Tungsten Oxide Layer Research Articles

Electrochemical Production of Tungsten Oxides from Wc-Co Carbide-Type Pseudo-Alloy Waste

Electrochemical research is devoted to the development of a method of processing secondary raw materials containing tungsten in the form of a pseudoalloy of the carbide type WC–Co in sulfate solutions. The target processing products are: powders of tungsten oxides of lower oxidation states, which can be reduced to metallic tungsten with lower costs. Using the methods of linear and cyclic voltammetry, it was established that the selective dissolution of the cobalt component of the pseudoalloy in the studied solutions occurs at potentials more positive than 0.2 V, carbon is removed from the working electrode at a potential > 0.8 V. At the same time, tungsten is oxidized to the higher oxide WO3. It was determined that in sulfuric acid, with an increase in its concentration from 1 to 5 mol∙dm-3, the current density decreases, which is associated with the formation of a solid surface layer of tungsten oxide on the surface of the anode, which passivates the surface. It was established experimentally that when adding 1 mol∙dm-3 of H2SO4 hexamine (C6H12N4) with a concentration of 0.9 mol∙dm-3 to a solution, it is possible to block the process of formation of a passivating film and obtain powders of tungsten oxides of lower oxidation states.

Coordination and Hydrogen Bond Chemistry in Tungsten Oxide@Polyaniline Composite toward High-Capacity Aqueous Ammonium Storage.

Aqueous ammonium ion batteries (AAIBs) have garnered significant attention due to their unique energy storage mechanism. However, their progress is hindered by the relatively low capacities of NH4 + host materials. Herein, the study proposes an electrodeposited tungsten oxide@polyaniline (WOx@PANI) composite electrode as a NH4 + host, which achieves an ultrahigh capacity of 280.3 mAh g-1 at 1 A g-1, surpassing the vast majority of previously reported NH4 + host materials. The synergistic interaction of coordination chemistry and hydrogen bond chemistry between the WOx and PANI enhances the charge storage capacity. Experimental results indicate that the strong interfacial coordination bonding (N: →W6+) effectively modulates the chemical environment of W atoms, enhances the protonation level of PANI, and thus consequently the conductivity and stability of the composites. Spectroscopy analysis further reveals a unique NH4 +/H+ co-insertion mechanism, in which the interfacial hydrogen bond network (N-H···O) accelerates proton involvement in the energy storage process and activates the Grotthuss hopping conduction of H+ between the hydrated tungsten oxide layers. This work opens a new avenue to achieving high-capacity NH4 + storage through interfacial chemistry interactions, overcoming the capacity limitations of NH4 + host materials for aqueous energy storage.

ВЛИЯНИЕ ПЕРИОДИЧЕСКОЙ МОДУЛЯЦИИ УГЛА НАНЕСЕНИЯ ВОЛЬФРАМОКСИДНЫХ СЛОЕВ ПРИ МАГНЕТРОННОМ НАПЫЛЕНИИ НА ИХ ЭЛЕКТРИЧЕСКИЕ ХАРАКТЕРИСТИКИ

Submicron tungsten oxide (WO3) layers of 50-250 nm thickness were obtained by magnetron deposition. The resulting films structure was adjusted in the course of magnetron sputtering using a method based on the modulation of electrochromic tungsten oxide (VI) deposition angle developed in our earlier studies. The prepared WO3 layers were used for the manu-facture of electrochromic devices which electrical characteristics were studied by cyclic volt-amper¬ometry using a three-electrode connection scheme. Based on the obtained data, coefficients of Li+ ions diffusion were calculated and found to follow an ex¬treme dependence upon the speed of tungsten oxide deposition angle modulation with a maximum at speed about 1.2 rpm.

Enhancing durability of automotive fuel cells via selective electrical conductivity induced by tungsten oxide layer coated directly on membrane electrode assembly.

The poor durability, attributed to catalyst corrosion during start-up/shutdown (SU/SD), is a major obstacle to the commercialization of fuel cell electric vehicles (FCEVs). We recently achieved durability enhancement under SU/SD conditions by implementing a metal-insulator transition (MIT) using proton intercalation/deintercalation in WO3. However, such oxide-supported catalysts were unsuitable for direct application to the mass production stage of membrane electrode assembly (MEA) process due to their physical and chemical properties. Here, we report a unique approach that achieves the same durability enhancement in SU/SD situations while being directly applicable to the conventional MEA fabrication process. We coated WO3 on the bipolar plate, gas diffusion layer, and MEA to investigate whether the MIT phenomenon was realized. The WO3-coated MEA demonstrated 94% performance retention during SU/SD, the highest level to our knowledge. It can directly contribute to enhancing the durability of commercial FCEVs and be immediately applied to the MEA mass production process.

