The well-defined single crystal surfaces affords structural certainty on the electrode side and high sensitivity toward interfacial electrochemical processes with CV, which could help elucidate the impact of surface species on the intrinsic ORR kinetics. However, the assumption that insights gained from model systems could be transferred to the real systems that they are supposed to represent must be tested. In the present case, structural complexity of the electrode surface is introduced by using a polycrytalline Pt disk, denoted as pc-Pt, to construct the electrode/Nafion interface. The ORR activity remains inversely correlated with the size of the sulfonate adsorption peak on a Nafion-covered pc-Pt (Figure ) . However, the OHNafion peak in CV on Nafion-covered pc-Pt is obscured by the broad OH adsorption and desorption peaks, despite the appearance of sulfonate adsorption and desorption peaks (Figure ), which is similar to the observation on supported Pt nanoparticles with Nafion as binder in a report . Thus, the correlation between the OHNafion peak and the ORR activity could not been identified with results on pc-Pt or supported Pt nanoparticles, which highlights the unparalleled sensitivity of experiments employing single crystal surfaces. Many different facets are present on pc-Pt, so the fact that same correlation holds at the interfaces of Nafion with Pt(111), Pt(554) and pc-Pt indicates that the two single crystal facets, i.e., Pt(111) and Pt(554), are representative of the activity trend on other facets of Pt surface. Aquivion also has a much less pronounced effect on the CV of Pt(554) and pc-Pt than Nafion, with limited impact on the ORR activity (Figures and). Results discussed above provide compelling evidence for the detrimental effect of the presence of OHNafion on the ORR activity on Pt surfaces, which are in line with existing literature .