Preparations And Properties Study Of Pt-based Intermetallic Compound For Enhanced Oxygen Reduction Activity And Durability

Due to its many advantages such as high-energy conversion efficiency,environment-friendly and low operating temperature,Proton exchange membrane fuel cells（PEMFCs）are receiving more attention.However,the Pt/C catalyst widely used in cathodic oxygen reduction（ORR）also has problems such as high price,toxic and insufficient durability,which seriously restricts the development of PEMFC.Therefore,there is an urgent need to develop an efficiently Pt-based ORR catalyst,which can reduce the amount of Ptwhile improving battery performance.Due to the ordered arrangement of atoms,the ordered Pt-based intermetallic compounds show excellent catalytic activity and stability,and reduce the amount of Pt.In this paper,Pt-based ordered intermetallic compound catalysts are used as research objects.The structure,composition,and formation temperature of the catalyst are explored and regulated.Highly active and stable Pt-based intermetallic compounds are designed and synthesized The ORR activity,durability and influence of various factors of the catalyst,the main results obtained in the paper are as follows:（1）Ordered Pt₃Co/C and PtCo/C intermetallic compounds uniformly supported on the carbon support were prepared by the carbonyl cluster compound method under high temperature heat treatment.The XPS results show that the formation of ordered intermetallic compounds will lead to a decrease in binding energy and increase the degree of alloying.The electrochemical performance tests indicated that the activity of O-Pt₃Co/C is higher than that of O-PtCo/C,and the mass specific activity and area specific activity of O-Pt₃Co/C catalyst at 0.9V have reached 225.4 m A mg_Pt^-1 And 1.95m A cm^-2,which are 2.0 times and 6.3 times of JM-Pt/C,respectively.In the stability test,the O-Pt₃Co/C catalyst exhibited enhanced durability with the mass specific activity decreased only 24.5%after accelerated durability test,compared with JM-Pt/C and D-Pt₃Co/C decreased by 51.2%and 38.5%,respectively.This increase in activity and stability can be attributed to the high stability of ordered structures and changes in electronic structure.（2）In order to further reduce the amount of Pt,PtNi alloy catalysts were prepared at different heat treatment temperatures to explore the relationship between ordered PtNi intermetallic formation temperature and performance.Through the electrochemical activity test of each catalyst,it was found that the PtNi intermetallic compound formed at 650℃showed excellent ORR performance,and the mass specific activity and area specific activity of PtNi-650 catalyst at 0.9V were 242.6 m A mg_Pt^-1and 2.13 m A cm^-2,respectively.In addition,PtNi/C-650 also showed good stability.After accelerated durability test,its mass specific activity decreased by only 26.1%,while the PtNi/C-300 catalyst decreased by 41.6%.The high activity and stability of ordered PtNi/C intermetallic compounds are mainly due to the high degree of alloying and structural stability.（3）In order to further solve the problem of insufficient stability caused by the transition metal dissolution,based on the research results of Pt₃Co intermetallic compounds,nitrogen-doped Pt₃Co intermetallic compounds（O-Pt₃CoN/C）were prepared.Both the XPS and EDS confirm the successful N-doping within the Pt₃Co intermetallic compound and carbon.Electrochemical tests indicate that the decreasing order of ORR activities of the prepared catalysts are as follows:O-Pt₃CoN/C(275.7m A mg_Pt^-1)>O-Pt₃Co/N-C(249.7 m A mg_Pt^-1)>O-Pt₃Co/C(225.4 m A mg_Pt^-1)>JM-Pt/C(114.3 m A mg_Pt^-1).Stability test results show that the nitrogen doping improves the stability of the catalyst,the mass specific activity of the O-Pt₃CoN/C catalyst decreased by only 21.5%after the activity durability test,and the formation of Co-N bonds effectively prevent cobalt dissolution.The enhanced of activity and durability can be attributed to the effect of nitrogen doping on the electronic structure and the stabilizing effect of Co-N bond formation on transition metals.