Showing papers on "Tungsten published in 2022"

Ultrahigh Photocatalytic CO2 Reduction Efficiency and Selectivity Manipulation by Single‐Tungsten‐Atom Oxide at the Atomic Step of TiO2

Abstract: The photocatalytic CO2 reduction reaction is a sustainable route to the direct conversion of greenhouse gases into chemicals without additional energy consumption. Given the vast amount of greenhouse gas, numerous efforts have been devoted to developing inorganic photocatalysts, e.g., titanium dioxide (TiO2), due to their stability, low cost, and environmentally friendly properties. However, a more efficient TiO2 photocatalyst without noble metals is highly desirable for CO2 reduction, and it is both difficult and urgent to produce selectively valuable compounds. Here, a novel “single‐atom site at the atomic step” strategy is developed by anchoring a single tungsten (W) atom site with oxygen‐coordination at the intrinsic steps of classic TiO2 nanoparticles. The composition of active sites for CO2 reduction can be controlled by tuning the additional W5+ to form W5+–O–Ti3+ sites, resulting in both significant CO2 reduction efficiency with 60.6 μmol g−1 h−1 and selectivity for methane (CH4) over carbon monoxide (CO), which exceeds those of pristine TiO2 by more than one order of magnitude. The mechanism relies on the accurate control of the single‐atom sites at step with 22.8% coverage of surface sites and the subsequent excellent electron–hole separation along with the favorable adsorption–desorption of intermediates at the sites.

Electronically Engineering Water Resistance in Methane Combustion with an Atomically Dispersed Tungsten on PdO Catalyst.

Abstract: Improving the low-temperature water-resistance of methane combustion catalysts is of vital importance for industrial applications and it is challenging. A stepwise strategy is presented for the preparation of atomically dispersed tungsten species at the catalytically active site (Pd nanoparticles). After an activation process, a Pd-O-W1-like nanocompound is formed on the PdO surface with an atomic scale interface. The resulting supported catalyst possesses much stronger water resistance than the conventional catalysts for methane combustion. The integrated characterization results confirm that catalytic combustion of methane involves water, proceeding via a hydroperoxyl-promoted reaction mechanism on the catalyst surface. The results of density functional theory calculations indicate an upshift of the d-band center of palladium caused by electron transfer from atomically dispersed tungsten, which greatly facilitates the adsorption and activation of oxygen on the catalyst.

Optimizing Hydrogen Adsorption by d–d Orbital Modulation for Efficient Hydrogen Evolution Catalysis

Abstract: Unraveling the essence of hydrogen adsorption and desorption behaviors can fundamentally guide catalyst design and promote catalytic performance. Herein, the regulation of hydrogen adsorption is systematically investigated by d–d orbital interaction of metallic tungsten dioxide (WO2). Theoretical simulations show that the incorporation of post‐transition metal atoms including Fe, Co, Ni, and Cu can gradually reduce the bond order of W—M sites, consequently weakening the hydrogen adsorption and accelerating the hydrogen evolution reaction (HER) process. Under that theoretical guidance, various 3d metal doped WO2 electrocatalysts are systematically screened for HER catalysis. Among them, the Ni‐WO2/nickel foam exhibits an overpotential of 41 mV (−10 mA cm−2) and Tafel slope down to 47 mV dec−1 representing the best tungsten‐based HER catalysts so far. This work demonstrates that optimizing hydrogen adsorption via d–d orbital modulation is an effective approach to developing efficient and robust catalysts.

Isostatic Hot Pressed W–Cu Composites with Nanosized Grain Boundaries: Microstructure, Structure and Radiation Shielding Efficiency against Gamma Rays

Abstract: The W–Cu composites with nanosized grain boundaries and high effective density were fabricated using a new fast isostatic hot pressing method. A significantly faster method was proposed for the formation of W–Cu composites in comparison to the traditional ones. The influence of both the high temperature and pressure conditions on the microstructure, structure, chemical composition, and density values were observed. It has been shown that W–Cu samples have a polycrystalline well-packed microstructure. The copper performs the function of a matrix that surrounds the tungsten grains. The W–Cu composites have mixed bcc-W (sp. gr. Im 3¯ m) and fcc-Cu (sp. gr. Fm 3¯ m) phases. The W crystallite sizes vary from 107 to 175 nm depending on the sintering conditions. The optimal sintering regimes of the W–Cu composites with the highest density value of 16.37 g/cm3 were determined. Tungsten–copper composites with thicknesses of 0.06–0.27 cm have been fabricated for the radiation protection efficiency investigation against gamma rays. It has been shown that W–Cu samples have a high shielding efficiency from gamma radiation in the 0.276–1.25 MeV range of energies, which makes them excellent candidates as materials for radiation protection.

