Molybdenum - tungsten oxides as prospective photo-anodes for photo-electrochemical water splitting

Enhanced selectivity of platinum-modified tungsten oxide gas sensor through multivariate feature extraction and machine learning algorithms.

Dual-regulation tailoring of tunnel-structured hexagonal tungsten oxide for high-performance ammonium-ion hybrid supercapacitors

Films of nanosized titanium dioxide doped with 0.1–10 mol. % of tungsten ions (hereinafter referred to in the text as W/TiO2) using titanium tetraisopropoxide Ti(OiPr)4 and (NH4)10W12O41·nH2O were obtained by the sol-gel method using non-ionic amphiphilic triblock copolymer Pluronic (P123) as a templating agent. The samples were investigated by XRD, Raman, UV-Vis and FTIR spectroscopy. W/TiO2 dispersions with the same chemical composition have been prepared via gelation of the solution of films precursors, after their drying at room temperature and calcination at 500 °C. Crystalline anatase phase was registered in XRD and Raman spectra of W/TiO2 films up to 10 % tungsten content with a minimum disturbance of the anatase-type structure. XRD patterns of W/TiO2 powders showed anatase (20–25 nm) and rutile (35–40 nm) nanocrystalline phases. The formation of tungsten oxide phases was fixed at its 10 % content. The photocatalytic activity of the films was examined in the photoreduction reaction of Cr(VI) ions to Cr3+ under UV irradiation in the presence of Na2EDTA as an electron donor. Films doped with 5–7 mol. % tungsten ions have higher photocatalytic activity compared to non-doped ones and demonstrated stable activity during 8–10 cycles. The addition of tungsten ions to titania matrix significantly improved its photocatalytic behavior. Tungsten ions doping promotes efficiency of the charge pair separation by trapping of photogenerated electrons with W5+ formation and preventing the charge recombination. When the dopant concentration was increased to 10 %, the photocatalytic efficiency a little decreased. To increase the photocatalytic activity of the coatings, the bare TiO2 and W/TiO2 samples were irradiated in a plasma mixture of hydrogen and argon (1 : 1). The efficiency of undoped TiO2 films has been increased 16 times, and W/TiO2 only by 2 times as the results of tungsten ions affecting the recombination processes.

Ceramic samples of monocomponent (CaO, MgO, ZnO and WO3) and two-component (ZnWO4, MgWO4, CaWO4) compositions were synthesized by direct impact of high-energy electron flow on the charge of stoi chiometric composition. Radiation synthesis of samples weighing about 50 g is realized in time of 10s with out the use of any additional substances to stimulate the process. Systematic studies of the dependence of ra diation synthesis of tungstate ceramics on the flux power density have been performed for the first time. It was found that the dependences of synthesis efficiency on the flux power density of monocomponent (CaO, MgO, ZnO and WO3) and two-component (ZnWO4, MgWO4, CaWO4) ceramic samples have the form of constantly increasing curves. There is a threshold above which the synthesis is realized for all synthesized samples. The effect of mutual influence of charge components on the efficiency of synthesis of two component systems was found. Synthesis of ZnWO4, MgWO4, CaWO4 ceramics is realized under the same conditions of radiation treatment, while the thresholds of synthesis realization of one-component samples of CaO, MgO and ZnO and WO3 ceramics differ significantly. It is shown that at all used modes of radiation treatment the formation of ceramics with the same properties are realized. This effect is due to the inhomoge neous distribution of electron flux energy losses in the substance. Synthesis of two-component (ZnWO4, MgWO4, CaWO4) ceramic samples is realized at the same power density above 1,0 kW/cm2. The radiation synthesis of the ZnWO4, MgWO4, CaWO4 ceramics is mainly determined by tungsten oxide.

