ZnO Coatings with Controlled Pore Size, Crystallinity and Electrical Conductivity

Zinc oxide is a wide bandgap semiconductor with unique optical, electrical and catalytic properties. Many of its practical applications rely on the materials pore structure, crystallinity and electrical conductivity. We report a synthesis method for ZnO films with ordered mesopore structure and tuneable crystallinity and electrical conductivity. The synthesis relies on dip-coating of solutions containing micelles of an amphiphilic block copolymer and complexes of Zn2+ ions with aliphatic ligands. A subsequent calcination at 400 °C removes the template and induces crystallization of the pore walls. The pore structure is controlled by the template polymer, whereas the aliphatic ligands control the crystallinity of the pore walls. Complexes with a higher thermal stability result in ZnO films with a higher content of residual carbon, smaller ZnO crystals and therefore lower electrical conductivity. The paper discusses the ability of different types of ligands to assist in the synthesis of mesoporous ZnO and relates the structure and thermal stability of the precursor complexes to the crystallinity and electrical conductivity of the zinc oxide

A meta-analysis of catalytic literature data reveals property-performance correlations for the OCM reaction

Decades of catalysis research have created vast amounts of experimental data. Within these data, new insights into property-performance correlations are hidden. However, the incomplete nature and undefined structure of the data has so far prevented comprehensive knowledge extraction. We propose a meta-analysis method that identifies correlations between a catalyst’s physico-chemical properties and its performance in a particular reaction. The method unites literature data with textbook knowledge and statistical tools. Starting from a researcher’s chemical intuition, a hypothesis is formulated and tested against the data for statistical significance. Iterative hypothesis refinement yields simple, robust and interpretable chemical models. The derived insights can guide new fundamental research and the discovery of improved catalysts. We demonstrate and validate the method for the oxidative coupling of methane (OCM). The final model indicates that only well-performing catalysts provide under reaction conditions two independent functionalities, i.e. a thermodynamically stable carbonate and a thermally stable oxide support

Mesoporous WCx Films with NiO‐Protected Surface: Highly Active Electrocatalysts for the Alkaline Oxygen Evolution Reaction

Metal carbides are promising materials for electrocatalytic reactions such as water electrolysis. However, for application in catalysis for the oxygen evolution reaction (OER), protection against oxidative corrosion, a high surface area with facile electrolyte access, and control over the exposed active surface sites are highly desirable. This study concerns a new method for the synthesis of porous tungsten carbide films with template-controlled porosity that are surface-modified with thin layers of nickel oxide (NiO) to obtain active and stable OER catalysts. The method relies on the synthesis of soft-templated mesoporous tungsten oxide (mp. WOx) films, a pseudomorphic transformation into mesoporous tungsten carbide (mp. WCx), and a subsequent shape-conformal deposition of finely dispersed NiO species by atomic layer deposition (ALD). As theoretically predicted by density functional theory (DFT) calculations, the highly conductive carbide support promotes the conversion of Ni2+ into Ni3+, leading to remarkably improved utilization of OER-active sites in alkaline medium. The obtained Ni mass-specific activity is about 280 times that of mesoporous NiOx (mp. NiOx) films. The NiO-coated WCx catalyst achieves an outstanding mass-specific activity of 1989 A gNi−1 in a rotating-disc electrode (RDE) setup at 25 °C using 0.1 m KOH as the electrolyte.BMBFDFG SPP 2080 priority programPeer Reviewe

A Unified Research Data Infrastructure for Catalysis Research – Challenges and Concepts

Modern research methods produce large amounts of scientifically valuable data. Tools to process and analyze such data have advanced rapidly. Yet, access to large amounts of high-quality data remains limited in many fields, including catalysis research. Implementing the concept of FAIR data (Findable, Accessible, Interoperable, Reusable) in the catalysis community would improve this situation dramatically. The German NFDI initiative (National Research Data Infrastructure) aims to create a unique research data infrastructure covering all scientific disciplines. One of the consortia, NFDI4Cat, proposes a concept that serves all aspects and fields of catalysis research. We present a perspective on the challenging path ahead. Starting out from the current state, research needs are identified. A vision for a integrating all research data along the catalysis value chain, from molecule to chemical process, is developed. Respective core development topics are discussed, including ontologies, metadata, required infrastructure, IP, and the embedding into research community. This Concept paper aims to inspire not only researchers in the catalysis field, but to spark similar efforts also in other disciplines and on an international level. © 2021 The Authors. ChemCatChem published by Wiley-VCH Gmb

