxygen reduction. The dependency of the electrocatalytic reduction of O2 by metalloporphyrins on the nature of the central metal yields a volcano-type curve, which is rationalized to be in accordance with the Sabatier principle by using an approximation of the electrophilicity of the complexes. By using electrochemical and UV/Vis data, the influence of a selection of meso-substituents on the change in the energy for the π→π* excitation of manganese porphyrins was evaluated allowing one to quantitatively correlate the influence of the various ligands on the electrocatalysis of O2 reduction by the complexes. A manganese porphyrin was identified that electrocatalyzes the reduction of oxygen at low overpotentials without generating hydrogen peroxide. The activity of the complex became remarkably enhanced upon its pyrolysis at 650 °C. Finding the strength: Incisive modulation of the intermolecular hardness between metalloporphyrins and O2 can lead to the identification of promising catalysts for the oxygen reduction reaction (see figure). The feasibility of this principle is demonstrated in the selection and design of a manganese metalloporphyrin with promising high activity for electrocatalytic oxygen reduction. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Best of both worlds: PtxPdy, Pt, and Pd aerogels with high surface area and porosity can be synthesized in a controlled fashion by a straightforward and environmentally benign strategy. These materials, which are highly active and stable catalysts for the oxygen reduction reaction in PEFC cathodes, combine the high stability of extended surfaces with the high surface area of nanoparticles. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Despite its enormous importance for heterogeneous catalysis, and in particular methanol synthesis, detailed information about the Cu/ZnO interface is still far from being complete. Here we present an overview of recent work carried out using different types of microscopical methods from which the complexity of the problem becomes apparent. In addition to results from transmission electron microscopy (TEM) and scanning electron microscopy (SEM) data also obtained using scanning probe techniques, in particular scanning tunneling microscopy (STM) and atomic force microscopy (AFM) are presented. Special attention is paid to the influence of elevated temperatures on the Cu/ZnO interface. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

Shaken, not stirred: CO oxidation was carried out continuously in a shaker ball mill. During milling, the reaction rate increases dramatically, but drops rapidly to zero when the mill is stopped. Compared to a conventional experiment in a plug-flow reactor, the rate of a ball-mill reaction catalyzed by Cr 2O3 is three orders of magnitude higher at room temperature and one order of magnitude higher at 100°C. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A major practical challenge in heterogeneous catalysis is to minimize the loading of expensive platinum group metals (PGMs) without degrading the overall catalytic efficiency. Gaining a thorough atomic-scale understanding of the chemical/structural changes occurring during catalyst manufacture/operation could potentially enable the design and production of "nano-engineered" catalysts, optimized for cost, stability and performance. In the present study, the oxidation behavior of a Pt-31 at% Pd alloy between 673-1073. K is investigated using atom probe tomography (APT). Over this range of temperatures, three markedly different chemical structures are observed near the surface of the alloy. At 673. K, the surface oxide formed is enriched with Pd, the concentration of which rises further following oxidation at 773. K. During oxidation at 873. K, a thick, stable oxide layer is formed on the surface with a stoichiometry of PdO, beneath which a Pd-depleted (Pt-rich) layer exists. Above 873. K, the surface composition switches to enrichment in Pt, with the Pt content increasing further with increasing oxidation temperature. This treatment suggests a route for tuning the surfaces of Pt-Pd nanoparticles to be either Pd-rich or Pt-rich, simply by adjusting the oxidation temperatures in order to form two different types of core-shell structures. In addition, comparison of the oxidation behavior of Pt-Pd with Pt-Rh and Pd-Rh alloys demonstrates markedly different trends under the same conditions for these three binary alloys. © 2012.

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.

The high prospects of exploiting the oxygen reduction reaction (ORR) for lucrative technologies, for example, in the fuel cells industry, chlor-alkali electrolysis, and metal-air batteries, to name but a few, have prompted enormous research interest in the search for cost-effective and abundant catalysts for the electrocatalytic reduction of oxygen. This chapter describes and discusses the electrocatalysis of oxygen reduction by metallomacrocyclic complexes and the prospect of their potential to be used in fuel cells. Since the main interest of most researchers in this field is to design catalysts which can achieve facile reduction of O2 at a high thermodynamic efficiency, this chapter aims to bring to light the research frontiers uncovering important milestones towards the synthesis and design of promising metallomacrocyclic catalysts which can accomplish the four-electron reduction of O2 at low overpotential and to draw attention to the fundamental requirements for synthesis of improved catalysts. Particular attention has been paid to discussion of the common properties which cut across these complexes and how they may be aptly manipulated for tailored catalyst synthesis. Therefore, besides discussion of the progress attained with regard to synthesis and design of catalysts with high selectivity towards the four-electron reduction of O2, a major part of this chapter highlights quantitative structure-activity relationships (QSAR) which govern the activity and stability of these complexes, which when well understood, refined, and carefully implemented should lead to rational design of better catalysts. A brief discussion about nonmacrocyclic copper (I) complexes, particularly Cu(I) phenanthrolines, and those with a laccase-like structure which exhibit promising activity for ORR has been included in a separate section at the end. © Springer-Verlag London 2013.