Understanding the oxidation of pure tungsten in air and its impact on the lifecycle of a fusion power plant

One-pot synthesis of Fe2O3-supported tungsten trioxide heterojunctions for rapid and highly recyclable photocatalytic nitrobenzene reduction

Abstract Recent advances in photovoltaic (PV) research have highlighted the critical function of the electron transport layer (ETL) in determining solar cell performance, as it governs electron extraction, hole blocking, and interfacial recombination. This work investigates the potential of tungsten trioxide (WO₃) as an ETL in chalcogenide perovskite (CP) solar cells through SCAPS-1D simulation. Two CP absorber materials, BaZrSe₃ and CaHfSe₃, were examined in combination with two benchmark ETLs, titanium dioxide (TiO₂) and tin dioxide (SnO₂), for comparison. The first analysis assessed the influence of ETL type on key PV parameters. Based on the ETL thickness of 100 nm and absorber thickness of 600 nm, SnO₂ consistently yielded the highest power conversion efficiencies (PCEs), while TiO₂ produced the lowest across both absorbers. From the simulated external quantum efficiency (EQE) and current-voltage (J-V) responses, WO₃ demonstrated promising potential despite slightly lower efficiencies than SnO₂. Under identical structural conditions, BaZrSe₃:WO₃ achieved a simulated PCE of 17.70%, whereas CaHfSe₃:WO₃ reached 14.85%, representing 5.9% and 4.8% reductions relative to their respective SnO₂-based configurations. Additional analysis on the effect of ETL thickness confirmed that 100 nm is the optimal value, balancing carrier transport and optical losses. The influence of bulk defect density (Nₜ) showed that device performance degrades significantly when Nₜ ≥ 10¹⁵ cm⁻³, while maintaining Nₜ ≤ 10¹⁴ cm⁻³ ensures higher efficiency. Similarly, interface defect density (Nᵢₙₜ) studies indicated that values below 10¹⁴ cm⁻² are necessary to suppress recombination losses at the absorber/ETL interface. Parasitic resistance analysis showed that higher Rs and lower Rsh mainly limit FF and PCE, underscoring the importance of minimizing resistive losses. To benchmark the present findings, comparisons were made with previous studies, which show that WO₃ delivers acceptable performance relative to other ETL materials, thereby reinforcing the reliability of the current simulation approach. These results underscore the importance of material compatibility and energy-band alignment in optimizing CP solar cell performance. Overall, WO₃ emerges as a viable ETL candidate with strong potential for future development of stable, lead-free, high efficiency CP solar cells.

Electronic behavior and state changes drive tungsten oxide for ultra-low energy consumption dual-band electrochromic smart windows

From hidden danger to rapid detection: silver-enhanced urchin-like tungsten oxide MEMS sensors for Listeria monocytogenes detection in refrigerated dairy.

Coreactant-embedded electrochemiluminescent nanohybrid derived from tungsten oxide quantum dots and its sensing applications for extracellular vesicles in cancer

Over the past few years, two-dimensional transition metal dichalcogenides (TMDCs) have garnered substantial attention in the field of two-dimensional materials research, owing to their exceptional physicochemical properties. Notably, V-WSe2 distinguishes itself by reducing the Schottky barrier at the interface between the material and metal electrodes, thus exhibiting remarkable potential for applications in optoelectronic devices. Our work explores the synthesis of monolayer V-WSe2 through halide-assisted atmospheric-pressure chemical vapor deposition (APCVD), with an emphasis on the effects of various halide types on the growth mechanism. In addition, we investigate the impact of vanadium (V) content on the performance of WSe2. Comprehensive optical and structural characterizations of the synthesized material were systematically performed. The findings indicate that incorporating halide salts effectively reduces the volatilization temperature of tungsten trioxide (WO3), thereby markedly enhancing reaction controllability and material crystallinity. Among the tested halide salts, KCl, NaCl, and KI, KI demonstrated the capability to achieve the lowest growth temperature. Varying the V content in the V-WSe2 structure significantly influences the optical properties, with higher vanadium concentrations reducing the material’s optical bandgap and Raman frequency. This study highlights the critical role of halides and vanadium content in the material growth process, providing valuable insights for the controlled synthesis of two-dimensional TMDC materials and how varying vanadium concentrations also affect the material’s performance.

