Visible-Near-Infrared-Light-Driven Oxygen Evolution Reaction with Noble-Metal-Free WO2-WO3 Hybrid Nanorods

Introducing Oxygen Vacancies into a WO3 Photoanode through NaH2PO2 Treatment for Efficient Water Splitting

WO3, with a high light absorption capacity and a suitable band structure, is considered a promising photoanode material for photoelectrochemical water splitting. However, the poor photoinduced electron-hole separation efficiency limits its application. Herein, we report an effective strategy to suppress electron-hole recombination by introducing oxygen vacancies (OV) on the surface of a WO3 photoanode through NaH2PO2 treatment. An OV-enriched amorphous surface layer with a thickness of 4 nm is formed after NaH2PO2 treatment, which increases the charge carrier density and enlarges the electrochemical surface area of the photoanode. The charge separation and surface injection efficiencies are both improved after NaH2PO2 treatment, and the charge transfer process of the photoanode is accelerated consequently. The current density of the modified WO3 photoanode reaches 0.96 mA cm-2 at 1.23 V.

Micellar Nanoreactors Enabled Site-Selective Decoration of Pt Nanoparticles Functionalized Mesoporous SiO2 /WO3-x Composites for Improved CO Sensing

Site-selective and partial decoration of supported metal nanoparticles (NPs) with transition metal oxides (e.g., FeOx ) can remarkably improve its catalytic performance and maintain the functions of the carrier. However, it is challenging to selectively deposit transition metal oxides on the metal NPs embedded in the mesopores of supporting matrix through conventional deposition method. Herein, a restricted in situ site-selective modification strategy utilizing poly(ethylene oxide)-block-polystyrene (PEO-b-PS) micellar nanoreactors is proposed to overcome such an obstacle. The PEO shell of PEO-b-PS micelles interacts with the hydrolyzed tungsten salts and silica precursors, while the hydrophobic organoplatinum complex and ferrocene are confined in the hydrophobic PS core. The thermal treatment leads to mesoporous SiO2 /WO3-x framework, and meanwhile FeOx nanolayers are in situ partially deposited on the supported Pt NPs due to the strong metal-support interaction between FeOx and Pt. The selective modification of Pt NPs with FeOx makes the Pt NPs present an electron-deficient state, which promotes the mobility of CO and activates the oxidation of CO. Therefore, mesoporous SiO2 /WO3-x -FeOx /Pt based gas sensors show a high sensitivity (31 ± 2 in 50 ppm of CO), excellent selectivity, and fast response time (3.6 s to 25 ppm) to CO gas at low operating temperature (66 °C, 74% relative humidity).

Highly Selective Room Temperature Detection of NH3 and NOx Using Oxygen-Deficient W18O49-Supported WS2 Heterojunctions

In this paper, we reported the controlled synthesis of tungsten disulfide/reduced tungsten oxide (WS₂/W₁₈O₄₉) heterojunctions for highly efficient room temperature NO_x and ammonia (NH₃) sensors. X-ray diffraction analysis revealed the formation of the oxygen-deficient W₁₈O₄₉ phase along with WS₂. Field-emission scanning electron microscopy and transmission electron microscopy displayed the formation of WS₂ flakes over W₁₈O₄₉ nanorods. X-ray photoelectron spectroscopy showed the presence of tungsten in W⁴⁺, W⁵⁺, and W⁶⁺ oxidation states corresponding to WS₂ and W₁₈O₄₉, respectively. The WS₂/W₁₈O₄₉ heterojunction sensor exhibited sub-ppm level sensitivity to NO_x and NH₃ at room temperature. The heterojunction sensor detected 0.6 ppm NO_x and 0.5 ppm NH₃, with a corresponding response of 7.1 and 3.8%, respectively. The limit of detection of the sensor was calculated to be 0.05 and 0.17 ppm for NH₃ and NO_x, respectively. The cyclic stability test showed that the sensor exhibited high stability even after 24 cycles for the detection of NH₃ and 14 cycles for NO_x. Compared to pristine WO₃ and WS₂, the WS₂/W₁₈O₄₉ heterojunction showed high selectivity toward NO_x and NH₃. The results could be useful for the development of room temperature NO_x and NH₃ sensors.