The influence of surface Sn-doping on the photocatalytic properties of anatase TiO2 has been investigated in samples prepared by a grafting route using Sn(IV) tert-butoxide as Sn precursor. The grafting procedure leads to the formation of isolated Sn(IV) sites on the surface of anatase TiO2 powders as gauged by structural characterisation based on XRD, Raman spectroscopy and XAS. Studies of the surface reduction based on TPR experiments and XPS provide the conditions for a selective reduction of surface Sn(IV) to the divalent oxidation state. Electronic structure characterisation based on valence band XPS and DRS shows that there is a slight widening of the band gap upon Sn(IV)-grafting, but Sn(II) related states emerge at the top of the main valence band upon reduction at temperatures up to 350°C, and this induces visible light absorption. Grafting of TiO2 with Sn(IV) increases the formation rate of OH radicals on the surface of the material. Reduction of the Sn(IV)-grafted TiO2 to form surface Sn(II) brings about substantial increase of the photocatalytic efficiency for the methylene blue degradation under irradiation with λ≥320nm compared with Sn(IV)-grafted and pure anatase TiO2. This observation is explained based on a surface hole trapping by the Sn(II)-related surface states which lie above the top of the main valence band and can therefore act as trapping sites for holes produced under photoexcitation. © 2013 Elsevier B.V.

The post-synthesis chemical modification of various porous carbon materials with unsaturated organic compounds is reported. By this method, amine, alcohol, carboxylate, and sulfonic acid functional groups can be easily incorporated into the materials. Different carbonaceous materials with surface areas ranging from 240 to 1500 m 2 g -1 and pore sizes between 3.0 and 7.0 nm have been studied. The resulting materials were analyzed by elemental analysis, nitrogen sorption, FTIR spectroscopy, zeta-potential measurements, thermogravimetric analysis, photoelectron spectroscopy, and small-angle X-ray scattering. These analyses indicated that the degree of functionalization is dependent on the nature of the dienophile (reactivity, steric hindrance) and the porosity of the carbon material. As possible applications, the functionalized carbonaceous materials were studied as catalysts in the Knoevenagel reaction and as adsorbents for Pb 2+ from aqueous solution. Making grafting on carbon as easy as grafting on silica? A new and easy approach, based on surface Diels-Alder reactions, allows the introduction of organic functionalities into the framework of mesoporous carbon (see figure). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

A hierarchical carbon-fiber composite was synthesized based on carbon cloth (CC) modified with primary carbon microfibers (CMF) and subsequently secondary carbon nanotubes (CNT), thus forming a three-dimensional hierarchical structure with high BET surface area. The primary CMFs and the secondary CNTs are grown with electrodeposited iron nanoparticles as catalysts from methane and ethylene, respectively. After deposition of Pt nanoparticles by chemical vapor deposition from (trimethyl)cyclopentadienylplatinum, the resulting hierarchical composite was used as catalyst in the electrocatalytic oxygen reduction (oxygen reduction reaction, ORR) as specific test reaction. The modification of the CC with CMFs and CNTs improved the electrochemical properties of the carbon composite as revealed by electrochemical impedance measurements evidencing a low charge transfer resistance for redox mediators at the modified CC. X-ray photoelectron spectroscopy measurements were carried out to identify the chemical state and the surface atomic concentration of the Pt catalysts deposited on the hierarchical carbon composites. The ORR activity of Pt supported on different composites was investigated using rotating disk electrode measurements and scanning electrochemical microscopy. These electrochemical studies revealed that the obtained structured catalyst support is very promising for electrochemical applications, e.g. fuel cells. © 2012 Elsevier Ltd. All rights reserved.

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.

Sol-gel Ru 0.3Sn 0.7O 2 electrode coatings with crack-free and mud-crack surface morphology deposited onto a Ti-substrate are prepared for a comparative investigation of the microstructural effect on the electrochemical activity for Cl 2 production and the Cl 2 bubble evolution behaviour. For comparison, a state-of-the-art mud-crack commercial Ru 0.3Ti 0.7O 2 coating is used. The compact coating is potentially durable over a long term compared to the mud-crack coating due to the reduced penetration of the electrolyte. Ti L-edge X-ray absorption spectroscopy confirms that a TiO x interlayer is formed between the mud-crack Ru 0.3Sn 0.7O 2 coating and the underlying Ti-substrate due to the attack of the electrolyte. Meanwhile, the compact coating shows enhanced activity in comparison to the commercial coating, benefiting from the nanoparticle-nanoporosity architecture. The dependence of the overall electrode polarization behaviour on the local activity and the bubble evolution behaviour for the Ru 0.3Sn 0.7O 2 coatings with different surface microstructure are evaluated by means of scanning electrochemical microscopy and microscopic bubble imaging. © 2012 the Owner Societies.

