Reactivity of hydrogen and methanol on (001) surfaces of WO3, ReO3, WO3/ReO3 and ReO3/WO3

Mechanistic Insights into WO3 Sensing and Related Perspectives

Tungsten trioxide (WO₃) is taking on an increasing level of importance as an active material for chemoresistive sensors. However, many different issues have to be considered when trying to understand the sensing properties of WO₃ in order to rationally design sensing devices. In this review, several key points are critically summarized. After a quick review of the sensing results, showing the most timely trends, the complex system of crystallographic WO₃ phase transitions is considered, with reference to the phases possibly involved in gas sensing. Appropriate attention is given to related investigations of first principles, since they have been shown to be a solid support for understanding the physical properties of crucially important systems. Then, the surface properties of WO₃ are considered from both an experimental and first principles point of view, with reference to the paramount importance of oxygen vacancies. Finally, the few investigations of the sensing mechanisms of WO₃ are discussed, showing a promising convergence between the proposed hypotheses and several experimental and theoretical studies presented in the previous sections.

Unraveling the Structure and Properties of Layered and Mixed ReO3-WO3 Thin Films Deposited by Reactive DC Magnetron Sputtering

Tungsten trioxide (WO₃) is a well-known electrochromic material with a wide band gap, while rhenium trioxide (ReO₃) is a "covalent metal" with an electrical conductivity comparable to that of pure metals. Since both WO₃ and ReO₃ oxides have perovskite-type structures, the formation of their solid solutions (ReO₃-WO₃ or Re _x W_1-x O₃) can be expected, which may be of significant academic and industrial interest. In this study, layered WO₃/ReO₃, ReO₃/WO₃, and mixed ReO₃-WO₃ thin films were produced by reactive DC magnetron sputtering and subsequent annealing in air at 450 °C. The structure and properties of the films were characterized by X-ray diffraction, optical spectroscopy, Hall conductivity measurements, conductive atomic force microscopy, scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoemission spectroscopy. First-principles density functional theory calculations were performed for selected compositions of Re _x W_1-x O₃ solid solutions to model their crystallographic structure and electronic properties. The calculations predict metallic conductivity and tetragonal distortion of solid solutions in agreement with the experimental results. In contrast to previously reported methods, our approach allows us to produce the WO₃-ReO₃ alloy with a high Re content (>50%) at moderate temperatures and without the use of high pressures.

Hydride species on oxide catalysts

Hydride species on oxide catalysts are widely involved in oxide-catalyzed reactions, and relevant fundamental understanding is important to establish reaction mechanisms and structure-performance relations of oxide catalysts. In this topical review, recent progresses on the formation and reactivity of hydride species on the surface or in the bulk of oxides are briefly summarized. Firstly, characterization techniques for hydride species are introduced. Secondly, formation of hydride species on the surface or in the bulk of various oxides and their reactivity in oxide-catalyzed hydrogenation and dehydrogenation reactions are reviewed. Finally, short summary and outlook are given.

Discovery of Acid-Stable Oxygen Evolution Catalysts: High-Throughput Computational Screening of Equimolar Bimetallic Oxides

Discovering acid-stable, cost-effective, and active catalysts for oxygen evolution reaction (OER) is critical since this reaction is a bottleneck in many electrochemical energy conversion systems. The current systems use extremely expensive iridium oxide catalysts. Identifying Ir-free or less-Ir containing catalysts has been suggested as the goal, but no systematic strategy to discover such catalysts has been reported. In this work, we perform first-principles-based high-throughput catalyst screening to discover OER-active and acid-stable catalysts focusing on equimolar bimetallic oxides with space groups derived from those of IrO_x. We develop an approach to evaluate acid-stability under the reaction condition by utilizing the Materials Project database and density functional theory (DFT) calculations. For acid-stable materials, we further investigate their OER catalytic activities and identify promising OER catalysts that satisfy all the desired properties: Co-Ir, Fe-Ir, and Mo-Ir bimetallic oxides. Based on the calculated results, we provide insights to efficiently perform future high-throughput screening to discover catalysts with desirable properties and discuss the remaining challenges.

Comparative Ab Initio Calculations of ReO3, SrZrO3, BaZrO3, PbZrO3 and CaZrO3 (001) Surfaces

We performed, for first time, ab initio calculations for the ReO2-terminated ReO3 (001) surface and analyzed systematic trends in the ReO3, SrZrO3, BaZrO3, PbZrO3 and CaZrO3 (001) surfaces using first-principles calculations. According to the ab initio calculation results, all ReO3, SrZrO3, BaZrO3, PbZrO3 and CaZrO3 (001) surface upper-layer atoms relax inwards towards the crystal bulk, all second-layer atoms relax upwards and all third-layer atoms, again, relax inwards. The ReO2-terminated ReO3 and ZrO2-terminated SrZrO3, BaZrO3, PbZrO3 and CaZrO3 (001) surface band gaps at the Γ–Γ point are always reduced in comparison to their bulk band gap values. The Zr–O chemical bond populations in the SrZrO3, BaZrO3, PbZrO3 and CaZrO3 perovskite bulk are always smaller than those near the ZrO2-terminated (001) surfaces. In contrast, the Re–O chemical bond population in the ReO3 bulk (0.212e) is larger than that near the ReO2-terminated ReO3 (001) surface (0.170e). Nevertheless, the Re–O chemical bond population between the Re atom located on the ReO2-terminated ReO3 (001) surface upper layer and the O atom located on the ReO2-terminated ReO3 (001) surface second layer (0.262e) is the largest.

First-principles study of the surface reactions of aminosilane precursors over WO3(001) during atomic layer deposition of SiO2

Energy diagram of reaction pathways for decomposition of different aminosilane precursors on a WO₃ (001) surface.

Atomic layer deposition of diisopropylaminosilane on WO3(001) and W(110): a density functional theory study

The decomposition reaction mechanisms of the Si precursor, diisopropylaminosilane (DIPAS), on W(110) and WO₃(001) surfaces are compared using the density functional theory (DFT) method.

Tuning of the crystal engineering and photoelectrochemical properties of crystalline tungsten oxide for optoelectronic device applications

WO₃crystals with {002} or {111} facets primarily exposed, WO₃films with dominant orientations, doping and heterostructuring are highlighted.

Fabrication of (001)-oriented monoclinic WO3 films on FTO substrates

(001)-oriented monoclinic nanorod and microplate WO3 films are fabricated on commercial FTO-coated glass substrates by a rubbing seed layer and a spin-coating seed layer assisted by hydrothermal reactions. The nanorod film obtained by the rubbing seed layer assisted by hydrothermal reactions is more regular and perpendicular to the substrate.