Defective Engineering Tuning the Analog Switching Linearity and Symmetry of Two‐Terminal Artificial Synapse for Neuromorphic Systems

AbstractNeuromorphic computing inspired by memristors has gained considerable attention due to its low power and easy integration. However, state‐of‐the‐art two‐terminal resistive switching memristors based on conductive filament formation suffer from high variability and poor controllability. As a three‐terminal device operated through electrochemistry and dynamic insertion/extraction of ions, the electrochemical ion synapse demonstrates deterministic control of electron conductivity based on ion doping. But, integrating the electrochemical ion synapse into crossbar arrays will pose higher challenges and lower integration density. Herein, inspired by first‐principles calculations, a two‐terminal bidirectional plasticity electrochemical artificial synapse with integrated lithium polymer electrolyte and polycrystalline tungsten oxide layer is reported. The linearity and stability of the device weight update are greatly improved by adjusting the defect concentration of the polycrystalline WO3 layer. Even after 16 000 write‐read events in the air, its performance remained almost unchanged. Moreover, it has an over‐limit protection mechanism under one‐way stimulation that exceeds the normal range. Based on this excellent stability, the authors designed and successfully simulated the “muscle memory” that the programmatical organization of the nervous system leads to proficiency in specific actions.

In situ formed nickel tungsten oxide amorphous layer on metal–organic framework derived ZnxNi1−xWO4 surface by self-reconstruction for acid hydrogen evolution reaction

Noble metal free electrocatalysts for hydrogen evolution reaction (HER) in acid play an important role in proton exchange membrane-based electrolysis. Here, we develop an in situ surface self-reconstruction strategy to construct excellent acidic HER catalysts. Firstly, free-standing zinc nickel tungstate nanosheets inlaid with nickel tungsten alloy nanoparticles were synthesized on carbon cloth as pre-catalyst via metal–organic framework derived method. Amorphous nickel tungsten oxide (Ni-W-O) layer is in situ formed on surface of nanosheet as actual HER active site with the dissolution of NiW alloy nanoparticles and the leaching of cations. While the morphology of the free-standing structure remains the same, keeping the maximized exposure of active sites and serving as the electron transportation framework. As a result, benefiting from disordered arrangement of atoms and the synergistic effect between Ni and W atoms, the amorphous Ni-W-O layer exhibits an excellent acidic HER activity with only an overpotential of 46 mV to drive a current density of 10 mA cm−2 and a quite good Tafel slope of 36.4 mV dec−1 as well as an excellent durability. This work enlightens the exploration of surface evolution of catalysts during HER in acidic solution and employs it as a strategy for designing acidic HER catalysts.

Deposition of Nanostructured Tungsten Oxide Layers by a New Method: Periodic Modulation of the Deposition Angle.

Periodic modulation of the deposition angle (PMDA) is a new method to deposit nanostructured and continuous layers with controllable periodic density fluctuation. The method is used for the magnetron sputtering of a WO3 layer for an electrochromic device (ECD). An experimental study indicates that the electrochromic coloration-bleaching rate nearly doubles and the electrochromic efficiency grows by about 25% in comparison with the traditional method. The ECD efficiency rises with the increasing degree of nanostructure ordering, surface roughness, and homogeneity of the WO3 layer. The method is promising for coating deposition techniques needed to produce versatile devices with specific requirements for ion transport in surface layers, coatings, and interfaces, such as fuel cells, batteries, and supercapacitors.

WO3 layer sensitized with BiVO4 and MIL-101(Fe) as photoanode for photoelectrochemical water oxidation

Thick tungsten oxide layers were prepared electrophoretically in order to be used as photoanodes in photoelectrochemical water oxidation applications. The highest photocurrent density was obtained for a WO3 layer with thickness of ∼900 nm. Additionally, WO3/BiVO4 and WO3/BiVO4/MIL-101(Fe) heterojunctions have been fabricated using WO3 layer as substrate. WO3/BiVO4 shows an increased value of the electrochemical active surface area indicating that more sites of this photoanode are activated through the formation of the heterojunction. The small V5+ signals observed in the V 2p XPS spectra of these heterojunctions were attributed to the substitution of V5+ atoms with W6+ atoms on the surface of BiVO4. Excessive W doping of the BiVO4 film determined the decrease of the photoelectrochemical performance of WO3/BiVO4 photoanode. The significant improvement of the photoconversion efficiency of the sample decorated with MIL-101(Fe) indicated that this co-catalyst provides sites more efficiently in the photoelectrochemical process. This performance was correlated with the reduced value of the charge transfer resistance at electrode/electrolyte interface obtained from electrochemical impedance spectroscopy investigation.

