Isotopic labeling experiments reveal that proton is required to mediate the sulfonate desorption. CV collected on Pt(111) in 0.1 M DClO4 in D2O shows the expected anodic shift of the OH adorption/desorption peak by 35 mV compared to those in H2O (Figure ), confirming the lack of impurities in D2O . Sulfonate adsorption peaks overlap in CVs collected in H2O and D2O on Nafion-covered Pt(111), while sulfonate desorption peak shifts cathodically by 20 mV in D2O compared with that in H2O (Figure ). These results