Understanding the Grain Boundary Behavior of Bimetallic Platinum-Cobalt Alloy Nanowires toward Oxygen Electro-Reduction

Abstract

Grain boundaries (GBs) are defects in crystal structures, which are in general known to be highly active toward various electrocatalytic reactions. Herein, we identify the adverse behaviors of the GBs for bimetallic platinum-cobalt (Pt-Co) nanocatalysts in the oxygen reduction reaction (ORR). As model catalysts, GB-rich Pt-Co nanowires (Pt-Co GB-NWs) and single-crystalline Pt-Co nanowires (Pt-Co SC-NWs) are synthesized. They have very similar diameters, Pt-to-Co ratios, and Pt-rich surface structures, except for the GB populations, which can be precisely controlled by applying an external magnetic field during their synthesis. The presence of GBs in Pt-Co NWs promotes Co leaching at an applied electrochemical potential, inducing significant changes in the surface Pt-to-Co ratio. The resulting Pt-Co GB-NWs perform only half the ORR activity compared with the Pt-Co SC-NWs. As a result, it is revealed that the surface GB sites are deactivated by causing elemental leaching and may not act as an ORR promoter for the Pt-Co nanowire catalyst.