A Unified Research Data Infrastructure for Catalysis Research – Challenges and Concepts

Modern research methods produce large amounts of scientifically valuable data. Tools to process and analyze such data have advanced rapidly. Yet, access to large amounts of high‐quality data remains limited in many fields, including catalysis research. Implementing the concept of FAIR data (Findable, Accessible, Interoperable, Reusable) in the catalysis community would improve this situation dramatically. The German NFDI initiative (National Research Data Infrastructure) aims to create a unique research data infrastructure covering all scientific disciplines. One of the consortia, NFDI4Cat, proposes a concept that serves all aspects and fields of catalysis research. We present a perspective on the challenging path ahead. Starting out from the current state, research needs are identified. A vision for a integrating all research data along the catalysis value chain, from molecule to chemical process, is developed. Respective core development topics are discussed, including ontologies, metadata, required infrastructure, IP, and the embedding into research community. This Concept paper aims to inspire not only researchers in the catalysis field, but to spark similar efforts also in other disciplines and on an international level.DFG, 441926934, NFDI4Cat – NFDI für Wissenschaften mit Bezug zur Katalys

Mesoporous WCx Films with NiO‐Protected Surface: Highly Active Electrocatalysts for the Alkaline Oxygen Evolution Reaction

Metal carbides are promising materials for electrocatalytic reactions such as water electrolysis. However, for application in catalysis for the oxygen evolution reaction (OER), protection against oxidative corrosion, a high surface area with facile electrolyte access, and control over the exposed active surface sites are highly desirable. This study concerns a new method for the synthesis of porous tungsten carbide films with template‐controlled porosity that are surface‐modified with thin layers of nickel oxide (NiO) to obtain active and stable OER catalysts. The method relies on the synthesis of soft‐templated mesoporous tungsten oxide (mp. WOx) films, a pseudomorphic transformation into mesoporous tungsten carbide (mp. WCx), and a subsequent shape‐conformal deposition of finely dispersed NiO species by atomic layer deposition (ALD). As theoretically predicted by density functional theory (DFT) calculations, the highly conductive carbide support promotes the conversion of Ni2+ into Ni3+, leading to remarkably improved utilization of OER‐active sites in alkaline medium. The obtained Ni mass‐specific activity is about 280 times that of mesoporous NiOx (mp. NiOx) films. The NiO‐coated WCx catalyst achieves an outstanding mass‐specific activity of 1989 A gNi−1 in a rotating‐disc electrode (RDE) setup at 25 °C using 0.1 m KOH as the electrolyte.BMBF, 03EK3052A, Verbundvorhaben ATO-KAT: Atomar dünn beschichtete poröse Elektroden als neuartige Katalysatoren für die Wasser-Elektrolyse: - leitfähige Träger und Elektrochemie -BMBF, 03EK3052C, Verbundvorhaben ATO-KAT: Quantenchemische Berechnung beschichteter dotierter Metalloxide als Katalysatoren für die OER.DFG,358713534, SPP 2080: Katalysatoren und Reaktoren unter dynamischen Betriebsbedingungen für die Energiespeicherung und -wandlun

Enhanced photocatalytic performance in atomic layer deposition grown TiO2 thin films via hydrogen plasma treatment

The authors report the effect of hydrogen plasma treatment on TiO2 thin films grown by atomic layer deposition as an effective approach for modifying the photoanode materials in order to enhance their photoelectrochemical performance. Hydrogen plasma treated TiO2 thin films showed an improved absorption in the visible spectrum probably due to surface reduction. XPS analysis confirmed the formation of Ti3+ states upon plasma treatment. Hydrogen plasma treatment of TiO2 films enhanced the measured photocurrent densities by a factor of 8 (1 mA/cm(2) at 0.8 V versus normal hydrogen electrode) when compared to untreated TiO2 (0.12 mA/cm(2)). The enhancement in photocurrent is attributed to the formation of localized electronic states in mid band-gap region, which facilitate efficient separation and transportation of photo excited charge carriers in the UV region of electromagnetic spectrum. (C) 2014 American Vacuum Society

Influence of Phase Composition and Pretreatment on the Conversion of Iron Oxides into Iron Carbides in Syngas Atmospheres

