Durability of Pt3Co/C nanoparticles in a proton-exchange membrane fuel cell: Direct evidence of bulk Co segregation to the surface

Pt3Co/C electrocatalysts are not stable when operated in real PEMFC conditions but face variations of their chemical composition. The latter signs that Co atoms can segregate from the bulk to the surface of the nanoparticles, which we believe is activated by the formation of surface oxides and the leaching of Co at the surface. Consequently, the alloyed Pt3Co/C nanoparticles slowly evolve towards Pt shell/Pt–Co alloy core structures with depleted Co content and a Pt-enriched shell.