, where U Pt OH and U Pt HO 2 are the redox potentials on the Pt(111) surface. Consequently, the ORR current density j relative to Pt(111) can be expressed as a function of the single variable ∆U OH = U OH -U Pt OH . As shown in Fig. , this model provides results that are in good agreement with experiments, predicting that the relative change in ORR current density j compared to that on Pt(111) exhibits a volcano-type correlation with the change in redox potential ∆U OH .