Congruent melting of tungsten phosphide at 5 GPa and 3200℃ for growing its large single crystals

As one of important members of refractory materials,tungsten phosphide(WP)holds great potential for fundamental study and industrial applications in many fields of science and technology,due to its excellent properties such as superconductivity and as-predicted topological band structure.However,synthesis of high-quality WP crystals is still a challenge by using tradition synthetic methods,because the synthesis temperature for growing its large crystals is very stringently required to be as high as 3000℃,which is far beyond the temperature capability of most laboratory-based devices for crystal growth.In addition,high temperature often induces the decomposition of metal phosphides,leading to off-stoichiometric samples based on which the materials'intrinsic properties cannot be explored.In this work,we report a high-pressure synthesis of single-crystal WP through a direct crystallization from cooling the congruent W-P melts at 5 GPa and^3200℃.In combination of x-ray diffraction,electron microscope,and thermal analysis,the crystal structure,morphology,and stability of recovered sample are well investigated.The final product is phase-pure and nearly stoichiometric WP in a single-crystal form with a large grain size,in excess of one millimeter,thus making it feasible to implement most experimental measurements,especially,for the case where a large crystal is required.Success in synthesis of high-quality WP crystals at high pressure can offer great opportunities for determining their intrinsic properties and also making more efforts to study the family of transition-metal phosphides.

Cobalt tungsten phosphide with tunable W-doping as highly efficient electrocatalysts for hydrogen evolution reaction

It has been of interest in seeking electrocatalysts that could exercise equally high-efficient and durable hydrogen evolution upon nonselective electrolytes in both acidic and alkaline environments. Herein, we report a facile strategy to fabricate cobalt tungsten phosphides (CoxW2−xP2/C) hollow polyhedrons with tunable composition based on metal-organic frameworks (MOFs) template method. By the deliberate control of W doping, the synthesized catalyst with the composition of Co0.9W1.1P2/C is found to be able to achieve a current density of 10 mA·cm^(−2) at overpotentials of 35 and 54 mV in acidic and alkaline media, respectively. This combined electrochemical property stands atop the state-of-the-art electrocatalyst counterparts. To unveil the peculiar behavior of the structure, density functional theory (DFT) calculation was implemented and reveals that the surface W-doping facilitates the optimization of hydrogen absorption free energy (ΔGH*) as well as the thermodynamic and kinetics barriers for water dissociation, which is coupled with the hollow structure of Co-W phosphides, leading to the prominent HER catalytic performance.

Synthesis, characterization and hydrotreating performance of supported tungsten phosphide catalysts

Supported tungsten phosphide catalysts were prepared by temperature-programmed reduction of their precursors(supported phospho-tungstate catalysts)in H2 and characterized by X-ray diffraction(XRD),BET,temperature-programmed desorption of ammonia(NH3-TPD)and X-ray photoelectron spectroscopy(XPS).The reduction-phosphiding processes of the precursors were investigated by thermogravimetry and differential thermal analysis(TG-DTA)and the suitable phosphiding temperatures were defined.The hydrodesulfurization(HDS)and hydrodenitrogenation(HDN)activities of the catalysts were tested by using thiophene,pyridine,dibenzothiophene,carbazole and diesel oil as the feedstock.The TiO2,c-Al_(2)O_(3) supports and the Ni,Co promoters could remarkably increase and stabilize active W species on the catalyst surface.A suitable amount of Ni(3%–5%),Co(5%–7%)and V(1%–3%)could increase dispersivity of the W species and the BET surface area of the WP/c-Al_(2)O_(3) catalyst.The WP/c-Al_(2)O_(3) catalyst possesses much higher thiophene HDS and carbazole HDN activities and the WP/TiO2 catalyst has much higher dibenzothiophene(DBT)HDS and pyridine HDN activities.The Ni,Co and V can obviously promote the HDS activity and inhibit the HDN activity of the WP/c-Al_(2)O_(3) catalyst.The G-Ni5 catalyst possesses a much higher diesel oil HDS activity than the sulphided industrial NiW/c-Al_(2)O_(3) catalyst.In general,a support or promoter in the WP/c-Al_(2)O_(3) catalyst which can increase the amount and dispersivity of the active W species can promote its HDS and HDN activities.

Tuning electronic configuration of WP_(2) nanosheet arrays via nickel doping for high-efficiency hydrogen evolution reaction

Modulate the electronic structure and surface energy by nanostructure and heteroatom doping is an efficient strategy to improve electrocatalytic activity of hydrogen evolution reaction(HER).Herein,nickel incorporated WP_(2) self-supporting nanosheet arrays cathode was synthesized on carbon cloth(Ni-WP_(2) NS/CC)by in-situ phosphating reduction of the Ni-doped WO3.It shows that heteroatom doping and the three-dimensional(3D)nanosheet arrays morphology both facilitate to reduce the interfacial transfer resistance and increase electrochemical-active surface areas,which effectively improve electrocatalytic hydrogen evolution reaction(HER)activity.The optimized catalyst,1%Ni-WP_(2) NS/CC,exhibits an outstanding electrocatalytic performance with an overpotential of 110 m V at 10 m A cm^(-2) and a Tafel slope of 65 m V dec^(-1) in the acid solution.DFT calculations further demonstrate the nickel doping can adjust the intrinsic structure of electronics,lower the Gibbs free energy of adsorption of hydrogen(DGH*),and effectively improve the HER performance.