Formation and Analysis of Core–Shell Fine Structures in Pt Bimetallic Nanoparticle Fuel Cell Electrocatalysts

An Ångstrom-scale structural and compositional investigation of a dealloyed Pt–Co core–shell nanoparticle fuel cell catalyst with characteristic diameter of 10–15 nm in an early stage of its life cycle reveals unusual self-organized compositional subsurface fine structure, that is, subsequent shells of Co depletion and enrichment. The origin of the unusual structure is rationalized by interplay of Co dissolution, Pt surface diffusion, and an inverse Kirkendall effect. A detailed picture about the chemical composition of the surface and subsurface provides a fundamental insight into the catalytically active structure of bimetallic electrocatalysts.