Benzene can be activated by visible light (λ > 455 nm) in the presence of TiO2, which leads to formation of carbonaceous polymeric deposits on the titania surface. These photosynthesized surface-modified materials exhibit enhanced photoactivity in degradation of phenolic compounds, particularly under visible light irradiation. © 2012 The Royal Society of Chemistry.

Cheers for titania: An N-doped composite of carbon nanotubes (CNTs) and mesoporous TiO 2 is used as support for Pt nanoparticles applied in the oxygen reduction reaction. The composite Pt/N-TiO 2-CNT shows a higher stability than Pt particles on carbon black or N-doped CNTs, as indicated by accelerated stress tests of up to 2000 cycles. The enhanced stability is attributed to strong interactions between TiO 2 and Pt and a higher corrosion resistance of TiO 2 as well as CNTs. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

A new synthesis route for Os-complex modified redox polymers was developed. Instead of ligand exchange reactions for coordinative binding of suitable precursor Os-complexes at the polymer, Os-complexes already exhibiting the final ligand shell containing a suitable functional group were bound to the polymer via an epoxide opening reaction. By separation of the polymer synthesis from the ligand exchange reaction at the Os-complex, the modification of the same polymer backbone with different Os-complexes or the binding of the same Os-complex to a number of different polymer backbones becomes feasible. In addition, the Os-complex can be purified and characterized prior to its binding to the polymer. In order to further understand and optimize suitable enzyme/redox polymer systems concerning their potential application in biosensors or biofuel cells, a series of redox polymers was synthesized and used as immobilization matrix for Trametes hirsuta laccase. The properties of the obtained biofuel cell cathodes were compared with similar biocatalytic interfaces derived from redox polymers obtained via ligand exchange reaction of the parent Os-complex with a ligand integrated into the polymer backbone during the polymer synthesis. © 2011 Elsevier B.V.

The search for more stable electrocatalyst materials for electrochemical energy conversion requires a fundamental understanding of the underlying degradation processes. Advanced characterization techniques like identical location transmission electron microscopy (IL-TEM) can provide invaluable insight into the stability of electrode materials on the nanoscale. In this review, the basic principles and the methodology of IL-TEM are described, and its capabilities are revealed by demonstrating the recent progress that has been achieved in research on the stability of fuel cell catalysts. Moreover, we provide future perspectives of the identical location approach towards implementing other electron microscopic and tomographic applications, which will help us to gain an even broader view of the degradation of electrocatalysts. © 2012 The Royal Society of Chemistry.

A simple method is presented for the formation of thin films of Cu-Pt(111) near-surface alloys (NSA). In these thin films, the solute metal (Cu) is preferentially located in the second platinum layer and protected by a Pt surface layer. The NSA-films act as active and fairly stable electrocatalysts for the reduction of oxygen with the activity and stability which approach those for bulk single crystalline Pt-alloy surfaces and ∼5 times more active than state-of-the-art Pt thin films. © 2012 American Chemical Society.

Metallic copper nanoparticles have been efficiently dispersed and stabilized on nitrogen-doped carbon nanotubes. They are about 8-10 nm in diameter and highly resistant against bulk oxidation. Their catalytic activity and recyclability have been investigated in A 3-type coupling reactions for the synthesis of propargylamines. It was easily possible to prepare diastereomerically pure derivatives of proline and to efficiently recover and reuse the supported catalyst several times. © 2012 Elsevier B.V. All rights reserved.

Characterization of gas evolution reactions at the electrode/electrolyte boundary is often difficult due to the dynamic behavior of interfacial processes. Electrochemical noise measurements determined by scanning electrochemical microscopy were used to characterize Cl 2 evolution at gas-evolving electrodes (GEEs). Analysis of the electrochemical noise is a powerful method to evaluate the efficiency of the catalyst layer at a GEE. The high sensitivity of the developed measurement system enabled accurate monitoring of the current fluctuations caused by gas-bubble detachment from the electrode surface. Fourier transform analysis of the obtained current responses allows extraction of the characteristic frequency, which is the main parameter of the macrokinetics of GEEs. The characteristic frequency was used as part of a methodology to evaluate the catalyst performance and, in particular, to estimate the fraction of the catalyst layer that is active during the gas evolution reaction. Tip of the iceberg: Positioned scanning electrochemical microscopy tips are used to determine the characteristic frequency of gas-bubble detachment from ruthenium-based dimensionally stable anodes at different applied potentials (see picture). Geometrical factors and optimized microstructures of the electrode surface are essential for improving the overall catalytic activity for industrial applications. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

