Markovic and coworkers proposed that adsorbed OH on Pt(111) blocks surface sites available for the ORR , so that a lower spectator (OH) coverage is expected to enhance the rate. The second school of thought considers adsorbed OH as a reaction intermediate, which binds too strongly on Pt surfaces and hinders its desorption in the last elementary step of the ORR . These two theories lead to a consistent thermodynamic prediction for improving the ORR activity on Pt, i.e., reducing the OH binding energy of Pt-based materials, which has inspired a large body of recent works . Insights gained in this work at the Pt/Nafion interface are inconsistent with the aforementioned thermodynamic arguments. As shown Figure , with ~20% coverage of OHNafion, the kinetic ORR current density at 0.9 V is only ~43% of that on bare Pt(111). The presence of Nafion also reduces ~20% of charges for the total charges attributable to sulfonate and OH adsorption (Figure ), suggesting that the density of unoccupied Pt sites increases with the sulfonate adsorption. If the density of unoccupied Pt sites is the primary factor in determining the ORR activity, rates are expected to rise with Nafion adsorption, which is opposite to the observed drops in the ORR activity(Figure ). Potential for OH coverage of 1/6 ML has been employed as an experimental measure of the OH binding strength. With the adsorbed sulfonate, this potential shifts anodically compared to that on the bare Pt(111) (Figure ), suggesting that OH binding is weaker on the Nafion-covered Pt(111).