Preparation And Catalytic Performance Research Of Heteropoly Acid Supported Ag@pt/mwcnt Composite Catalysts

Proton exchange membrane fuel cell(PEMFC)is a new energy device that has been the focus of research in the new century.It has the advantages of high energy density,clean,and no pollution.However,the low catalytic activity and high cost of the cathode oxygen reduction catalysts have always been an important factor affecting the large-scale commercial application of proton exchange membrane fuel cells.This paper focuses on the preparation of a low platinum catalyst with high catalytic activity and low cost by loading heteropoly acids onto Ag@Pt/MWCNT core-shell catalysts.This is expected to play a promoting role in the commercial application of proton exchange membrane fuel cell.In this paper,several different heteropolyacids were successfully prepared and loaded onto Ag@Pt/MWCNT catalyst to prepare several different composite catalysts.Physical characterization of catalysts by physical characterization methods such as XRD,electron microscopy,and XPS,electrochemical characterization of its catalytic performance by cyclic voltammetry,linear sweep voltammetry and other test methods.The main work is as follows:1,Phosphomolybdicvanadic acid(PMo12-nVnO40(n=1,2,3))with Keggin structure was successfully prepared by acidification extraction method.The composite catalyst Ag@Pt/MWCNTs-PMo12-nVnO40(n=1,2,3)was prepared by loading the heteropolyacid onto Ag@Pt/MWCNTs catalyst by chemical impregnation method.Physical characterization methods such as XRD indicate that the number of different vanadium substitutions will affect the structure of heteropolyacids.The stability test and cyclic voltammetry results show that the catalytic activity of the composite catalyst has been significantly improved without affecting the stability of the composite catalyst.When the loading of three kinds of heteropolyacids is 20%,the corresponding composite catalyst has the relatively good electrochemical performance.And the change of the number of vanadium atoms in the polyacid will also affect the catalytic performance of the composite catalyst.Among them,the catalytic activity of 20%PMo10V2-Ag@Pt/MWCNTs composite catalyst is better than that of other composite catalysts under the same conditions.The electrochemical active area could reach 95.2m2/g,and the initial reduction potential could be 0.968V.The kinetics analysis shows that O2 is reduced to H2O by a direct "four-electron" reaction on the composite catalyst.2,Two kinds of Keggin structure isomers of silicon molybdenum heteropolyacids(a,P-SiMo12O40)were successfully prepared by acidification extraction method.The composite catalyst Ag@Pt/MWCNTs-???-SiMo12O40 was prepared by loading the heteropolyacid onto Ag@Pt/MWCNTs catalyst by chemical impregnation method.Physical properties such as XRD indicate that there are differences in the spatial structure between the two isomers of the silicon molybdenum heteropoly acids.The stability test and cyclic voltammetry results show that the addition of silicomolybdic heteropolyacid can effectively increase the catalytic activity of the catalyst without affecting the stability of the composite catalyst.When the loading of two isomers of silicon-molybdenum heteropoly acid is 15%,the electrochemical performance of the corresponding composite catalyst is relatively more better.The catalytic activity of the composite catalyst have been also affected with different isomer structures of silicon molybdenum heteropoly acids.Among them,the catalytic activity of Ag@Pt/MWCNTs-15%?-SiMo12O40 composite catalyst is superior to that of other composite catalysts under the same conditions.The electrochemical active area could reach 85.92m2/g,and the initial reduction potential could be 0.922V.The kinetics analysis shows that 02 is reduced to H20 by a direct "four-electron"reaction on the composite catalyst.3,Silicon-tungsten heteropolyacid(SiW12O40)was successfully prepared by acidification extraction method.The composite catalyst Ag@Pt/MWCNTs-SiW12O40 was prepared by loading the heteropolyacid onto the Ag@Pt/MWCNTs catalyst by chemical impregnation method.Physical properties such as XRD indicate that the prepared silicotungsten heteropolyacid is a Keggin structure.The stability test and cyclic voltammetry results show that the addition of silicotungsten heteropolyacid can effectively increase the catalytic activity of the catalyst without reducing the stability of the composite catalyst.When the loading of silicotungsten heteropolyacid is 20%,the electrochemical performance of the corresponding composite catalyst is relatively more better.The catalytic activity of Ag@Pt/MWCNTs-20%SiW12O40 composite catalyst is better than that of other composite catalysts under the same conditions.The electrochemical active area can reach 77.12m2/g,and the initial reduction potential can reach 0.927V.The kinetics analysis shows that O2 is reduced to H20 by a direct "four-electron" reaction on the composite catalyst.