Interfacial engineering of Ni(OH)2 on W2C for remarkable alkaline hydrogen production

Abstract: Promoting water dissociation kinetics and hydrogen desorption ability is the key challenge of tungsten carbides for boosting hydrogen evolution reaction (HER) in alkali environment. Here, we report that an interfacial engineered W2C–Ni(OH)2 electrocatalyst consisting of Ni(OH)2 layer-encapsulated W2C nanowire array can afford current densities of 10 and 100 mA cm−2 with overpotentials of only 60 and 213 mV in 1.0 M KOH, respectively, which not only surpasses the most previously reported W2C-based examples, but even outperforms the commercial Pt/C catalyst at high current densities. The experimental results based on the classic bifunctional mechanism suggest that Ni(OH)2 mainly acts as the scissors for the dissociation of water, and the W2C site serves as the location for the adsorption and desorption of hydrogen. Further density functional theory calculations reveal that the hybridization of W2C with Ni(OH)2 can also alleviate the strong tungstenhydrogen bond, further optimizing the hydrogen adsorption energy of the hybrid.

Interfacial engineering of Ni(OH)2 on W2C for remarkable alkaline hydrogen production

Abstract: Promoting water dissociation kinetics and hydrogen desorption ability is the key challenge of tungsten carbides for boosting hydrogen evolution reaction (HER) in alkali environment. Here, we report that an interfacial engineered W2C–Ni(OH)2 electrocatalyst consisting of Ni(OH)2 layer-encapsulated W2C nanowire array can afford current densities of 10 and 100 mA cm−2 with overpotentials of only 60 and 213 mV in 1.0 M KOH, respectively, which not only surpasses the most previously reported W2C-based examples, but even outperforms the commercial Pt/C catalyst at high current densities. The experimental results based on the classic bifunctional mechanism suggest that Ni(OH)2 mainly acts as the scissors for the dissociation of water, and the W2C site serves as the location for the adsorption and desorption of hydrogen. Further density functional theory calculations reveal that the hybridization of W2C with Ni(OH)2 can also alleviate the strong tungsten hydrogen bond, further optimizing the hydrogen adsorption energy of the hybrid.

Thermal migration towards constructing W-W dual-sites for boosted alkaline hydrogen evolution reaction

Abstract: Tungsten carbides, featured by their Pt-like electronic structure, have long been advocated as potential replacements for the benchmark Pt-group catalysts in hydrogen evolution reaction. However, tungsten-carbide catalysts usually exhibit poor alkaline HER performance because of the sluggish hydrogen desorption behavior and possible corrosion problem of tungsten atoms by the produced hydroxyl intermediates. Herein, we report the synthesis of tungsten atomic clusters anchored on P-doped carbon materials via a thermal-migration strategy using tungsten single atoms as the parent material, which is evidenced to have the most favorable Pt-like electronic structure by in-situ variable-temperature near ambient pressure X-ray photoelectron spectroscopy measurements. Accordingly, tungsten atomic clusters show markedly enhanced alkaline HER activity with an ultralow overpotential of 53 mV at 10 mA/cm2 and a Tafel slope as low as 38 mV/dec. These findings may provide a feasible route towards the rational design of atomic-cluster catalysts with high alkaline hydrogen evolution activity.

CO2 Hydrogenation to Methanol on Tungsten-Doped Cu/CeO2 Catalysts

Abstract: The catalytic hydrogenation of CO2 to methanol depends significantly on the structures of metal-oxide interfaces. We show that doping a high-valency metal, viz. tungsten, to CeO2 could render improved catalytic activity for the hydrogenation of CO2 on a Cu/CeW0.25Ox catalyst, whilst making it more selective towards methanol than the undoped Cu/CeO2. We experimentally investigated and elucidated the structural-functional relationship of the Cu/CeO2 interface for CO2 hydrogenation. The promotional effects are attributed to the irreversible reduction of Ce4+ to Ce3+ by W-doping, the suppression of the formation of redox-active oxygen vacancies on CeO2, and the activation of the formate pathway for CO2 hydrogenation. This catalyst design strategy differs fundamentally from those commonly used for CeO2-supported catalysts, in which oxygen vacancies with high redox activity are considered desirable.

Tungsten nanoparticle anchoring on boron nitride nanosheet-based polymer nanocomposites for complex radiation shielding

Abstract: The synergistic effect cooperation of hybrids composed of 2D materials and metal nanoparticles have been studied extensively due to their exotic properties leading to various technological applications. We prepared tungsten nanoparticles (W NPs) decorated on boron nitride nanosheets (BNNS) hybrids and demonstrated the enhanced properties of their polyethylene (PE) nanocomposites. The uniformly decorated W NPs on the BNNS surface improved the performance by maximizing the specific surface area of the hybrids by suppressing the restacking of BNNS and aggregation of NPs. The W-BNNS/PE nanocomposites showed enhanced mechanical properties (16.4% higher yield strength and 58.1% higher elastic modulus than pure PE) and conductivity (35% higher through-plane conductivity than pure PE) due to the synergistic effects of nanoparticle anchoring and interconnection. The nanocomposites exhibited outstanding radiation shielding ability for neutron ray (4.80 cm2/g) and gamma (γ) ray (0.093 cm2/g) radiation. The results suggest that nanocomposites containing W-BNNS hybrids have good potential for application as complex radiation shielding materials.

