The formation and reduction of both OHNafion and ONafion are less reversible than OHnormal and Onormal, respectively. When the upper bound potential in CVs is set at 0.90 V at a scan rate of 50 mV/s, the adsorption and desorption of OHnormal are quite reversible with a negligible peak separation (Figure , black trace). In contrast, the adsorption and desorption features of OHNafion are highly asymmetrical with a peak separation of ~40 mV, suggesting the process is much less reversible than that of OHnormal (Figure ). When the scan rate is varied from 5 to 500 mV/s, the peak separations of the adsorption/desorption of both sulfonate and OHnormal remain largely unchanged (Figure ), while that of OHNafion increases from 32 to 65 mV, confirming the slower kinetics of OHNafion. Additionally, the adsorption peak of OHNafion became broader and weaker, and shifted to more positive potentials with increasing scan rate to 500 mV/s, which further suggested that OHNafion formation required a higher kinetic barrier than that of OHnormal. Similarly, slower redox kinetics was observed in the formation of ONafion than that of Onormal. The CV peak of ONafion shifted positively compared with Onormal (Figure ), indicating that the OHNafion → ONafion conversion is more sluggish on sites influenced by adjacent adsorbed sulfonate groups in Nafion. It is reasonable to deduce that the reverse process, i.e., ONafion → OHNafion, is also kinetically more sluggish than that of Onormal → OHnormal.