WO3 Nanopores Array Modified by Au Trisoctahedral NPs: Formation, Characterization and SERS Application

The WO₃ nanopores array was obtained by an anodization method in aqueous solution with addition of F^- ions. Several factors affecting the final morphology of the samples were tested such as potential, time, and F^- concentrations. The morphology of the formed nanopores arrays was examined by SEM microscopy. It was found that the optimal time of anodization process is in the range of 0.5-1 h. The nanopores size increased with the increasing potential. The XPS measurements do not show any contamination by F^- on the surface, which is common for WO_x samples formed by an anodization method. Such a layer was successfully modified by anisotropic gold trisoctahedral NPs of various sizes. The Au NPs were obtained by seed-mediated growth method. The shape and size of Au NPs was analysed by TEM microscopy and optical properties by UV-VIS spectroscopy. It was found that the WO₃-Au platform has excellent SERS activity. The R6G molecules could be detected even in the range of 10^-9 M.

Photocatalytic Performance Study of Organophosphorus-Doped Tungsten Trioxide and Composite Materials

The present study successfully produced a highly effective and stable organ phosphorus-doped tungsten trioxide (P-WO3) photocatalyst by a combination of hydrothermal and postcalcination methods. The crystallites, morphologies, and optical properties of the produced WO3 and P-WO3 crystals were investigated. The results indicated that P was consistently doped into the WO3 lattice in a pentavalent-oxidation state (P5+). Additionally, charge carrier traps capable of accepting photoelectrons were created. Additionally, the optical band gap was reduced from 2.4 to 2.33 eV. The degradation of methyl blue by photocatalysts was utilized to evaluate the photocatalytic performance of the synthesized P-WO3 samples at varied P concentrations (MB). The sample containing 6% -P-WO3 exhibited the best photocatalytic performance, degrading 96 percent of MB in 120 minutes, which was more than four times faster than the pure WO3 sample. The practicality of the synthesized P-WO3 was determined using samples from two residential wastewater treatment plants. When treating real wastewater with low organic matter concentrations, the P-WO3 demonstrated strong photodegradation performance. The creation of hydroxyl radicals (OH) and photography-created holes (h+) could be the key protagonists of photocatalytic activity in the P-WO3.

Black Tungsten Oxide Nanofiber as a Robust Support for Metal Catalysts: High Catalyst Loading for Electrochemical Oxygen Reduction

Black valve metal oxides with low oxygen vacancies are identified to be promising for various industrial applications, such as in gas sensing, photocatalysis, and rechargeable batteries, owing to their high reducibility and stability, as well as considerable fractions of low-valent metal species and oxygen vacancies in their lattices. Herein, the nanofiber (NF) of black oxygen-deficient tungsten trioxide (WO_{3- x} ) is presented as a versatile and robust support for the direct growth of a platinum catalyst for oxygen reduction reaction (ORR). The nonstoichiometric, poorly crystallized black WO_{3- x} NFs are prepared by electrospinning the W precursor into NFs followed by their low-temperature (650 °C) reductive calcination. The black WO_{3- x} NFs have adequate electrical conductivity owing to their decreased bandgap and amorphous structure. Remarkably, the oxygen-deficient surface (surface O/W = 2.44) facilitates the growth of small Pt nanoparticles, which resist aggregation, as confirmed by structural characterization and computational analysis. The Pt-loaded black WO_{3- x} NFs outperform the Pt-loaded crystalline white WO_{3- x} NFs in both the electrochemical ORR activity and the accelerated durability test. This study can inspire the use of oxygen-deficient metal oxides as supports for other electrocatalysts, and can further increase the versatility of oxygen-deficient metal oxides.

Self-Hybrid Transition Metal Oxide Nanosheets Synthesized by a Facile Programmable and Scalable Carbonate-Template Method

2D transition metal oxides (TMO) nanosheets have attracted considerable attention in both fundamental research and practical applications. Herein, a convenient programmable and scalable carbonate crystals templating synthesis is developed to produce high-quality self-hybrid TMO nanosheets (Si-WO_{3- x} , Ta_x O_y , Mn_x O_y ) and their respective polymetallic oxide hybrid nanosheets with tunable composition, low-cost and high-yield. Taking tungsten oxide nanosheets as example, silicotungstic acid precursor is in situ converted into tungsten oxide nanosheets like scales on the surface of calcium carbonate crystals through the simple soaking-drying-calcination process, and after selectively dissolving calcium carbonate by etching, the dispersive tungsten oxide nanosheets with unique self-hybrid Si-doped h-WO₃ /ε-WO₃ /WO₂ compositions are obtained, which show excellent acetone gas-sensing performances at low temperatures. This carbonate-template method opens up the possibility to economically produce various functional TMO nanosheets with specific compositions for diverse applications.