Oxygen stabilized W−Ag films for environmental antibacterial applications

Oxygen was added into sputter deposited tungsten films to reduce residual stress of the films, and silver with content up to 14.3 at.% was further added for antibacterial functionalization. The films were analyzed by SEM-EDX, XPS and XRD. Only X-ray diffraction peaks from β-W or W3O phase were detected for the films. Oxygen and silver existed mainly as solid solution atoms in the films. Silver addition decreased hardness (still ≥10.3 GPa) and elastic modulus of the films. The potentiodynamic polarization demonstrated lower corrosion current density of the WO film than that of the tungsten film, and silver changed corrosion behavior of the films. The Ag-depleted tungsten oxide layer on the film surface suppressed the release of silver ions in water. The WOAg films had good antibacterial activity with E.coli bacteria. The WOAg films would be useful in environmental and other antimicrobial applications.

Impact of Ionic Liquid Additives and Inorganic Fullerene-Like Tungsten Disulfide on Friction and Wear under Aqueous Environments.

Aqueous lubricants are gaining attention due to significant advantages such as being environmentally friendly, tunable, and thermally stable. The oil and gas industry can use such additives to utilize in water-based fluids for applications where small sliding velocities and large lateral forces require enhanced lubrication. This investigation aims to compare the effects of two different additives: (i) inorganic fullerene-like tungsten disulfide (IF-WS2) and (ii) an alkanolamine ionic liquid denoted as AA-IL. Both additives were paired with three different base fluids, deionized water (DIW), aqueous NaCl, and aqueous CaCl2, to measure the impact on fluids commonly utilized in the field. The addition of IF-WS2 to all three solutions resulted in a 30-60% decrease in the coefficient of friction (COF) and wear. Surface analysis by X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS) showed that the formation of a tribofilm (tungsten oxide layer) is primarily responsible for tribological improvements. The AA-IL did not show evidence of any chemical interaction. Instead, a physically bonded film of the AA-IL on the steel surface enabled the improved COF (40-50% reduction) and wear response. Both additives are effective in very small amounts and provide excellent wear and friction reduction properties.

Tuning the visible light activity of tungsten oxide layers by changing the anodization conditions

Photoelectrochemical water splitting under solar radiation is one of the most studied methods of solar-to-fuel energy conversion. The search for effective photoelectrode materials operating under solar radiation is still ongoing, and in this paper, it is shown how to control the optical and photoelectrochemical properties of anodic tungsten oxide layers by changing the anodizing potential. Anodic tungsten oxide layers were obtained in an aqueous electrolyte with 1 M ammonium sulfate and 75 mM ammonium fluoride at a constant voltage of 20–70 V and annealed at 500 °C in air. Comprehensive characterization of materials was performed using SEM, XRD, UV–Vis DRS, Mott-Schottky analyses, and photoelectrochemical water splitting tests. It was found that with increasing the anodizing potential the band gap narrows from 3.09 eV to 2.75 eV, donor density increases, and the IPCE spectrum shifts towards the visible light range.

Recessed-Channel WSe2 Field-Effect Transistor via Self-Terminated Doping and Layer-by-Layer Etching.

Effective channel control with low contact resistance can be accomplished through selective ion implantation in Si and III-V semiconductor technologies; however, this approach cannot be adopted for ultrathin van der Waals materials. Herein, we demonstrate a self-aligned fabrication process based on self-terminated p-doping and layer-by-layer chemical etching to achieve low contact resistance as well as a high on/off current ratio in ultrathin tungsten diselenide (WSe2) field-effect transistors (FETs). Damage-free layer-by-layer thinning of the WSe2 channel is repeated up to a thickness of approximately 1.4 nm, while maintaining the selectively p-doped source/drain regions. The device characteristics of the recessed-channel WSe2 FET are systematically monitored during this layer-by-layer recess-channel process. The WSe2 etching rate is estimated to be 2-3 layers per cycle of oxidation and subsequent chemical etching. The self-terminated tungsten oxide (WOX) layer grown through ultraviolet-ozone treatment induces robust p-doping in the neighboring (or underlying) WSe2 through the electron withdrawal mechanism, which remains in the source/drain regions after channel oxide removal. The adopted self-terminated and self-aligned recess-channel process for ultrathin WSe2 FETs enables the realization of a high on/off output current ratio (>108) and field-effect mobility (∼190 cm2/V·s), while maintaining low contact resistance (0.9-6.1 kΩ·μm) without a postannealing process. The proposed facile and reproducible doping and atomic-layer-etching method for the fabrication of a recessed-channel FET with an ultrathin body can be helpful for high-performance two-dimensional semiconductor devices and is applicable to post-Si complementary metal-oxide semiconductor devices.