Tungsten trioxide (WO3) exhibits complementary optical and electrical responses toward hydrogen, yet the interplay between interfacial stress, crystal phase stabilization, and gasochromic/chemiresistive performance remains insufficiently understood. In this work, WO3 films were grown on four single-crystal oxide substrates to systematically tune interfacial stress and thereby modulate the resulting crystal phase, microstructure, and exposed facets. θ–2θ diffraction revealed that WO3 adopts a monoclinic phase on YAlO3 and SrLaAlO4, whereas a high-temperature orthorhombic phase is stabilized on LaAlO3 (LAO) and SrTiO3 due to stronger interfacial constraint. Compared with the amorphous quartz reference, the single-crystal substrates significantly enhanced both gasochromic and chemiresistive responses. In particular, the orthorhombic WO3/LAO film exhibited an electrical response of 1.97 × 104 (Rair/RH2), an optical transmittance changed of 12.7%, and an electrical response time of 1 s toward 2% H2 at 80 °C, far exceeding the monoclinic and amorphous counterparts. The combined effects of stress-induced phase stabilization, film orientation, and hydrogen diffusion pathways are shown to govern the non-monotonic sensing trends among different substrates. These findings elucidate the structural origin of hydrogen sensitivity in WO3 and provide guidance for stress-engineered design of high-performance gasochromic and chemiresistive sensors.

The electrochemistry of transition metal oxides in aqueous electrolytes across the entire pH scale inevitably involves protons. These can interact with oxide electrodes via numerous reactions, including surface adsorption and bulk insertion, electrodissolution/electrodeposition, and water electrolysis. The diversity of electrochemical reactivity involving protons and metal oxide electrodes provides a rich research landscape, while also complicating mechanistic understanding of aqueous batteries. I will discuss proton-insertion coupled electrochemical reactions in tungsten oxides, which are among the few non-noble metal oxides that exhibit good stability in strong acids. Our studies include understanding the mechanism of proton insertion coupled electron transfer from the standpoint of the lattice dynamics, interfacial kinetics, and chemical composition.

In this study, we report the synthesis and optimization of photo-responsive Z-scheme heterostructures composed of tungsten oxide(WO2.9) via hot wire chemical vapor deposition (HWCVD) on the top of cuprous oxide (Cu2O) thin films for efficient, bias-free solar water splitting. The engineered WO2.9/Cu2O heterostructure leverages the synergistic properties of both intrinsic semiconductors to enhance light absorption, charge separation, and photocatalytic performance. Morphological evolution from rod-like to cauliflower-like WO2.9 nanostructures was achieved by tuning tungsten oxide volume. Structural and compositional analysis using X-ray Diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) confirmed high crystallinity and chemical composition. Our findings reveal that Solar-to-Hydrogen (STH) efficiency is highly sensitive to the volume, with volume-dependent synthesis influencing charge carrier dynamics. Electrochemical characterization, including cyclic voltammetry and impedance spectroscopy, demonstrated substantial change in photocurrent density and charge transfer kinetics under simulated solar illumination. The resultant WO2.9/Cu2O photocatalyst, with an optimized W/Cu ratio, shows high and stable photocurrent density(-0.42 A/m2). The optimized heterostructures achieved maximum current density and STH efficiency are 0.42 and 1% respectively, which demonstrates excellent photochemical stability and highlights its strong potential for scalable and sustainable green hydrogen production. Keywords: Photocatalysis, Hydrogen evolution, Z-scheme, Heterojunction, Tungsten oxide