Chemistry at defects: The concentration of defect sites at rutile TiO 2 (r-TiO 2) surfaces of both single crystals and powder particles was determined by UHV-FTIR spectroscopy using CO as a probe molecule (see picture). The potential of this novel approach is demonstrated by unraveling the mechanism of reductive coupling of formaldehyde to give ethylene. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The use of cellulose is hampered by difficulties with breaking up the biopolymer into soluble products. Herein, we show that the impregnation of cellulosic substrates with catalytic amounts of a strong acid (e.g., H 2SO 4, HCl) is a highly effective strategy for minimizing the contact problem commonly experienced in mechanically assisted, solid-state reactions. Milling the acid-impregnated cellulose fully converts the substrate into water-soluble oligosaccharides within 2a H. In aqueous solution, soluble products are easily hydrolyzed at 130°C in 1a H, leading to 91% conversion of the glucan fraction of α-cellulose into glucose, and 96% of the xylans into xylose. Minor products are glucose dimers (8%), 5-hydroxymethylfurfural (1%) and furfural (4%). Milling practical feedstocks (e.g., wood, sugarcane bagasse, and switchgrass) also results to water-soluble products (oligosaccharides and lignin fragments). The integrated approach (solid-state depolymerization in combination with liquid-phase hydrolysis) could well hold the key to a highly efficient "entry process" in biorefinery schemes. Reactive milling: Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Condensation of layered silicate precursors leads to new, all silica zeolite frameworks. In order to introduce catalytic functionality, boron has been substituted into the silicate layer of RUB-39 in a single step synthesis process. Condensation of the silicate layer to the zeolite framework of RUB-41, RRO framework structure type, preserved B as constituent of the material. Analysis of structural details obtained from Rietveld analysis of powder diffraction data, 11B and 29Si NMR experiments of the as synthesized precursor as well as of the zeolite condensation product, and crystal chemical reasoning indicates segregation of B on one specific T-site. This T-site is buried in the silicate anionic layer of the precursor shielding the additional negative charge introduced by the trivalent T-atom. © 2011 Elsevier Inc. All rights reserved.

Nanostructures as catalysts: Pd aerogels modified with α-, β-, and γ-cyclodextrins can be obtained by the spontaneous self-assembly of in situ generated Pd nanoparticles. The Pd aerogels show excellent electrocatalytic activity for the oxidation of ethanol. The catalytic activity is believed to arise from the nonsupported nanometer-scale structure of the aerogel network and the interactions of ethanol with the cyclodextrin. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The activities of four different samples of dimensionally stable anodes (DSA) for the Cl 2 evolution reaction (CER) were analysed and compared with respect to their geometric properties. The samples were made from the same catalyst material, namely mixed oxides of TiO 2 and RuO 2 supported on Ti, following a preparation method in which variations in morphological features of the obtained electrodes were caused by the tensile stress imposed on each sample. The study revealed intriguing correlations between activity, surface area and characteristic morphological features. It is demonstrated that a large number of active sites facilitates high catalytic performance only conditionally, while the overall activity being highly dependent on the accessibility of the active sites to effective transport of the electrolyte, where contribution of surface morphology is crucial for product escape during gas evolution. © 2012 Elsevier Ltd.

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.

After their discovery in the early 1990s, ordered mesoporous materials have become one of the most widely investigated classes of materials, and applications have been considered in many areas, in particular in catalysis. They have attracted attention because of their unique properties such as high surface areas, controllable compositions, crystallinity, thermal and chemical stability, tailored porosities, narrow pore size distributions, concave surface curvatures, surface functionalities, as well as the opportunities they offer for incorporation of catalytically active and selective species. This chapter is focused on the properties of ordered mesoporous solids that distinguish them from more conventional porous catalytic materials. Emphasis is placed on history, development, and methods of synthesis of ordered mesoporous materials. © 2012 Elsevier Inc..

The use of nanostructured yolk-shell materials offers a way to discriminate support and particle-size effects for mechanistic studies in heterogeneous catalysis. Herein, gold yolk-shell materials have been synthesized and used as model catalysts for the investigation of support effects in CO oxidation. Carbon has been selected as catalytically inert support to study the intrinsic activity of the gold nanoparticles, and for comparison, zirconia has been used as oxidic support. Au, @C materials have been synthesized through nanocasting using two different nonporous-core@mesoporous-shell exotemplates: Au@SiO 2@ZrO2 and Au@SiO2@m-SiO2. The catalytic activity of Au, @C with a gold core of about 14nm has been evaluated and compared with Au, @ZrO2 of the same gold core size. The strong positive effect of metal oxide as support material on the activity of gold has been proved. Additionally, size effects were investigated using carbon as support to determine only the contribution of the nanoparticle size on the catalytic activity of gold. Therefore, Au, @C with a gold core of about 7nm was studied showing a less pronounced positive effect on the activity than the metal oxide support effect. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

Recent advances in the synthesis of collidal metal nanoparticles of controlled sizes and shapes that are relevant for catalyst design are reviewed. Three main methods, based on colloid chemistry techniques in solution, i.e., chemical reduction of metal salt precursors, electrochemical synthesis, and controlled decomposition of organometallic compounds and metal-surfactant complexes, are used to synthesize metal nanoparticles. Their catalytic activity and selectivity depend on the shape, size and composition of the metal nanoparticles, and the support effect, as shown for many reactions in quasi-homogeneous and heterogeneous catalysis. A specially designed type of thermally stable catalysts - "embedded" metal catalysts, in which metal nanoparticles are isolated by porous support shells so that metal sintering is effectively avoided at high temperatures, are also introduced. The ultilization of pre-prepared colloidal metal nanoparticles with tuned size, shape and composition as components of designed catalysts opens up new field in catalysis. © 2011 the Owner Societies.

