Shape and composition evolution of Pt and Pt3M 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 Pt3M (M = Ni, Co) nanocrystals by hydrochloric acid (HCl) etching. As a result, only Pt3Ni nanocrystals successfully formed unsaturated step-like atoms on the surface and then constructed high-index facets (HIFs), while Pt and Pt3Co preserved a good octahedron shape. Density functional theory (DFT) calculation suggests that Cl− ions can be tightly adsorbed on the surface of Pt3Ni 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.