Shape and composition evolution of Pt and Pt_(3)M nanocrystals under HCl chemical etching

Controlling the shape and composition of Pt-based nanocrystals is essential to improve electrocatalytic performance.In this work,we have carefully investigated the evolution process of morphology and composition for Pt and Pt_(3)M(M=Ni,Co)nanocrystals by hydrochloric acid(HCl)etching.As a result,only Pt_(3)Ni nanocrystals successfully formed unsaturated step-like atoms on the surface and then constructed high-index facets(HIFs),while Pt and Pt_(3)Co preserved a good octahedron shape.Density functional theory(DFT)calculation suggests that Cl-ions can be tightly adsorbed on the surface of Pt_(3)Ni rather than other nanocrystals,which hinders the deposition of newly-reduced atoms and thus regulating the surface morphology.Besides,the etching of surface transitional metals further accelerates the formation of HIFs.Boosted by the active sites on the surface,HCl-Pt-Ni exhibited a~10.8 and~11.3 times higher oxygen reduction reaction(ORR)mass and specific activities than commercial Pt/C catalyst,and possessed a good durability after 10,000 cycles test.This work gives a deep insight into the design of high-performance Pt-based ORR catalysts.