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 interaction of CO with differently modified polycrystalline ZnO has been studied by FTIR spectroscopy under ultrahigh vacuum conditions (UHV-FTIRS). After exposing the clean, adsorbate-free ZnO nanoparticles to CO at 110 K we observe an intense vibrational band at 2187 cm-1 which is assigned to a majority of CO species bound to the Zn2+ sites on the mixed-terminated ZnO(101̄0) surface. After the exposure of CO 2-pretreated ZnO nanoparticles to CO at 110 K, a new CO band is observed at 2215 cm-1, which originates from CO species adsorbed on the "free" Zn sites embedded within the (2 × 1) tridentate carbonate structure on the ZnO(101̄0) surface. UHV-FTIRS data recorded at different sample temperatures demonstrate that the binding energy of CO on polycrystalline ZnO is substantially increased in the presence of pre-adsorbed CO2. The presence of hydroxyl species on the ZnO powder particles does not lead to substantial changes of the CO vibrational bands detected at 110 K under UHV conditions. © 2010 Elsevier B.V. All rights reserved.

High-temperature, stable core-shell catalysts for ammonia decomposition have been synthesized. The highly active catalysts, which were found to be also excellent model systems for fundamental studies, are based on α-Fe 2O 3 nanoparticles coated by porous silica shells. In a bottom-up approach, hematite nanoparticles were firstly obtained from the hydrothermal reaction of ferric chlorides, L-lysine, and water with adjustable average sizes of 35, 47, and 75nm. Secondly, particles of each size could be coated by a porous silica shell by means of the base-catalyzed hydrolysis of tetraethylorthosilicate (TEOS) with cetyltetramethylammonium bromide (CTABr) as porogen. After calcination, TEM, high-resolution scanning electron microscopy (HR-SEM), energy-dispersive X-ray (EDX), XRD, and nitrogen sorption studies confirmed the successful encapsulation of hematite nanoparticles inside porous silica shells with a thickness of 20nm, thereby leading to composites with surface areas of approximately 380 m 2g -1 and iron contents between 10.5 and 12.2wt%. The obtained catalysts were tested in ammonia decomposition. The influence of temperature, iron oxide core size, possible diffusion limitations, and dilution effects of the reagent gas stream with noble gases were studied. The catalysts are highly stable at 750°C with a space velocity of 120000 cm 3 g cat -1h -1 and maintained conversions of around 80% for the testing period time of 33 h. On the basis of the excellent stability under reaction conditions up to 800°C, the system was investigated by in situ XRD, in which body-centered iron was determined, in addition to FeN x, as the crystalline phase under reaction conditions above 650deg;C. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

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.

An active challenge in heterogeneous catalysis is to minimize the quantities of the expensive platinum group metals used without causing degradation of the overall catalytic efficiency in a chemical reaction. To achieve this goal, a thorough atomic-scale understanding of these materials under reactive conditions is required. This will enable the design and production of "nano-engineered" catalysts, optimised for cost, stability and performance. In this study, the oxidation and reduction behaviour of a Pt-Rh alloy between 873 and 1073K was investigated by atom-probe tomography (APT). Detailed observations of the concentration profiles at the oxide/metal interfaces show that the growth of Rh2O3 oxide is limited by diffusion of Rh in the alloy. By varying the oxidation conditions, it was possible to calculate the activation energy for Rh diffusion in Pt-Rh as 236 ± 41 kJ/mol, together with diffusion coefficients for Rh for a range of temperatures. Reduction of the oxide phase left a thin, almost pure, layer of the most reactive (and expensive) element, Rh, on the surface of the specimen, suggesting a simple route for engineering the formation of the core-shell structure Pt-Rh nanoparticles. © 2011 Elsevier B.V. All rights reserved.

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.

Rhodium Drive: Carbon nanotube-supported rhodium sulfide electrocatalysts are prepared by sequential chemical vapor deposition of iron, controlled vapor phase polymerization of thiophene, and finally impregnation of the rhodium precursor and pyrolysis. The electrocatalysts are applied in the oxygen reduction reaction under HCl electrolysis conditions. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A new zeolite catalyst, Al-RUB-41, was synthesized for the first time. It was tested as a catalyst in methanol amination, and showed a shape-selective performance that results in a highly favorable product distribution. The shape-selective nature was also evidenced by using Pt-Al-RUB-41 as a bifunctional catalyst for decane hydroconversion. With its unique pore architecture and remarkable shape-selective character, Al-RUB-41 presents a significant commercial potential in industrial catalysis. © 2011 The Royal Society of Chemistry.

