Enhancing Oxygen Reduction Reaction Activity via Pd−Au Alloy Sublayer Mediation of Pt Monolayer Electrocatalysts

New Pt monolayer electrocatalysts were prepared using galvanic displacement of a copper monolayer deposited at underpotentials on a Pd core. By performing underpotential deposition twice, two monolayers were deposited, forming a core−shell structure with double shells. The double shells consist of an outermost shell of Pt monolayer and a sublayer shell of Pd−Au alloy. It was found that by adjusting the compositions of the alloy sublayer, it is possible to mediate the oxygen reduction reaction (ORR) activity of the Pt catalysts. An alloy with 10% (atomic) Au was found to be the most active among the catalysts tested. Furthermore, the catalysts showed good cycling stability that may be due to stabilizing effect of Au. Since different alloys can be used as the sublayer for mediation, this work may open up various opportunities to tailor electrocatalysts for best ORR activity.