Tungsten trioxide (WO3) is a well-known, non-toxic n-type semiconductor with remarkable properties, such as a low band gap (2.4-2.8 eV), moderate hole diffusion length, and a favorable valence band (VB) position for water oxidation. These attributes make WO3 suitable for applications in photocatalysis and photoelectrochemical water splitting (PEC), among other fields. PEC is particularly important due to its ability to generate gaseous H2, a green fuel of the future, using non-carbon energy sources. However, the development of efficient WO3-based photoelectrodes requires addressing challenges like a low absorption coefficient of WO3 and significant electron hole recombination. WO3 can be synthesized using number of methods, including CVD, hydrothermal and solvothermal synthesis, sol-gel processing, electrodeposition, and anodic oxidation (anodization). Electrochemical methods, particularly anodization, offer a highly controlled approach to produce WO3 layers with diverse morphologies directly on current collectors, thereby significantly reducing system resistance. The properties of anodic WO3 can be tailored through the appropriate selection of electrolyte composition, applied voltage, and process temperature. Many previous studies have reported efficient anodization in electrolytes containing fluoride ions, which however, pose environmental hazards. [1-2]Therefore, our work focuses on a green anodization approach using environmentally friendly electrolytes. For the first time, we present a comprehensive optimization of W anodization in selected organic acid-based electrolytes, addressing critical aspects relevant to PEC applications. In this study, we investigate the effects of electrolyte composition, applied voltage, and anodization temperature on the morphological characteristics and chemical/phase composition of the resulting anodic materials. Moreover, we examine how these anodization parameters influence the photoelectrochemical activity of the obtained photoanodes.The electrodes were characterized using various techniques: SEM, EDS, XRD, UV-Vis DRS, and Raman spectroscopy. Analyses of the annealed electrodes confirmed of the formation of highly crystalline, nanoporous WO3. The photoelectrochemical performance of the synthesized photoanodes was tested in a three-electrode system in 0.1 M Na2SO4 using 1.5 AM G simulated solar light. Additionally, monochromatic light tests in the 300-500 nm range were conducted to assess changes in the incident photon to current efficiency (IPCE), as expected from differences in light absorption. The results indicate that our photoanodes have a morphology that is preferred from the point of view of photoelectrochemical applications and consequently show good activity in PEC.This research is part of the project No. 2022/47/P/ST5/00813 co-funded by the National Science Center and the European Union Framework Program for Research and Innovation Horizon 2020 under the Marie Sklodowska-Curie grant agreement no. 945339.[1] Hao, Z. et al., Sustain. Energy Fuels 2021, 5, 2893–2906. https://doi.org/10.1039/D1SE00109D[2] Zych, M. et al., Molecules 2020, 25, 2916. https://doi.org/10.3390/molecules25122916

Fuel cell stacks for heavy-duty vehicle (HDV) applications must achieve over 50,000 hours of durability.1, 2 The durability of proton exchange membranes (PEMs) is a critical factor in reaching this goal. At present, cerium (Ce) ions are employed to improve the PEM's durability. However, it has been reported that Ce migration both in-plane and through-plane within the membrane,3 triggered by fuel cell operation, causes performance degradation.4 Although augmenting the Ce ion concentration is one strategy to fulfill the durability requirements of HDV applications, this approach tends to exacerbate performance trade-offs, further complicating issues related to efficiency and thermal management. Consequently, it is vital to develop methods for extending durability without increasing the Ce content. In this study, we explored the possibility of using tungsten oxide (WOx), renowned for its hydrogen peroxide decomposition capability and stability in highly acidic conditions,5 in conjunction with Ce ions, known for their superior OH radical decomposition,6 to boost durability while minimizing performance trade-offs. This presentation outlines the durability in open-circuit voltage (OCV) hold tests and I-V performance conducted with membrane electrode assemblies (MEAs) prepared from cast Nafion membranes with Ce ions and WOx (where x=2 or 3). The findings indicate that integrating WOx with Ce ions, leveraging their distinct functionalities, can achieve a cumulative durability improvement arising from each additive's individual effect with no significant impact on the I-V performance. Fuel Cell Technology Development Roadmap for FCVs and HDVs, New Energy and Industrial Technology Development Organization (NEDO), (2024) https://www.nedo.go.jp/content/100973008.pdf. D. A. Cullen, K. C. Neyerlin, R. K. Ahluwalia, R. Mukundan, K. L. More, R. L. Borup, A. Z. Weber, D. J. Myers and A. Kusoglu, Nature Energy, 6, 462 (2021). B. Kienitz, B. Pivovar, T. Zawodzinski and F. H. Garzon, Journal of The Electrochemical Society, 158, B1175 (2011). Y.-H. Lai, K. M. Rahmoeller, J. H. Hurst, R. S. Kukreja, M. Atwan, A. J. Maslyn and C. S. Gittleman, Journal of The Electrochemical Society, 165, F3217 (2018). P. Trogadas and V. Ramani, Journal of The Electrochemical Society, 155, B696 (2008). M. Danilczuk, S. Schlick and F. D. Coms, Macromolecules, 42, 8943 (2009).