Aluminum was incorporated into the layered silicate RUB-39, which is transformed by calcination into RUB-41. This new zeolite with RRO topology contains 8- and 10-ring pores, and the acid sites in the aluminated material catalyze the synthesis of methylamines, in particular mono- and dimethylamine, by amination of methanol. Owing to the shape-selective catalytic properties of (H)Al-RUB-41, low selectivity to the thermodynamically favored trimethylamine product is obtained in comparison with results on RUB-39 or non-shape-selective materials. Both activity and selectivity are highest for RUB-41 catalysts with a high Si to Al ratio. Silylation reduces the number of unselective sites and results in a further suppression of trimethylamine formation. The introduction of acidity in the intact RUB-41 structure is supported by Al-MAS NMR and NH 3-TPD data. Additional characterization by XRD and SEM is provided. © 2010 Elsevier Inc. All rights reserved.

Photosystem 1 (PS1) catalyzes the light driven translocation of electrons in the process of oxygenic photosynthesis. Isolated PS1 was immobilised on a gold electrode surface via an Os complex containing redox polymer hydrogel which simultaneously is used as immobilisation matrix and as electron donor for PS1. On addition of methyl viologen as sacrificial electron acceptor, a catalytic photocurrent with densities of up to 29 μA cm -2 at a light intensity of 1.8 mW cm -2 was observed upon illumination - equivalent to an incident photon to carrier efficiency (IPCE) of 3.1%. The strong dependence of the catalytic reaction on the light intensity and the dissolved oxygen concentration indicates that a significant photocurrent from excited PS1 to the electrode can only be realized in the presence of oxygen. © 2011 The Royal Society of Chemistry.

A systematic study on the photocatalytic activity of well-defined, macroscopic bulk single-crystal TiO2 anatase and rutile samples has been carried out, which allows us to link photoreactions at surfaces of well-defined oxide semiconductors to an important bulk property with regard to photochemistry, the life time of e-h pairs generated in the bulk of the oxides by photon absorption. The anatase (101) surface shows a substantially higher activity, by an order of magnitude, for CO photo-oxidation to CO2 than the rutile (110) surface. This surprisingly large difference in activity tracks the bulk e-h pair lifetime difference for the two TiO2 modifications as determined by contactless transient photoconductance measurements on the corresponding bulk materials. © 2011 American Physical Society.

Unraveling the complex interaction between catalysts and reactants under operando conditions is a key step toward gaining fundamental insight in catalysis. We report the evolution of the structure and chemical composition of size-selected micellar Pt nanoparticles (∼1 nm) supported on nanocrystalline γ-Al2O3 during the catalytic oxidation of 2-propanol using X-ray absorption fine-structure spectroscopy. Platinum oxides were found to be the active species for the partial oxidation of 2-propanol (< 140 °C), while the complete oxidation (>140 °C) is initially catalyzed by oxygen-covered metallic Pt nanoparticles, which were found to regrow a thin surface oxide layer above 200 °C. The intermediate reaction regime, where the partial and complete oxidation pathways coexist, is characterized by the decomposition of the Pt oxide species due to the production of reducing intermediates and the blocking of O2 adsorption sites on the nanoparticle surface. The high catalytic activity and low onset reaction temperature displayed by our small Pt particles for the oxidation of 2-propanol is attributed to the large amount of edge and corner sites available, which facilitate the formation of reactive surface oxides. Our findings highlight the decisive role of the nanoparticle structure and chemical state in oxidation catalytic reactions. © 2011 American Chemical Society.

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.

A novel continuous method for the preparation of a ternary Cu/ZnO/Al 2O 3 catalyst based on a cascade of micromixers and a tubular aging reactor is presented as a promising alternative route to the conventional batch process. Its application, in combination with immediate spray drying, enables monitoring of the formation of the final precursor by exchange reactions between initially separated phases during the aging step. These exchange reactions were successfully simulated by consecutive precipitation by using micromixers in series as analytical tool. After 60min of continuous aging, calcination, and reduction, a catalyst is produced that exhibits an almost equal mass-related activity in methanol synthesis compared to a commercial catalyst and an area-related activity that is about 50% higher. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nitrogen doping of multi-walled carbon nanotubes (CNTs) was achieved by the carbonization of a polyaniline (PANI) coating. First, the CNTs were partially oxidized with KMnO4 to obtain oxygen-containing functional groups. Depending on the KMnO4 loading, thin layers of birnessite-type MnO2 (10 wt% and 30 wt%) were obtained by subsequent thermal decomposition. CNT-supported MnO2 was then used for the oxidative polymerization of aniline in acidic solution, and the resulting PANI-coated CNTs were finally heated at 550 °C and 850 °C in inert gas. The samples were characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. A thin layer of carbonized PANI was observed on the CNT surface, and the surface nitrogen concentration of samples prepared from 30% MnO 2 was found to amount to 7.6 at% and 3.8 at% after carbonization at 550 °C and 850 °C, respectively. These CNTs with nitrogen-containing shell were further studied by electrochemical impedance spectroscopy and used as catalysts for the oxygen reduction reaction. The sample synthesized from 30 wt% MnO2 followed by carbonization at 850 °C showed the best electrochemical performance indicating efficient nitrogen doping. © 2010 The Royal Society of Chemistry.