Noble Metal-Free FeOOH/Li0.1WO3 Core-Shell Nanorods for Selective Oxidation of Methane to Methanol with Visible-NIR Light

Hydroxyl radicals (^•OH) generated in the photocatalytic process are crucial to the conversion of methane (CH₄) to value-added methanol (CH₃OH) at room temperature. However, utilizing noble metal-free catalysts and low-energy photons of solar light, such as visible and near-infrared light (vis-NIR), is difficult to provide more electron states to form ^•OH radicals. Here, we developed FeOOH/Li_0.1WO₃ core-shell nanorods via a two-step in/out co-modification of hexagonal tungsten oxide (h-WO₃): (1) lithium ions intercalating into the hexagonal tunnels of h-WO₃ to form Li_0.1WO₃ nanorods and (2) using FeOOH-wrapped Li_0.1WO₃ to obtain FeOOH/Li_0.1WO₃ core-shell nanorods. Introduction of lithium induces polaron transition in Li_0.1WO₃, enabling the absorption of vis-NIR light. Interestingly, FeOOH-based Fenton-like reaction when H₂O₂ is selected as an oxidant favors the generation of more ^•OH radicals available for CH₄ oxidation to CH₃OH. Meanwhile, FeOOH with Fe^III as an "electron sink" highly improves the separation of photoinduced electrons and holes in Li_0.1WO₃. Eventually, efficient selective formation of CH₄OH is achieved with remarkable generation rates up to ∼342 and ∼160 μmol g^-1 at visible light (420-700 nm) and NIR light (≥800 nm), respectively. Our finding opens up new possibilities for developing noble metal-free catalysts for solar energy-driven CH₄ conversion to CH₃OH under ambient conditions.

Effect of isothermal holding time on hydrogen-induced structural transitions of WO3

Tungsten trioxide (WO3) has the ability to transform oxygen-deficient structures (WO3-x; 0 ≦ x ≦ 1) at high temperatures under hydrogen. Because the band gap of WO3-x depends on the amount of W5+ species resulting from oxygen vacancies, this material is expected to have unique applications. Herein, to elucidate the WO3 reduction mechanism, we investigated the crystallographic changes of monoclinic WO3 powder samples using X-ray and neutron diffraction measurements under different reduction conditions, namely, under hydrogen at 500 or 800 °C for isothermal holding times of 30 min or 22 h. During heating, the yellow color of WO3 changed to various other colors, suggesting that WO3 underwent different reactions with hydrogen depending on the temperature and isothermal holding time. The X-ray powder diffraction results indicated that the hydrogen-treated WO3 crystals formed various oxygen-deficient structures, including stoichiometric WO3-x, non-stoichiometric WO3-x, and W metal. However, the formation of a single WO3-x phase was extremely difficult. For the blue WO3 sample obtained at short isothermal holding times, the total scattering analysis suggested that the oxygen vacancies in WO3 gradually formed at local positions. Furthermore, the neutron powder diffraction measurements revealed that the reduction of WO3 under hydrogen occurred on the surface. These results obtained by diffraction measurements enhance the knowledge in the chemical and physical properties of WO3-x.

Bifunctional electrocatalysts for oxygen reduction and oxygen evolution: a theoretical study on 2D metallic WO2-supported single atom (Fe, Co, or Ni) catalysts

Catalysts play a critical role in the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) for energy storage, conversion, and utilization. Herein, first-principles density functional theory (DFT) calculations demonstrated that single-metal-atom (Fe, Co, or Ni) sites can bind to the surface of 2D WO2, enhancing the adsorption of intermediates involved in the OER/ORR. Furthermore, it was found that the single-metal-atom-doped 2D WO2 achieves the smallest OER and ORR overpotentials of 0.42 V and 0.40 V, respectively, which are comparable to those of IrO2 or Pt-based catalysts. This predicts the excellent OER/ORR catalytic activities of the single-metal-atom (Fe, Co, or Ni) doped 2D WO2, which would be a promising bifunctional catalyst for fuel cells, water splitting, and metal-air batteries.

