Investigation On Controlled Synthesis Of High-performance Pt-Ni Alloys Towards The ORR In Pemfcs As Well As Its Mechanism

Confronted with the increasingly serious environmental issues,proton exchange membrane fuel cells（PEMFCs）have received widely concerns for the advantages of high efficiency,high power,zero emission,and so on.However,the application of noble Pt or Pt-based alloys as the cathodic electrocatalysts for the oxygen reduction reaction（ORR）in PEMFCs results in a high fuel cell cost,thus impeding the commercialization of PEMFCs.Therefore,it is very important to develop high-performance Pt-based alloys to lower Pt loading,thus promoting the PEMFCs to the marketplace.Shape-controlled Pt-Ni alloys usually offer an exceptional activity and durability towards the ORR,and the tricks lie in their well-designed morphologies and surface compositions.In this thesis,a series of Pt-Ni alloys with special structures（like“concave”structure,“core-shell”structure,etc）or compositions（like Pt-rich“skeleton”structure,Ni-rich alloys,etc）have been developed.Their corresponding elements distribution,geometric and electronic structures are comprehensively analyzed based on various advanced physiochemical technologies.Moreover,the relations between their microstructures and the ORR activity have been well clarified.We employ a thermal annealing under H₂ to enhance the durability of a Ni-rich defective heterogeneous quasi-octahedral Pt-Ni alloy.A truncated octahedral Pt-Ni alloy with Ni O-Pt double shells structure is eventually obtained.The evolution of both surface compositions and morphologies of the defective heterogeneous quasi-octahedral Pt-Ni alloy during thermal annealing is tracked by various techniques.It is believed that the formation of truncated octahedron is an energetically favorable result while the outward segregation of oxides（Pt O_x,Ni O）driven by H₂ effects leads to the formation of Ni O-Pt double shells.On the one hand,the formed Ni O outer shell plays an important role in mitigating conglobation during thermal annealing,on the other hand,the removal of Ni O outer shell can be considered as a novel and convenient way for dealloying without destroying the particles structure.Owing to the evolution of both morphologies and compositions,the obtained core-shell Pt-Ni truncated octahedron presents a 3.4-folds mass-specific activity comparing to the unannealed sample,and its ORR activity preserve 45.4%after 30,000 potential cycles of the accelerated degradation tests.The truncated core-shell Pt-Ni octahedral catalyst based membrane electrolyte assembly（MEA）with 0.1mg _Pt/cm² Pt loading performs a high peak power density of 679.8m W/cm² under H₂/air,increased by138.4m W/cm² comparing with that of commercial Pt/C catalyst.It is very practicable to apply high-performance Pt-Ni alloys in the cathode of PEMFCs,which will greatly lower Pt loading and promote the industrialization of PEMFCs.