An extensive set of characterization methods is required to study the processes occurring during the evolution of the initially amorphous precursor towards the complex Cu/ZnO/Al 2O 3 system. A novel preparation method was therefore developed that provides the possibility of a systematic study of all components in the different stages of the precipitation of the ternary catalyst. As a result, a continuously operating synthesis route was established as an alternative to the industrially applied process. © 2010 Elsevier B.V. All rights reserved.

Nickel hydride with a diphosphinite-based ligand catalyzes the highly efficient reduction of CO2 with catecholborane, and the hydrolysis of the resulting methoxyboryl species produces CH3OH in good yield. The mechanism involves a nickel formate, formaldehyde, and a nickel methoxide as different reduced stages for CO2. The reaction may also be catalyzed by an air-stable nickel formate. © 2010 American Chemical Society.

Exciting new opportunities are emerging in the field of catalysis based on nanotechnology approaches. A new understanding and mastery of catalysis could have broad societal impacts, since about 80% of the processes in the chemical industry depend on catalysts to work efficiently. Efforts in surface science have led to the discovery of new heterogeneous catalysts, however, until recently the only way to develop new or improved catalysts was by empirical testing in trial-and-error experiments. This time-consuming and costly procedure is now rapidly being replaced by rational design methods that utilize fundamental knowledge of catalysts at the nanoscale. The advent of nanoscience and nanotechnology is providing the ability to create controlled structures and geometries to investigate and optimize a broad range of catalytic processes. As a result, researchers are obtaining fundamental insight into key features that influence the activity, selectivity, and lifetime of nanocatalysts. This review article examines several new findings as well as current challenges in the field of nanoparticle based catalysis, including the role played by the particle structure and morphology (size and shape), its chemical composition and oxidation state, and the effect of the cluster support. © 2010 Elsevier B.V. All rights reserved.

(Figure Presented) Cannonball run: Preparation of CO2 has been achieved with CO and O2 coadsorbed onto a Cu(III) surface by illumination with 40 fs pulses of laser light at 400 nm. The hot adatom mechanism that follows O2 dissociation leads to a can-nonball trajectory of the product molecules and thus escape of CO2 from the reactant site to the bare terrace (see figure). It was thus demonstrated that non-adiabatic heterogeneous catalysis may be followed in real space. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

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 Dark Crystal: A hybrid material is reported that is comprised of 1-2 nm sized gold nanoparticles, accessible only through zeolite micropores in a silicalite-1 crystal, as shown by three-dimensional TEM tomography (see picture). Calcination experiments indicate that the embedded nanoparticles are highly stable towards sintering. Figure Equation Present. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.

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.

Cellulose is a renewable and widely available feedstock. It is a biopolymer that is typically found in wood, straw, grass, municipal solid waste, and crop residues. Its use as raw material for biofuel production opens up the possibility of sustainable biorefinery schemes that do not compete with food supply. Tapping into this feedstock for the production of biofuels and chemicals requires-as the first-step-its depolymerization or its hydrolysis into intermediates that are more susceptible to chemical and/or biological transformations. We have shown earlier that solid acids selectively catalyze the depolymerization of cellulose solubilized in 1-butyl-3-methylimidazolium chloride (BMIMCl) at 100°C. Here, we address the factors responsible for the control of this reaction. Both cellulose and solid acid catalysts have distinct and important roles in the process. Describing the depolymerization of cellulose by the equivalent number of scissions occurring in the cellulosic chains allows a direct correlation between the product yields and the extent of the polymer breakdown. The effect of the acid strength on the depolymerization of cellulose is discussed in detail. Practical aspects of the reaction, concerning the homogeneous nature of the catalysis in spite of the use of a solid acid catalyst, are thoroughly addressed. The effect of impurities present in the imidazolium-based ionic liquids on the reaction performance, the suitability of different ionic liquids as solvents, and the recyclability of Amberlyst 15DRY and BMIMCl are also presented. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

A novel electrochemical method to prepare platinum shells around carbon-supported metal nanoparticles (Ru and Au) by pulsed electrodeposition from solutions containing Pt ions is presented. Shell formation is confirmed by characteristic changes in the cyclic voltammograms, and is further evidenced by monitoring particle growth by transmission electron microscopy as well as by energy-dispersive analysis of X rays (EDX). Scanning electrochemical microscopy and EDX measurements indicate a selective Pt deposition on the metal/carbon catalyst, but not on the glassy carbon substrate. The thus prepared carbon-supported core-shell nanoparticles are investigated with regard to their activity in electrocatalytic oxygen reduction, which demonstrates the applicability of these materials in electrocatalysis or sensors. © 2010 Wiley-VCH Verlag GmbH& Co. KGaA, Weinheim.