Ultrasonically prepared photocatalyst of W/WO3 nanoplates with WS2 nanosheets as 2D material for improving photoelectrochemical water splitting

A sonochemical treatment has been an emerged technique as an interesting method for fabricating different photocatalysts with unique photoelectrochemical (PEC) properties. This study investigated the PEC performance of WO3 with WS2 nanosheets as a 2D material before calcination (WO3/WS2-90) and after calcination (WO3/WS2-450) prepared with sonochemical treatment. The WS2 nanosheets were prepared from a liquid exfoliation phase with few-layer nanosheets, approximately 6.5 nm in thickness. The nanosheets were confirmed by UV-Vis spectroscopy and atomic force microscopy. Further, XPS, RAMAN, and SEM-EDAX analyses indicated that, following calcination of the WO3/WS2 electrode, the WS2 nanosheets initially transformed to 2D-WO3. After depositing the WS2 nanosheets on the WO3, the photocurrent density increased substantially. The WO3/WS2-450 films after calcination showed a photocurrent density of 5.6 mA.cm-2 at 1.23 V vs. Ag/AgCl, which was 3.1 and 7.2 times higher, respectively than those of the WO3/WS2-90 before calcination and pure WO3. Mott-Schottky and electrochemical impedance spectroscopy analyses confirmed the fabrication of the WO3/WS2 photoanode after calcination. The deposition of WS2 nanosheets onto pure WO3 increased the donor concentration (24-fold), reduced the space charge layer (4.6-fold), and decreased the flat band potential (1.6-fold), which could all help improve the photoelectrochemical efficiency. Moreover, the incorporation of WO3 with WS2 nanosheets as a 2D material (WO3/WS2-450) enhanced the incident photon current efficiency (IPCE) by 55%. In addition, the applied-bias photon-to-current conversion efficiency of the WO3/WS2-450 films was approximately 2.26% at 0.75 V (vs. Ag/AgCl), which is 5.6 and 9 times higher, respectively than those of WO3/WS2-90 and pure WO3.

Full-spectrum responsive WO3−x@HA nanotheranostics for NIR-II photoacoustic imaging-guided PTT/PDT/CDT synergistic therapy

A WO_3−x-based nanotheranostic has been successfully fabricated for photoacoustic imaging-guided synergistic tumor targeting therapy in the second near-infrared (NIR-II) biological window.

Photoactive Tungsten-Oxide Nanomaterials for Water-Splitting

This review focuses on tungsten oxide (WO3) and its nanocomposites as photoactive nanomaterials for photoelectrochemical cell (PEC) applications since it possesses exceptional properties such as photostability, high electron mobility (~12 cm2 V-1 s-1) and a long hole-diffusion length (~150 nm). Although WO3 has demonstrated oxygen-evolution capability in PEC, further increase of its PEC efficiency is limited by high recombination rate of photogenerated electron/hole carriers and slow charge transfer at the liquid-solid interface. To further increase the PEC efficiency of the WO3 photocatalyst, designing WO3 nanocomposites via surface-interface engineering and doping would be a great strategy to enhance the PEC performance via improving charge separation. This review starts with the basic principle of water-splitting and physical chemistry properties of WO3, that extends to various strategies to produce binary/ternary nanocomposites for PEC, particulate photocatalysts, Z-schemes and tandem-cell applications. The effect of PEC crystalline structure and nanomorphologies on efficiency are included. For both binary and ternary WO3 nanocomposite systems, the PEC performance under different conditions-including synthesis approaches, various electrolytes, morphologies and applied bias-are summarized. At the end of the review, a conclusion and outlook section concluded the WO3 photocatalyst-based system with an overview of WO3 and their nanocomposites for photocatalytic applications and provided the readers with potential research directions.

Solid-Phase Microwave Reduction of WO3 by GO for Enhanced Synergistic Photo-Fenton Catalytic Degradation of Bisphenol A

The synergistic photocatalytic Fenton reaction is a powerful advanced oxidation technique for the degradation of persistent organic pollutants. However, microwave-induced thermal effects on the formation of novel structures facilitating the photocatalytic degradation have been rarely reported. Herein, a two-step microwave thermal strategy was developed to synthesize a new hybrid catalyst comprising defective WO_3-x nanowires coupled with reduced graphene oxides (rGOs). Conventionally, microwave methods could induce superhot spots on the GO surface, resulting in the site-specific crystallization and oriented growth of WO₃. However, in the solid phase, localized microwave thermal effects could reduce the interfacial area between WO₃ and rGO and enhance the bonding between them. As for the unique structure and surface properties, the synthesized catalyst enhanced the light absorption, promoted the interfacial charge separation, and increased the carrier density in the photocatalytic processes. In addition, surface formation of W⁴⁺ provided a new pathway for Fe³⁺/Fe²⁺ cycling which linked the photocatalytic reaction and the Fenton process. The optimized catalyst exhibited a remarkable performance in the degradation of bisphenol A with a ∼83% removal yield via a photo-Fenton route. These microwave-induced functionalities of materials for synergistic reactions could also give a new avenue to other photoelectrocatalytic fields and solar cells.