High-Efficiency WSe2 Photovoltaic Devices with Electron-Selective Contacts.

A rapid surge in global energy consumption has led to a greater demand for renewable energy to overcome energy resource limitations and environmental problems. Recently, a number of van der Waals materials have been highlighted as efficient absorbers for very thin and highly efficient photovoltaic (PV) devices. Despite the predicted potential, achieving power conversion efficiencies (PCEs) above 5% in PV devices based on van der Waals materials has been challenging. Here, we demonstrate a vertical WSe2 PV device with a high PCE of 5.44% under one-sun AM1.5G illumination. We reveal the multifunctional nature of a tungsten oxide layer, which promotes a stronger internal electric field by overcoming limitations imposed by the Fermi-level pinning at WSe2 interfaces and acts as an electron-selective contact in combination with monolayer graphene. Together with the developed bottom contact scheme, this simple yet effective contact engineering method improves the PCE by more than five times.

Enriched In2O3/WO3 nanocomposites as photoanode for a dye-sensitized solar cell in photo powered energy system

Tungsten oxide nanoparticles (PWNPs) and indium/tungsten oxide nanocomposites (IWNCs) were synthesized by the facile hydrothermal method. Powder X-ray diffraction (XRD) results confirmed the formation of the orthorhombic and body-centered cubic crystalline structure of PWNPs and IWNCs. An increase in roughness of IWNCs than PWNPs was evident through atomic force microscopy (AFM), which in turn increases the electrical conductivity of IWNCs. Dye-sensitized solar cells (DSSCs) for PWNPs and IWNCs were investigated as electron-transport layers in planar DSSCs. The integration of indium in the tungsten oxide layer led to enhanced power conversion efficiency (PCE) of about 4.69% due to the electron transfer and reduced back-recombination.

Understanding on the hydrogen detection of plasma sprayed tin oxide/tungsten oxide (SnO2/WO3) sensor

The plasma spray technique was well proven in producing metal oxide based gas sensors in the last two decades using different powder feedstocks. However, limited research was made to fabricate hydrogen gas sensor from tin oxide layer coated over tungsten oxide layer. This paper attempts to interpret the hydrogen gas sensing performances of plasma sprayed coating derived by depositing tin oxide layer over tungsten oxide (SnO2/WO3) layer. Plasma sprayed SnO2/WO3 sensor showed maximum response of 90% at 150 °C in contrast to stand-alone WO3 (89% at 350 °C) and stand-alone SnO2 (89% at 250 °C). The lower operating temperature of SnO2/WO3 sensor without compromising gas response was attributed to the WO3–SnO2 hetero-junction. SnO2/WO3 sensor showed selective sensing towards hydrogen with respect to carbon monoxide and methane gases. This sensor also possessed repeatable characteristics after 39 days from the initial measurement. In a nut-shell, plasma spayed SnO2/WO3 sensor showed stability of base resistance, repeatability after successive response and recovery cycles, selective sensing towards 500 ppm H2 with significant magnitude of gas response of 90%, response time of 35 s and recovery time of 269 s at a temperature of 150 °C.

ITO-free silver-doped DMD structures: HiPIMS transparent-conductive nano-composite coatings for electrochromic applications

Nanocomposites of dielectric/metal/dielectric (DMD) materials that are both optically transparent and electrically conductive are of great interest for an array of modern optoelectronic applications, including electrochromic and energy storage devices. Here we report for the first time the creation of ITO-free DMD nanocomposite structures that are composed of only three layers: (Ag-doped WO3)/(Ag)/(WO3). We employed high power impulse magnetron sputtering (HiPIMS) as a new technology to deposit the internal WO3 layer and the external Ag/WO3 nanocomposite. High rates of silver ionization in the HiPIMS process and energetic arrival of silver ions on the negatively biased DMD structure enabled their penetration into the external tungsten oxide layer, forming a nanocomposite structure in a single-step process. We provided evidence that this unique structure pushes the performance of transparent-conductive DMD materials beyond their intrinsic limits. To optimize the surface plasmon resonance effect and thus the electrochromic performance of the structures, we changed the size of silver nanoclusters through vacuum post-annealing in the same sputtering chamber at varied temperatures. The optimized Ag-WO3/Ag/WO3 structure was transparent (average transmittance = 75.89 ± 0.05% in the wavelength range of 300–700 nm) and electrically conductive (sheet resistance = 23.6 ± 0.8 Ω/□). Moreover, it showed favorable electrochromic characteristics with high coloration efficiency (32.1 cm2 C−1), fast switching speed, and excellent long-term stability for at least 2000 cycles. The mechanisms of improvement in the electrochromic performance of such bifunctional structures underpinned by surface plasmon resonance, as modulated by the size and average distance of silver nanoclusters, are elucidated. The versatile new approach using HiPIMS for the fabrication of transparent-conductive nanocomposite coatings on ITO-free substrates holds great potential to manufacture next-generation optoelectronic materials such as electrochromic devices.

