Study On The Controllable Synthesis And Electrocatalytic Performance Of Heterojunction Catalytic Materials Derived From Tungsten-based Polyoxometalate

The heavy use of non-renewable fossil fuels not only causes energy depletion,but also causes serious environmental pollution.Hydrogen energy has become a renewable energy alternative to traditional fossil fuels due to its advantages of environmental protection and high calorific value.Hydrogen production by electrolysis of water is an effective hydrogen production method,the precious metal platinum is an efficient hydrogen production catalyst,but its high price and scarce reserves limit the large-scale application of industrial hydrogen production.Therefore,it is urgent to develop non-precious metal catalysts that are economical,cheap,rich in reserves,and excellent in performance.Tungsten-based composite materials have broad application prospects in hydrogen（oxygen）evolution reactions due to their advantages such as large reserves,low cost,high activity,and good stability.In this paper,a series of highly efficient tungsten-based composite materials are designed for hydrogen evolution reaction using tungsten-based polyoxometalate as the precursor and controlled at the molecular level.The results obtained are as follows:（1）Take Finke-type polyoxometalate molecule K₁₀[Co₄（H₂O）₂(PW₉O₃₄)₂]·20H₂O(referred to as Co₄(PW₉O₃₄)₂)as the precursor,hydroxylated multi-walled carbon nanotubes as the carrier,and dicyandiamide as a nitrogen dopant.The solid phase grinding method and pyrolysis method were used to synthesize Co₂P/WC/NHCNTs heterojunction catalyst.The structure and composition of the catalyst were analyzed by IR,XRD,TEM,XPS,Raman,BET,XAS and other characterization methods.And used it as an electrode material,explored its hydrogen evolution performance.The results show that the Co₂P/WC/NHCNTs catalyst has excellent electrocatalytic hydrogen evolution activity and outstanding stability in 0.5 mol·L^-1H₂SO₄ solution,1 mol·L^-1 KOH solution,1 mol·L^-1 phosphate buffered saline solution（PBS solution）and real seawater systems.（2）Using Finke-type polyoxometalate Co₄(PW₉O₃₄)₂ as the precursor,through ZIF-8confinement(Co₄(PW₉O₃₄)₂@ZIF-8 obtained by room temperature synthesis method),hydroxylated multi-walled carbon nanotubes are anchored and dispersed,and dicyandiamide is a nitrogen dopant,and a high-activity Co₂P/WC@NC/NHCNTs heterojunction catalyst is prepared by one-step pyrolysis in N₂ atmosphere.In addition,Co₂P/WC@NC/NHCNTs was used as cathode material and anode material to explore its hydrogen evolution performance and oxygen evolution performance.It needs an overpotential of 198 m V to reach a hydrogen evolution current density of 10 m A cm^-2 in alkaline solution,the Tafel slope is 65 m V·dec^-1.If this material is used as a catalyst for oxygen production by electrolysis of water,the corresponding overpotential is 0.37 V at a current density of 10 m A·cm^-2,indicating that the strategy of confinement,anchoring,dispersion,and nitrogen doping can produce highly active electrocatalyst.（3）Using Finke-type polyoxometalate Co₄(PW₉O₃₄)₂ as the precursor,adding ammonium molybdate to play the role of molybdenum doping,through ZIF-8 confinement（room temperature synthesis method）,and then under N₂ atmosphere,highly active Co₂P/WC/Mo₂C@NC-2 tri-heterojunction was prepared through one-step pyrolysis.Co₂P/WC/Mo₂C@NC-2 was used as the cathode material to explore its hydrogen evolution performance.The results indicate that the Co₂P/WC/Mo₂C@-2 catalyst exhibits remarkable electrocatalytic hydrogen evolution performance and stability.In alkaline solution,when the current density reaches 10 m A·cm^-2,the corresponding overpotential is 180 m V,the tafel slope is 80 m V·dec^-1,indicating that molybdenum doping,ZIF-8 confinement can improve the catalytic performance of the catalyst.