Study On The Preparation And Hydrogen Evolution Catalysis Properties Of Carbon-rich Porous SiC/WC/C-based Nanocomposite Ceramic By Polymer-derived Ceramic Approach

Tungsten carbides(WC,W2C)with the advantages of high natural abundance,easy preparation and high catalytic activity are considered as potential substitutes for precious metal catalysts due to their unique Pt like electronic structures,which can solve the problem that Pt,Pd and other precious metals can not be industrialized due to their high cost.Therefore,tungsten carbides are considered as important candidate catalytic materials for electrochemical hydrogen evolution(HER)which is the key semi-reaction of electrochemical water splitting for hydrogen production.However,their catalytic activity is still far away from commercial requirement.How to design the material structure to obtain high specific surface area of nano tungsten carbides and to improve catalytic performance has become the focus of HER catalyst materials in recent years.Polymer-derived ceramic(PDC)approach is advanced and versatile for preparing silicon-based nano ceramics.The special technological process makes it convenient and efficient to prepare micro/mesoporous ceramics with high specific surface area and excellent corrosion resistance as catalyst carrier.Therefore,a series of W-containing single-source-precursors were prepared by using allylhydridopolycarbosilane(AHPCS)as matrix,polystyrene(PS)as porogen,tungsten hexachloride(WCl6)or isopropanol tungsten {W[OCH(CH3)2]6} as tungsten sources,divinylbenzene(DVB)as carbon rich source to improve electrical conductivity of the ceramic materials.Carbon-rich porous SiC-based nanocomposite ceramics with high specific surface area were prepared via PDC approach,showing good catalytic activity for HER.The main conclusions are as follows:1)Carbon-rich porous SiC/WC/C nanocomposite ceramics were synthesized by using WCl6 as tungsten source.The molecular structural evolution of the precursors was studied by Fourier transform infrared spectroscopy(FI-IR).The phase composition and microstructural evolution of the ceramics were studied by X-ray diffraction(XRD)and transmission electron microscope(TEM),and the nanostructure characteristics were confirmed.The mesoporous characteristics were proven by Brunauer-EmmettTeller(BET)specific surface area test.The results show that the sample annealed at 1400℃ still has a high specific surface area(209.6 m2/g)due to the overflow gas of carbothermal reduction reaction.The overpotential of the sample annealed at 1400℃is 289 mV at a current density of 10 mA/cm2.2)With the similar procedure,carbon rich porous SiC/W2C/C nanocomposite ceramics were synthesized by replacing WCl6 with W[OCH(CH3)2]6.Similarly,the molecular structure evolution of the precursor was studied by FI-IR.The XRD results show that the controllable phase transition from WC to W2C was achieved by replacing WCl6 with W[OCH(CH3)2]6.The BET specific surface area test proved the mesoporous properties of ceramics,and the specific surface area of the ceramic increases slowly even at a high annealing temperature of 1500℃.Finally,the HER catalytic performance of the ceramic material was significantly improved with η10=169 mV,which confirmed that SiC/W2C/C-based nanocomposite ceramics have excellent catalytic performance for HER.