CO2 Fischer–Tropsch synthesis (CO2–FTS) is a promising technology enabling conversion of CO2 into valuable chemical feedstocks via hydrogenation. Iron–based CO2–FTS catalysts are known for their high activities and selectivities towards the formation of higher hydrocarbons. Importantly, iron carbides are the presumed active phase strongly associated with the formation of higher hydrocarbons. Yet, many factors such as reaction temperature, atmosphere, and pressure can lead to complex transformations between different oxide and/or carbide phases, which, in turn, alter selectivity. Thus, understanding the mechanism and kinetics of carbide formation remains challenging. We propose model–type iron oxide films of controlled nanostructure and phase composition as model materials to study carbide formation in syngas atmospheres. In the present work, different iron oxide precursor films with controlled phase composition (hematite, ferrihydrite, maghemite, maghemite/magnetite) and ordered mesoporosity are synthesized using the evaporation–induced self–assembly (EISA) approach. The model materials are then exposed to a controlled atmosphere of CO/H2 at 300 °C. Physicochemical analysis of the treated materials indicates that all oxides convert into carbides with a core–shell structure. The structure appears to consist of crystalline carbide cores surrounded by a partially oxidized carbide shell of low crystallinity. Larger crystallites in the original iron oxide result in larger carbide cores. The presented simple route for the synthesis and analysis of soft–templated iron carbide films will enable the elucidation of the dynamics of the oxide to carbide transformation in future work.DFG, 406695057, Fe-basierte Katalysatoren für die Umwandlung von CO2 zu höheren Kohlenwasserstoffen unter dynamischen BedingungenBMBF, 03EK3052A, Verbundvorhaben ATO-KAT: Atomar dünn beschichtete poröse Elektroden als neuartige Katalysatoren für die Wasser-Elektrolyse: - leitfähige Träger und Elektrochemie -DFG, 414044773, Open Access Publizieren 2021 - 2022 / Technische Universität Berli

Oxide-supported carbonates reveal a unique descriptor for catalytic performance in the oxidative coupling of methane (OCM)

The oxidative coupling of methane (OCM) is a promising reaction for direct conversion of methane to higher hydrocarbons. The reaction can be performed over oxide-based catalysts with very diverse elemental composition. Yet, despite decades of research, no general common structure-activity relationship has been deduced. Our recent statistical meta-analysis across a wide range of catalyst compositions reported in the literature suggested that only the catalysts combining thermodynamically stable (under reaction conditions) carbonate and thermally stable oxide support exhibit good catalytic performance. Guided by these findings we explore now experimentally correlations between descriptors for structure, stability and decomposition behavior of supported metal carbonates vs. the materials’ respective performance in OCM catalysis. In this study, carbonates of Rb, Cs and Mg were supported on oxides of Sm, Y, Gd, Ce, Sr and Ba, tested in OCM and studied by IR spectroscopy and thermal analysis. From the evaluation of six proposed property-descriptors we derive a statistically robust volcano-type correlation between the onset temperature of carbonate decomposition and the C2 yield, indicating the importance of CO2 adsorption and surface carbonates in selective methane conversion. Moreover, we discuss mechanisms that can account for the observed property-performance correlation across a wide range of OCM catalysts. Carbonate species are suggested to block highly reactive sites during OCM catalysis, which reduces overoxidation and enables the formation of C2 products

Design of an active and stable catalyst for dry reforming of methane via molecular layer deposition

The dry reforming of methane (DRM) has been proposed as an efficient way to convert two greenhouse gases, namely CO2 and CH4 to syngas. However, most catalysts reported in the literature suffer from strong deactivation during the reforming reaction. The deactivation is caused by strong sintering of catalytically active nanoparticles and the formation of filamentous carbon. Herein a new synthesis procedure based on molecular layer deposition (MLD) is established to stabilize DRM catalysts under reaction conditions. Deactivation of a Ni/SiO2 reference catalyst was prevented by forming a defined porous net-like over-layer, which prevents the sintering and detachment of Ni nanoparticles by filamentous carbon. The MLD approach was further compared to the formation of an overlayer by atomic layer deposition (ALD), demonstrating the advantages of MLD forming hybrid organic-inorganic alucone layers over classical alumina ALD.DFG, 390540038, EXC 2008: Unifying Systems in Catalysis "UniSysCat