Photocatalytic Oxygen Evolution from Water Splitting

Photocatalytic water splitting has attracted a lot of attention in recent years, and O2 evolution is the decisive step owing to the complex four-electrons reaction process. Though many studies have been conducted, it is necessary to systematically summarize and introduce the research on photocatalytic O2 evolution, and thus a systematic review is needed. First, the corresponding principles about O2 evolution and some urgently encountered issues based on the fundamentals of photocatalytic water splitting are introduced. Then, several types of classical water oxidation photocatalysts, including TiO2, BiVO4, WO3, α-Fe2O3, and some newly developed ones, such as Sillén-Aurivillius perovskites, porphyrins, metal-organic frameworks, etc., are highlighted in detail, in terms of their crystal structures, synthetic approaches, and morphologies. Third, diverse strategies for O2 evolution activity improvement via enhancing photoabsorption and charge separation are presented, including the cocatalysts loading, heterojunction construction, doping and vacancy formation, and other strategies. Finally, the key challenges and future prospects with regard to photocatalytic O2 evolution are proposed. The purpose of this review is to provide a timely summary and guideline for the future research works for O2 evolution.

Challenges and implication of full solar spectrum-driven photocatalyst

Conventional metal oxide and its composites embrace the long-standing problem of using the combined visible and near-infrared (NIR) light. Doping with suitable impurities of metal, nonmetal, or its combinations for visible light enhancement is very well studied. However, the quantum efficiency of these photocatalysts does not produce an exciting appearance toward visible and NIR light when irradiated through either artificial or natural light. Furthermore, owing to the limited availability of solar light, challenges arise from the implication of these developed nano-photocatalysts. Therefore, the hybridized concept was developed for the effective use of either full or partial solar spectrum, even functioning in dark conditions. The present review focuses on the challenges of hybridized photocatalysts in storing and discharging the harvested photons obtained from the solar spectrum. The review vividly emphasizes the evolution of light-driven nanomaterials since its innovation and significant breakthroughs in brief, while a detailed presentation of the implications of hybrid photocatalysts for full solar applications, including the mechanistic features, charging-discharging characteristics, work function, charge carrier mobility, and interactions, follows. The article also delivers the substantial contribution of these materials in regard to energy and environmental application.

Growth of W18O49/WOx/W dendritic nanostructures by one-step thermal evaporation and their high-performance photocatalytic activities in methyl orange degradation

A W₁₈O₄₉/WO_x/W dendritic nanostructure was fabricated via self-assembly and acted as an integrated system in the photocatalytic process of MO degradation.

Visible-to-NIR Photon Harvesting: Progressive Engineering of Catalysts for Solar-Powered Environmental Purification and Fuel Production

Utilization of diffusive solar energy through photocatalytic processes for environmental purification and fuel production has long been pursued. However, efficient capture of visible-near-infrared (NIR) photons, especially for those with wavelengths longer than 600 nm, is a demanding quest in photocatalysis owing to their relatively low energy. In recent years, benefiting from the advances in photoactive material design, photocatalytic reaction system optimization, and new emerging mechanisms for long-wavelength photon activation, increasing numbers of studies on the harnessing of visible-NIR light for solar-to-chemical energy conversion have been reported. Here, the aim is to comprehensively summarize the progress in this area. The main strategies of the long-wavelength visible-NIR photon capture and the explicitly engineered material systems, i.e., narrow optical gap, photosensitizers, upconversion, and photothermal materials, are elaborated. In addition, the advances in long-wavelength light-driven photo- and photothermal-catalytic environmental remediation and fuel production are discussed. It is anticipated that this review presents the forefront achievements in visible-NIR photon capture and at the same time promotes the development of novel visible-NIR photon harnessing catalysts toward efficient solar energy utilization.

