Simulated Volcano Plot of Oxygen Reduction Reaction on Stepped Pt Surfaces

Local activity of oxygen reduction reaction (ORR) at the middle of the (111)-terraces on n(111)×(111) Pt surfaces (n=6, 8, 10, 12 and ∞) are examined by using a DFT-based kinetic mean field model. Calculations indicate that solvation stabilization energies of all related reaction intermediates, O, OH and HO2 adsorbates, decrease with the decrease in the terrace width n, and their formation rates are decelerated by the destabilizations while their removals are accelerated. Because of the trade-off relationship between the formation and removal rates, the local ORR activity exhibits a maximal point versus the terrace width n, and the trend can be summarized in a volcano-plot versus the OH formation potential similarly to the ORR activity on alloy surfaces. The theoretically-obtained results qualitatively agree with the experiments and indicate the significance of solvation effects for designing highly active and durable cathode catalysts for polymer electrolyte fuel cells.