Tailoring the chemical reactivity of nanomaterials at the atomic level is one of the most important challenges in catalysis research. In order to achieve this elusive goal, fundamental understanding of the geometric and electronic structure of these complex systems at the atomic level must be obtained. This article reports the influence of the nanoparticle shape on the reactivity of Pt nanocatalysts supported on γ-Al2O3. Nanoparticles with analogous average size distributions (∼0.8-1 nm), but with different shapes, synthesized by inverse micelle encapsulation, were found to display distinct reactivities for the oxidation of 2-propanol. A correlation between the number of undercoordinated atoms at the nanoparticle surface and the onset temperature for 2-propanol oxidation was observed, demonstrating that catalytic properties can be controlled through shape-selective synthesis. © 2010 American Chemical Society.

The direct low-temperature oxidation of methane to methanol is demonstrated on a highly active homogeneous molecular catalyst system and on heterogeneous molecular catalysts based on polymeric materials possessing ligand motifs within the material structure. The N-(2-methylpropyl)-4,5-diazacarbazolyl-dichloro-platinum(II) complex reaches significantly higher activity compared to the well-known Periana system and allows first conclusions on electronic and structural requirements for high catalytic activity in this reaction. Interestingly, comparable activities could be achieved utilizing a platinum modified poly(benzimidazole) material, which demonstrates for the first time a solid catalyst with superior activity compared to the Periana system. Although the material shows platinum leaching, improved activity and altered electronic properties, compared to the conventional Periana system, support the proposed conclusions on structure-activity relationships. In comparison, platinum modified triazine-based catalysts show lower catalytic activity, but rather stable platinum coordination even after several catalytic cycles. Based on these systems, further development of improved solid catalysts for the direct low-temperature oxidation of methane to methanol is feasible. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

(Figure Presented) The shape of gold: The title catalyst has been prepared through a colloidal deposition method. Scanning transmission electron microscopy studies confirmed that for the catalyst, gold clusters with a bilayer structure and a diameter of about 0.5 nm are not mandatory to achieve the high activity (see image). © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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 understanding of reaction intermediates in heterogeneous catalysis has important implications for the design of novel catalysts. We investigate the adsorption of CO2 on oxygen precovered Ag(100) at low temperature (17 K) by scanning tunneling microscopy and inelastic electron tunneling manipulation at 5 K. On the terraces, the adsorption leads to O-Ag-CO 2-Ag-O compounds with reduced binding of the oxygen to the surface as compared to the separately adsorbed molecules. The compound can be either dissociated into a bistable O-Ag-CO2 compound at 1.6 V, dissociated into its constituents at 2.2 V, or reacted at 6.5 V into a species, which we tentatively attribute to CO3. The thus obtained carbon trioxide or carbonate is an intriguing reaction intermediate, because it is not stable in the gas phase. Our detailed study of coadsorbed species outlines a possibility to investigate precursors of reactions that involve the substrate atoms. © 2010 American Chemical Society.

A new approach to synthesize nitrogen-doped carbon nanotubes (NCNTs) as catalysts for oxygen reduction by treating oxidized CNTs with ammonia is presented. The surface properties and oxygen reduction activities were characterized by cyclic voltammetry, rotating disk electrode and X-ray photoelectron spectroscopy. NCNTs treated at 800 °C show improved electrocatalytic activity for oxygen reduction as compared with commercially available Pt/C catalysts. © 2009 Elsevier B.V. All rights reserved.

The anisotropic electrocatalytic properties of gold nanobelts and nanoplates enclosed by either {1 1 0} or {1 1 1} facets were studied. Different strategies were used to synthesize these materials. It was found that the {1 1 0} surface of gold does not necessarily show a higher electrocatalytic activity than the {1 1 1} surface. The {1 1 0} surface of gold is more active than the {1 1 1} surface for glucose oxidation in both, neutral and alkaline media. However, for methanol oxidation in alkaline solution, the {1 1 0} surface shows a lower activity than the {1 1 1} surface, which is contrary to the general belief that {1 1 0} facet is the most active surface among the three basal planes. The possible mechanisms are discussed. © 2009 Elsevier B.V. All rights reserved.

New ordered mesoporous carbide derived carbon materials with extraordinary high specific surface areas up to ∼2800 m2 g-1 were synthesized by selective extraction of silicon from ordered mesoporous silicon carbide. Although the degree of mesostructure ordering is lower than that of the CMK-type materials they exhibit higher specific surface areas and high protein adsorption capacities. We show that they can be effectively functionalized with sulfonic groups and become excellent solid acid catalysts for processing large organic molecules. © 2009 American Chemical Society.