First post-mortem analysis of deposits collected on ITER-like components in WEST after the C3 and C4 campaigns

In order to map the complex plasma footprint observed on the lower divertor of the WEST experiment after its first phase of operation, we analysed deposits collected on ITER-like Plasma Facing Units (PFUs) exposed in the C3 (deuterium plasma) and C4 (deuterium and helium plasma) campaigns. Our results show that these deposits have multilayer structures mainly composed of tungsten, oxygen, boron and carbon, whose texture and composition vary along the radial direction. These traits allowed us to identify three types of deposits: deposits rich in boron (conditioning) in the low plasma flux area further away from the strike point, deposits rich in tungsten with traces of metallic compounds (Cu, Fe, Cr, Ni, Ag) in the high plasma flux area and deposits rich in boron and tungsten in the private flux area. In addition, we found more nanoparticles, voids and tungsten oxide layers in the deposits formed during C4 in comparison to that of C3.

Comprehensive Electrical modeling analysis of Heterojunction Perovskite Solar Cells by using different electron transport nanostructured layers

Abstract A Comprehensive Electrical modeling analysis of Heterojunction Perovskite Solar Cells by using different nanostructures Electron transport layers is accomplished. COMSOL Multiphysics commercial package was used to design and analyze an optoelectronic model of different device structures of the electron transport layers of Perovskite Solar Cell; mainly single layer, bi-layer, and sandwich structures. This was achieved by investigating three metal oxide materials namely: ZnO, TiO2, and WO3. The results show an enhancement in the device performance by using the sandwich structure of TiO2/ZnO/TiO2 at thicknesses of (10/50/20) nm with a power conversion efficiency of 19.26%. While the study revealed that the least efficient electron transport layer is a single tungsten oxide layer at a thickness ~10 nm) with a power conversion efficiency of 12.14%.

Visible-light sensitization of anodic tungsten oxide layers with CuWO4

Anodic tungsten oxide is an attractive material for photoelectrochemical water splitting under solar irradiation, however due to several limitations, it absorbs only UV light and, therefore, one of the challenges is to transfer its photoresponse to the visible light region. In this paper, for the first time, it is proposed sensitization of anodic WO3 layers with copper tungstate by a wet impregnation method. The CuWO4–WO3 materials are obtained by immersion of anodic layers in a copper acetate solution and annealing at 500 °C in air atmosphere. As-received materials are characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD), and Raman spectroscopy, Mott–Schottky measurements and photoelectrochemical (PEC) tests. Proposed visible-light sensitization with CuWO4 results in an enhanced photoelectrochemical response to visible light. Moreover, narrowing of the band gap (from 2.88 to 2.47 eV) with a prolonged impregnation time is also observed.

3D-Structured Metal Oxide/Sulfur Composites for High Performance Lithium-Sulfur Batteries

The lithium-sulfur (Li-S) system is one of the promising rechargeable battery systems for energy storages and electrification of vehicles due to a high theoretical capacity and energy density, as well as the low cost and availability of non-toxic sulfur. However, polysulfide dissolution is the main limitation to the stability of the Li-S system. Here, we tackle this challenge by synthesizing 3D-structured graphene and porous silica materials with a pomegranate-like architecture through a simple chemical reactions, which is subsequently loaded with sulfur to form a 3D-graphene-sulfur composite (denoted as S@G composite). Furthermore, a thin layer (~100 nm) of tungsten oxide (WO3) on the S@G composite dramatically improves the cycling performance of the Li-S system with an initial capacity of 1425 mAh/g and approximately 95% capacity retention after 500 cycles. The porous silica/sulfur composite cathodes exhibit excellent electrochemical performances including a high specific capacity of 1450 mAh g-1, a reversible capacity of 82.9 % after 100 cycles at a rate of C/2 (1 C = 1672 mA g-1) and an extended cyclability over 300 cycles at 1 C-rate. Through the analysis and the theoretical calculation, results provide a novel material and approach to enhance the electrochemical performance of rechargeable Li-S batteries and sheds light on developing high-performance energy storage devices for a variety of applications.