Carbon dots-decorated Na2W4O13 composite with WO3 for highly efficient photocatalytic antibacterial activity

Photodisinfection by semiconductors has been proven to be an effective method for achieving antibacterial or antifungal activity. However, the toxicity of the nanomaterial to the environment and organisms is a major concern. Herein, a highly efficient and environmentally friendly photodisinfection material of a carbon dots (CDs) decorated Na₂W₄O₁₃ composite with WO₃ photocatalyst was fabricated via a facile hydrothermal-calcination approach. The TEM (transmission electron microscopy) images showed that CDs decorated the surface of the Na₂W₄O₁₃ flakes. Compared with the samples without incorporated CDs, the as-synthesized composite of CDs/Na₂W₄O₁₃/WO₃ exhibited excellent antimicrobial activity against E. coli under visible light illumination. Electron spin resonance (ESR) spectroscopy and reactive species scavenging experiments revealed that the hydroxyl radicals and superoxide radical anions played the most important role in the photocatalytic bacterial inactivation. Furthermore, the cytotoxicity of the CDs/Na₂W₄O₁₃/WO₃ composite was evaluated by analyzing the viability of HepG2 and Chinese hamster lung (V79) cells using Cell Counting Kit-8 (CCK-8).

Phase transformation induced reversible modulation of upconversion luminescence of WO3:Yb3+, Er3+ phosphor for switching devices

The upconverting luminescence properties of phosphors are dependent on the hosts. In this work, the WO₃:Yb³⁺, Er³⁺ phosphor was prepared, and the reversible phase transformation from the WO₃ to the WO₂ was obtained by alternating the sintering in a reducing atmosphere or in air. The influence of reversible phase transformation on the upconversion luminescence was investigated first. The WO₃:Yb³⁺, Er³⁺ phosphor exhibits the visible upconversion luminescence, while no upconversion luminescence was observed in the WO₂:Yb³⁺, Er³⁺ phosphor. The reversible modulation of upconversion luminescence of the WO₃:Yb³⁺, Er³⁺ phosphor retains the excellent reproducibility, exhibiting the potential applications in data storage and optical switches.

Efficient promotion of charge transfer and separation in hydrogenated TiO2/WO3 with rich surface-oxygen-vacancies for photodecomposition of gaseous toluene

Oxygen-deficient TiO₂/WO₃ constructed via the controllable temperature of hydrogen annealing is designed in view of combining the broad visible spectrum absorption with the prominent coupled semiconductor properties. Surface lattice disorder of TiO₂/WO₃ arises at hydrogen annealing temperature of 200 and 300°C, while critical phase transition from TiO₂/WO₃ to TiO₂/WO_2.9 occurs at 400°C, both of which can introduce oxygen vacancies. The hydrogenated TiO₂/WO₃ with rich surface-oxygen-vacancies exhibits much higher photocatalytic activity for decomposition of gaseous toluene than pristine TiO₂/WO₃ under visible-light illumination (λ>420nm). The photoelectrochemical analysis shows that the improved electronic properties of oxygen-deficient TiO₂/WO₃ enable dramatically efficient promotion of photoinduced charge transfer and separation, which is the key factor for the improved photocatalytic activity. It is hoped that the present work could boost ongoing interest for preparing various hydrogenated coupled semiconductors with enhanced activity for diverse photocatalytic applications.

3D Hierarchical heterostructures of Bi2W1−xMoxO6 with enhanced oxygen evolution reaction from water under natural sunlight

Self-assembled 3D hierarchical Bi₂W_1−xMo_xO₆ heterostructures with varying x (x = 0, 0.2, 0.4, 0.6, 0.8 or 1.0) with different morphologies were synthesised via a facile one-pot solvothermal method and their photocatalytic activity towards the oxygen evolution reaction (OER) from water under natural sunlight was tested.

Tungsten-coated nano-boron carbide as a non-noble metal bifunctional electrocatalyst for oxygen evolution and hydrogen evolution reactions in alkaline media

Herein, tungsten-coated nano-boron carbide (W-WB₄-WC_x/B₄C) particles were prepared by heating a mixture of B₄C and W powder using a spark plasma coating (SPC) method. During the discharge treatment process, metal W in the mixture is activated and reacts with B₄C to form WC_x, WB₄, and graphite nanoribbons. The oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performance of W-WB₄-WC_x/B₄C is tested in an alkaline solution, and the results show that the W-WB₄-WC_x/B₄C composite electrocatalyst exhibits a low overpotential of 0.36 V at 10 mA cm^-2 for the OER, a small overpotential of -0.19 V (j = 10 mA cm^-2) for the HER, as well as good stability. The significantly enhanced electrocatalytic performance of the W-WB₄-WC_x/B₄C composites is attributed to their unique structure, in which WC_x and WB₄ not only improve the catalytic activity for the OER and HER, but also effectively anchor the W coating on the substrate.

NH3-assisted chloride flux-coating method for direct fabrication of visible-light-responsive SrNbO2N crystal layers

SrNbO₂N crystal layers were prepared on niobium substrates by using an NH₃-assisted chloride flux-coating method.