Our recent research interests concentrate on the development, characterization, as well as establishing relation between structure and reactivity of functionalized materials for efficient electrocatalysis and electrochemical energy conversion. There has been growing attention in the electrochemical reduction of carbon dioxide, a potent greenhouse gas and a contributor to global climate change. Given the fact that the CO2 molecule is very stable, its electroreduction processes are characterized by large overpotentials. To optimize the hydrogenation-type electrocatalytic approach, we have proposed to utilize nanostructured metallic centers (e.g. palladium) in a form of highly dispersed and reactive nanoparticles generated within supramolecular network of distinct nitrogen, sulfur or oxygen-coordination complexes. Among important issues are the mutual completion between hydrogen evolution and carbon dioxide reduction and specific interactions between coordinating centers and metallic sites. We have also explored the ability of biofilms to form hydro-gel-type aggregates of microorganisms attached to various surfaces including those of carbon electrode materials. Upon incorporation of various noble metal nanostructures and/or conducting polymer ultra-thin films, highly reactive and selective systems toward CO2-reduction have been obtained. Another possibility to enhance electroreduction of carbon dioxide is to explore direct transformation of solar energy to chemical energy using transition metal oxide semiconductor materials. We show here that, by intentional and controlled combination of metal oxide semiconductors (Cu-intercalated tungsten(VI) oxide and copper (I) oxide), we have been able to drive effectively photoelectrochemical reduction of carbon dioxide mostly to methanol.Application of metal oxides as active matrices in electrocatalysis is particular importance. The hydrous behavior, which favors proton mobility and affects overall reactivity, reflects not only the oxide’s chemical properties but its texture and morphology as well. For example, the mixed oxide (WO3 and ZrO2) systems are characterized by fast charge (electron, proton) propagation during the system’s redox transitions. By dispersing metallic Cu electrocatalytic nanoparticles over such active WO3-based supports, the electrocatalytic activities of the respective systems toward the reduction of carbon dioxide have been enhanced even at decreased loadings in acid media. The fact that the oxide nanostructures are in immediate contact with the metallic catalytic sites leads to the specific interactions (via the surface hydroxyl groups) with the reaction intermediates (e.g. CO adsorbates).Formation of ammonia is one of the most important chemical synthetic processes. Under industrial conditions, ammonia is primarily been synthesized from nitrogen and hydrogen via the Haber-Bosch process which requires pressurizing and heating, despite utilization of catalysts. Consequently, development of low-temperature synthetic methodology is tempting both from the practical and fundamental reasons. An ultimate goal for electrochemistry is to generate NH3 from N2 at temperatures lower than 100ºC, atmospheric pressure, and with use of new generation of catalysts. Currently, most of electrochemical approaches to drive N2-fixation suffer from slow kinetics due to the difficulty of achieving the appropriate adsorption and activation of dinitrogen molecule leading to cleavage of the strong triple N≡N bond. Our recent studies, clearly demonstrate that coordinatively stabilized iron catalytic sites, e.g. iron-centered heme-type porphyrins or iron phosphides, have been found to act as efficient catalysts for the formation of NH3 in alkaline and semi-neutral media.