Modulating heterointerfaces of tungsten incorporated CoSe2/Co3O4 as highly efficient electrocatalyst for overall water splitting

Abstract: Electrochemical water-splitting is rising as the promised pathway to produce pure and green hydrogen. However, the sluggish kinetics of the oxygen evolution reaction (OER) and slow reaction rate of hydrogen...

Ionically Conductive Tunnels in h‐WO3 Enable High‐Rate NH4 + Storage

Abstract: Compared to the commonly applied metallic ion charge carriers (e.g., Li+ and Na+), batteries using nonmetallic charge carriers (e.g., H+ and NH4+) generally have much faster kinetics and high‐rate capability thanks to the small hydrated ionic sizes and nondiffusion control topochemistry. However, the hosts for nonmetallic charge carriers are still limited. In this work, it is suggested that mixed ionic–electronic conductors can serve as a promising host for NH4+ storage. Using hexagonal tungsten oxide (h‐WO3) as an example, it is shown that the existence of ionic conductive tunnels greatly promotes the high‐rate NH4+ storage. Specifically, a much higher capacity of 82 mAh g–1 at 1 A g–1 is achieved on h‐WO3, in sharp contrast to 14 mAh g–1 of monoclinic tungsten oxide (m‐WO3). In addition, unlike layered materials, the insertion and desertion of NH4+ ions are confined within the tunnels of the h‐WO3, which minimizes the damage to the crystal structure. This leads to outstanding stability of up to 200 000 cycles with 68% capacity retention at a high current of 20 A g–1.

Niobium Tungsten Oxides for Electrochromic Devices with Long-Term Stability.

Abstract: There is a keen interest in the use of electrochromic materials because they can regulate light and heat, thereby reducing the cooling and heating energy. However, the long response time, short cycle life, and high power consumption of an electrochromic film hinder its development. Here, we report an electrochromic material of complex niobium tungsten oxides. The Nb18W16O93 thin films in the voltage range of 0 to -1.5 V show good redox kinetics with the coloration time of 4.7 s and bleaching time of 4.0 s, respectively. The electrochromic device based on the Nb18W16O93 thin film has an optical modulation of 53.1% at a wavelength of 633 nm, with the coloration efficiency of ∼46.57 cm2 C-1. An excellent electrochemical stability of 78.1% retention after 8000 cycles is also achieved. These good performances are due to the fast and stable Li-ion intercalation/extraction in the open framework of Nb18W16O93 with multiple ion positions. Our work provides a strategy for electrochromic materials with fast response time and good cycle stability.

Thermal migration towards constructing W-W dual-sites for boosted alkaline hydrogen evolution reaction

Abstract: Tungsten carbides, featured by their Pt-like electronic structure, have long been advocated as potential replacements for the benchmark Pt-group catalysts in hydrogen evolution reaction. However, tungsten-carbide catalysts usually exhibit poor alkaline HER performance because of the sluggish hydrogen desorption behavior and possible corrosion problem of tungsten atoms by the produced hydroxyl intermediates. Herein, we report the synthesis of tungsten atomic clusters anchored on P-doped carbon materials via a thermal-migration strategy using tungsten single atoms as the parent material, which is evidenced to have the most favorable Pt-like electronic structure by in-situ variable-temperature near ambient pressure X-ray photoelectron spectroscopy measurements. Accordingly, tungsten atomic clusters show markedly enhanced alkaline HER activity with an ultralow overpotential of 53 mV at 10 mA/cm2 and a Tafel slope as low as 38 mV/dec. These findings may provide a feasible route towards the rational design of atomic-cluster catalysts with high alkaline hydrogen evolution activity.

Microstructure and Wear Characterization of the Fe-Mo-B-C—Based Hardfacing Alloys Deposited by Flux-Cored Arc Welding

Abstract: An analysis of common reinforcement methods of machine parts and theoretical bases for the selection of their chemical composition were carried out. Prospects for using flux-cored arc welding (FCAW) to restore and increase the wear resistance of machine parts in industries such as metallurgy, agricultural, wood processing, and oil industry were presented. It is noted that conventional series electrodes made of tungsten carbide are expensive, which limits their widespread use in some industries. The scope of this work includes the development of the chemical composition of tungsten-free hardfacing alloys based on the Fe-Mo-B-C system and hardfacing technology and the investigation of the microstructure and the mechanical properties of the developed hardfacing alloys. The composition of the hardfacing alloys was developed by extending the Fe-Mo-B-C system with Ti and Mn. The determination of wear resistance under abrasion and impact-abrasion wear test conditions and the hardness measurement by means of indentation and SEM analysis of the microstructures was completed. The results obtained show that the use of pure metal powders as starting components for electrodes based on the Fe-Mo-B-C system leads to the formation of a wear-resistant phase Fe(Mo,B)2 during FCAW. The addition of Ti and Mn results in a significant increase in abrasion and impact-abrasion wear resistance by 1.2 and 1.3 times, respectively.

