As the electrolyte composition has not changed, the simplest explanation is that past the anion switch potential, hence its name, hydroxyl anions are replacing chloride anions at the interface. This phenomenon can be observed in any combination of anions and cations. In the perchlorate case, the difference in the O-upd features supports previous findings that perchlorate does interact with the Pt surface , albeit much weaker than chloride. Consequently, the characteristic CV patterns are associated with anions, in decreasing order of their interactions with the H-upd: OH ->> Cl -> ClO4 -. Cations appear to have mostly secondary effects, with lithium cations having some distinct effects compared to sodium and potassium, see Fig. where the O-upd is present, but the characteristic peak is absent. We can quantify these effects by performing a peak analysis, like the one presented in Fig. . The result is presented in Fig. for which we must remind ourselves of the meaning of the peak position: The peak position, or any of the features of a CV, is a combination of reactant activities and their energy states in the form of their Gibbs free energy.