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Oxygen Reduction and Oxygen Evolution Reaction Activity on Co/Pt(111) Surfaces in Alkaline Solution

We investigated the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity of Co and Pt bimetallic systems (n-monolayer (ML)-Co/Pt(111); n = 0.13–2.0) in 0.1 M KOH. For the ORR, the 0.25ML-Co/Pt(111) substrate showed the greatest activity enhancement: 1.7 times of that of clean Pt(111). The ORR activity enhancements were sensitive for the submonolayer-thick Co: the 0.25ML-Co/Pt(111) showed highest activity (1.7-fold vs. clean Pt(111)) and the activity steeply decreased above the Co thickness of 0.5 ML. For the OER, the activity increased with an increasing Co thickness and the 2ML-Co/Pt(111) substrate was the most active. This study suggests that the tuning of the near-surface nanostructures (e.g., Pt-Co composition ratio and chemical state of the Co-(hydro)oxide) is important for achieving high ORR and OER activity in Pt-3d-transition-metal alloy electrocatalysts under alkaline conditions.