Magnetron sputtering is a well known technique that allows in particular the deposition of semi-conducting transition metal oxide (TMO) thin films using a metallic target and a Ar/O2 plasma. Amorphous carbon nitride (a-CNx) thin layers can also be deposited using this same technique with the help of a graphite target and a Ar/N2 plasma. This technique offers various highly influencing deposition parameters among which one can cite total pressure, oxygen partial pressure, power, and substrate heating temperature. A post-treatment of the obtained thin films, such as annealing under a controlled atmosphere, is often suitable so as to master and/or improve their cristallinity. Some of these TMOs and a-CNx thin films can be very interesting candidates as photoanode or photocathode materials as such but they can also be combined together so as to develop semiconductor junctions, targeting in our work a photoelectrochemical water splitting application.In this contribution, a brief overview of recent investigations dealing with i) WO3 thin films, ii) their junctions with CuOx (CuO, Cu2O, Cu3O4) thin films all produced by magnetron sputtering, or TiO2 nanotube arrays produced by anodization, and iii) semi-conducting a-CNx thin films will be presented. The chemical and structural characterizations of these semi-conducting thin films and of their junctions were performed using nuclear techniques (Nuclear Reaction Analysis (NRA), Rutherford Backscattering Spectrometry (RBS), Elastic Recoil Detection Analysis (ERDA), collaboration with the SAFIR platform, INSP, Sorbonne Université, Paris, France), XRD and Raman spectroscopy, whereas UV-visible spectrophotometry and Tauc plots were exploited in order to define their opto-electronic properties. Conducting AFM was also used to map the surface electronic conductivity of these TMO and a-CNx layers at the nanometric scale so as to correlate it with the topography and the composition of the thin layers. All the data thus collected were then used to explain and optimise the photo-electrochemical performance, determined with the help of photocurrent measurements under chopped ligth, of tungsten trioxide thin films and their junctions with other semiconducting transition metal oxides. In this purpose, their photo-electrochemical behaviour was explored using Mott-Schottky plots and Electrochemical Impedance Spectroscopy under illumination.

Ammonium-ion batteries are increasingly attracting attention for their inherent advantages. The small ion hydration radius and light molar mass enable faster ion transport. Neutral or weakly acidic electrolytes are eco-friendly and safe. H-bonding between NH4 + carriers and host materials offers better rate performance than metal ion coordination bonds during insertion. However, achieving high-rate performance and long-term stability remains challenging due to sluggish ion transport and structural instability in electrode materials.In this presentation, an amorphous tungsten oxide coated carbon cloth (a-WO3@CC) with well-connected multi-dimensional diffusion channels, enabling high-performance ammonium-ion storage will be shown. Compared with conventional bulk WO3, which primarily relies on rigid one-dimensional (1D) ion tunnels, a-WO3 features a nanocrystalline-stacked amorphous framework, forming interconnected ion diffusion networks that facilitate NH₄⁺ insertion and transport. The disordered atomic arrangement and abundant short-range ordered domains further enhance ion diffusion kinetics, while the optimized amorphous structure accommodates structural stress, ensuring excellent cycling stability. Besides, Plentiful oxygen vacancies and surface-adsorbed oxygen-containing groups lead to a higher capacity. As a result, its exceptional ammonium-ion storage capacity is as high as 2783 mA cm⁻2, more than double that of conventional bulk polycrystalline WO3. It also exhibits outstanding rate capability and cycle stability. When it is paired with a polyaniline-coated carbon cloth (PANI@CC) cathode in a full AIB, the assembled device delivers an extraordinary energy density of 630 mWh cm⁻2. This study provides new insights into the rational design of amorphous nanostructured materials with well-connected ion diffusion pathways for next-generation high-rate energy storage systems.