Migration of Cobalt Species within Mixed Platinum-Cobalt Oxide Bifunctional Electrocatalysts in Alkaline Electrolytes.

Bifunctional oxygen electrocatalysts have great potentials for energy storage and conversion applications. Here we report a facile strategy toward bifunctional electrocatalysts by supporting mixed platinum and cobalt oxide nanoparticles on carbon black. The composite electrocatalyst (denoted as Pt+CoO_x/C) is found to exhibit higher oxygen evolution reaction (OER) activity than CoO_x/C, but slightly lower oxygen reduction reaction (ORR) activity than Pt/C in alkaline electrolytes. The bifunctional catalytic performance is ascribed to the in situ formation of heterogenous platinum-cobalt (hydro)oxide (Pt-CoO_xHy) interfaces under the electrochemical reaction conditions. Calculated electrochemical phase (Pourbaix) diagrams suggest that the migration of Co species was driven by the relative stability of Pt-CoO_xHy interfaces versus bulk (hydroxy)oxides or aqueous ions of cobalt. [ABSTRACT FROM AUTHOR]