Enhanced activity for oxygen reduction reaction on Pt3CO nanoparticles:: Direct evidence of percolated and sandwich-segregation structures

Atomically resolved structures and composition of Pt alloy nanoparticles were obtained using aberration-corrected high-angle dark field imaging, which was correlated to specific ORR activity based on a Pt surface area. The enhanced specific ORR activity (similar to 2 times relative to Pt) of acid-treated Pt3Co nanoparticles can be related to composition variations at the atomic scale and the atomic scale and the formation of percolated Pt-rich and Pt-poor regions within individual particles. Upon annealing, we show direct evidence of surface Pt sandwich-segregation structures, which correspond to a specific ORR activity similar to 4 times relative to Pt.