Study On The Growth Mechanism And Oxygen Reduction Activity Of Pt-Ni Alloy Catalyst For Fuel Cell

Raising environmental concerns along with the deprivation of traditional energy have put an increasing demand for efficient and clean renewable energy.Proton exchange membrane fuel cell?PEMFC?,an electrochemical energy conversion technology renowned for high efficiency and zero emission,has received increasing attentions in different areas.PEMFC powered vehicles?FCVs?is considered as the most promising application.Thanks to tremendous research and development efforts in the last two decades,the PEMFC systems have met automotive performance and durability requirements,and the automakers are trying best to bring FCVs to the marketplace.However,the high Pt loading required to compensate the low oxygen reduction reaction?ORR?activity of conventional Pt catalysts leads to higher cost compared with internal combustion engines,impeding the commercialization of FCVs.Therefore,developing high activity catalysts to lower the Pt loading is necessary.The electrochemical activity of catalyst for oxygen reduction activity?ORR?is highly dependent on the shape and composition distribution of nanoparticles?NPs?.Herein,we synthesize a sandwich-structured,icosahedral Pt_2.1Ni catalyst via hot injection method in the nonhydrolytic reaction systems.Characterizations for identifying the microstructure and composition distribution of the as-synthesized nanoparticles and electrochemical measurements of ORR property were then implemented to research its growth mechanism and the corresponding influence on catalytic activity.The main conclusions have been drawn as follows:1.The as-synthesized Pt?111?enclosed Pt_2.1Ni nanoparticles have well-defined size?⁹.45nm?and shape and a unique sandwich-like structure:Pt-enriched core,Ni-enriched interlayer and Pt-enriched shell.2.The growth of Pt_2.1Ni nanoparticle is found involving three steps,i.e.,burst nucleation of Pt atoms to form Pt-enriched core,heterogeneous nucleation of Ni atoms onto Pt core to form Ni-enriched interlayer,and kinetic controlled growth of Pt-enriched shell.3.This unique sandwich structure improves the mass-and area-specific activity to 0.91 mA cm^-2 and 0.32 A8)2)^-1@0.9V?vs.RHE?,reaching 4.1and 2.5 times respectively,compared to those of the commercial Pt/C.Moreover,the Pt_2.1Ni/C also presents a remarkable catalytic stability after15 000 cycles.The controlled sandwich structure with?111?facets enclosed Pt-shell and highly uniform morphology account together for the improved electrocatalytic property.4.The Pt-enriched core protects the nanostructure from collapse and mitigate the strain change caused by lattice mismatch,and thus enhances structure stability.The Ni-enriched interlayer induces the electronic modification of the outermost Pt shell,and in turn tunes the activity.The Pt-enriched shell provides more active sites via the exposure of?111?facets and retards the dissolution of Ni atoms.This study on the growth mechanism and the consequent influence on electrocatalytic activity and stability can be further used to guide the synthesis of high-activity ORR catalyst with controllable morphology and composition distribution.