High density of tungsten gadolinium borate glasses for radiation shielding material: Effect of WO3 concentration

Abstract: The aim of this work is to study the radiation shielding properties in the glass systems xWO3: (70-x)Gd2O3: 30B2O3 (WGB) where x = 40, 45, 50, 55, and 60 mol%. These glasses were prepared by the melt quenching techniques. The Compton scattering technique was used to measure the experimental values of the total mass attenuation coefficient (MAC), the effective atomic number (Zeff), and the electron density (Neff) at 0.223 MeV–0.662 MeV. The measured MAC, Zeff, and Neff results were compared with the simulated and theoretical values obtained from Geant4 code and WinXcom software respectively. The comparison between the experimental, simulation and theoretical approaches for the determination of the several radiation shielding factors reflects the good detection system setup of Compton scattering experiment. The density is decreased with the increasing of WO3 concentrations from 6.1868 g/cm3 to 5.2669 g/cm3 and molar volume result demonstrated non-bridging oxygen and network former in the glass structure. The MAC, Zeff, and Neff results have similar trends, which increase by adding WO3 contents, and decrease with increasing of the energies. The HVL result showed that increased at the higher WO3 concentrations. Moreover, the HVL at 40 mol % of the concentration showed the highest density, and demonstrated better efficiency when compared with some standard shielding materials.

W–Cu composites with excellent comprehensive properties

Abstract: Excellent mechanical and physical properties are usually mutually exclusive in W–Cu composites, which makes it challenging to achieve outstanding comprehensive performance. In the present work, improved copper connectivity and uniformly dispersed ultrafine tungsten particles were achieved in the ultrafine grained (UFG) W–Cu composites. The as-prepared UFG W–Cu composites exhibited enhanced combination of hardness, compressive strength and electrical conductivity compared with those reported in the literature. Specifically, the UFG W–30Cu composite showed a compressive strength over 1200 MPa (2.1 times that of the coarse grained counterpart), a hardness of 357 HV and an electrical conductivity of 48.6%IACS. The strengthening mechanisms of the presented W–Cu composites were quantitatively discussed in terms of grain refinement, stress transfer and dislocations strengthening. This study provides a novel approach for the synthesis of W–Cu composites with excellent comprehensive properties.

Underwater metamaterial absorber with impedance-matched composite

Abstract: By using a structured tungsten-polyurethane composite that is impedance matched to water while simultaneously having a much slower longitudinal sound speed, we have theoretically designed and experimentally realized an underwater acoustic absorber exhibiting high absorption from 4 to 20 kHz, measured in a 5.6 m by 3.6 m water pool with the time-domain approach. The broadband functionality is achieved by optimally engineering the distribution of the Fabry-Perot resonances, based on an integration scheme, to attain impedance matching over a broad frequency range. The average thickness of the integrated absorber, 8.9 mm, is in the deep subwavelength regime (~λ/42 at 4 kHz) and close to the causal minimum thickness of 8.2 mm that is evaluated from the simulated absorption spectrum. The structured composite represents a new type of acoustic metamaterials that has high acoustic energy density and promises broad underwater applications.

Operating a full tungsten actively cooled tokamak: overview of WEST first phase of operation

Abstract: Abstract WEST is an MA class superconducting, actively cooled, full tungsten (W) tokamak, designed to operate in long pulses up to 1000 s. In support of ITER operation and DEMO conceptual activities, key missions of WEST are: (i) qualification of high heat flux plasma-facing components in integrating both technological and physics aspects in relevant heat and particle exhaust conditions, particularly for the tungsten monoblocks foreseen in ITER divertor; (ii) integrated steady-state operation at high confinement, with a focus on power exhaust issues. During the phase 1 of operation (2017–2020), a set of actively cooled ITER-grade plasma facing unit prototypes was integrated into the inertially cooled W coated startup lower divertor. Up to 8.8 MW of RF power has been coupled to the plasma and divertor heat flux of up to 6 MW m −2 were reached. Long pulse operation was started, using the upper actively cooled divertor, with a discharge of about 1 min achieved. This paper gives an overview of the results achieved in phase 1. Perspectives for phase 2, operating with the full capability of the device with the complete ITER-grade actively cooled lower divertor, are also described.