are sluggish (Figures 6 and S9 and S10). Thus, it is reasonable to deduce that the reduced ORR activity on Nafion-covered Pt(111) is caused by the slower *O → *OH coversion and *OH reduction on the Pt sites in the vicinity of adsorbed sulfonate groups. According to the charges attributed to adsorbed sulfonate and OHNafion in CVs (Figure ), it could be inferred that one adsorbed sulfonate could generate ~2 OHNafion species. This observation supports the hypothesis in the literature to rationalize the worse than expected performance in MEA after low humidity operation, i.e., one adsorbed sulfonate could impact the ORR activity of more than one Pt sites .