Preparationof Platinum-based Catalysts And Study Of Oxygen Reduction Reaction Catalytic Performances For Fuel Cells

With the extensive use of fossil energy,environmental problems have become a hot issue.It is necessary to develop new energy and find a good energy conversion device for solving the environmental problems.Proton exchange membrane fuel cells(PEMFC)have attracted increasing attention due to their high energy conversion efficiency,high current density and low pollution.However,the kinetics of oxygen reduction reaction(ORR)is slow at the fuel cell cathode,so we need to find suitable catalysts to improve the catalytic reaction efficiency.At present,the most active catalyst used in PEMFC is the precious metal Pt,which has low reserves,high price and high loding,which is limited the commercial use of fuel cells.However,the catalysts that have been commercialized still face the problems of poor stability and low utilization of platinum.Therefore,it is an urgent problem to design and develop Pt based catalysts with low Pt loading and high catalytic activity.At present,the catalysts designed to solve the above problems mainly include non-platinum catalysts,platinum nanoparticles,platinum alloy nanoparticles,core-shell platinum alloys and large octahedral alloys.The core-shell structure and alloy catalysts have been proved to be an effective method to improve the utilization of Pt and reduce the cost of catalyst.In this paper,two core-shell structure catalysts and two ordered alloy catalysts were designed and synthesized,providing theoretical reference for high efficiency fuel cell.The research of this paper mainly includes the following four aspects:1.With Pd based catalyst as the research background,PdFe/C core was first synthesized and modified by removing the excess Fe elements on the surface,exposing more Pd elements to improve the stability of the inner core.PdFe@Pt/C catalyst was prepared by microwave-assisted reduction method.With the physical characterization,the prepared PdFe@Pt/C and M-PdFe@Pt/C catalysts had small particle size and were highly distributed on the carbon support.After loading the Pt atom,the particle size of the obtained PdFe nanoparticles increased,which proved the successful loading of the Pt atom is on the surface.Electrochemical tests show that the preparation of PdFe@Pt/C and M-PdFe@Pt/C catalyst activities were higher than the commercially JM Pt/C catalyst,because the synergetic effect of Fe and Pd can improve the catalytic activity of catalysts,and with weak acid further to modify the PdFe cores,removing the surface excess Fe atoms increases the stability and the active sites of Pt.The M-PdFe@Pt/C catalyst showed good application prospects.It is mainly attributed to the control of particle size,core-shell modified structure and Pt surface electronic characteristics of the prepared catalysts.2.The Pd@Pt/C core-shell catalyst was prepared with Pd as the cores.At first,the Pd/C cores were synthesized by sodium borohydride reduction method under room temperature.Then the Pd@Pt/C catalyst was prepared by microwave-assisted reduction method.And the transition metal Au and Cr were used to doping the surface and near surface of Pd@Pt/C,and the high activity and stability of Au-Pd@Pt/C and Cr-Pd@Pt/C core-shell catalysts were obtained.The physical characterization showed that the prepared catalyst had small particle size and uniform dispersion.With the electrochemical characterization,the catalytic performance of the modified Au-Pd@Pt/C and Cr-Pd@Pt/C was higher than that of Pd@Pt/C and JM Pt/C.Two kinds of Pd@Pt/C catalysts with surface stability and shell modification were synthesized.The shell modification can effectively protect the core,while the core of Pd can well regulate the electronic structure characteristics of the outer Pt layer,so as to improve the ORR activity and stability of the catalyst.The surface and near-surface doping can significantly improve the catalytic activity of the catalyst,showing a certain application prospect.3.With the ordered PtCo/C catalyst as the research background.We synthesized the modified PtCo/C catalysts.Firstly,the atom ratio of Pt and Co is 1:1.Ordered PtCo/C catalyst was synthesized by impregnation reduction and programmed annealing,and then the surface was modified with transition metal Au and Cr.Au-PtCo/C ordered catalyst was synthesized by surface spontaneous displacement method,and Cr-PtCo/C ordered catalyst was prepared by sodium borohydride reduction method at room temperature.According to the physical characterization,the doping catalyst has little effect on the ordered structure,and the original ordered structure is retained.The Cr-PtCo/C and Au-PtCo/C catalysts obtained by surface doping showed excellent ORR catalytic activity,because the doping catalysts have more catalytic active sites and decreased binding energy,which is the main reason to improve the catalytic ORR activity.The addition of Au can improve the antioxidant potential of PtCo,so as to improve its stability.According to the configuration of the outermost electron orbital,both Au and Cr can provide electrons for Pt,thus changing the electronic characteristics of the surface Pt atom,which can increase the ORR activity.4.With the ordered PtCo catalyst as the research background,the ordered structure of PtCo/C catalyst was optimized with the third metal element.The addition of the third metal element can better regulate the electronic structure of the surface Pt atom and improve the stability of the catalyst.Firstly,by introducing different proportions of Cu atoms into PtCo/C ordered alloy system,the electronic structure of the surface can be better regulated,and the PtCoxCu1-x/C series catalysts show excellent ORR catalytic activity.The best catalytic activity was obtained when the ratio of Co:Cu=3:1.This good catalytic activity is attributed to the introduction of the third metal Cu and the formation of ordered structure.At the same time,the preparation method is simple,and the preparation process is stable.