While the Nafion does not impact the Hupd region of the CV on Pt(111), it has a pronounced impact on the nature and properties of adsorbed hydroxyl species at potentials above 0.84 V (Figure ). (Figure ). This is consistent with the expectation that specifically adsorbed sulfonate groups compete with OHnormal for surface Pt sites. Further, the presence of adsorbed sulfonate impacts the property of a subset of surface Pt(111) sites, which give rise to OHNafion. More quantitatively, charges attributed to adsorbed sulfonate, OHnormal, and OHNafion based on integrated areas of CV peaks show that for every adsorbed sulfonate group on Pt(111), ~2.9 less OHnormal are present and ~1.9 OHNafion are created (Figures and). The total charge attributable to anion (OH -and sulfonate) specific adsorption remains largely unchanged when the sulfonate coverage varies from 0.022 ML to 0.048 ML (Figure ), suggesting that the adsorption of a sulfonate group loses the same amount of charge as a hydroxyl. These results also entail that adsorbed sulfonate has two types of surface footprints, i.e., area of exclusion and area of influence. The former is the footprint of site blocking, similar to many anions with tendencies to covalently bind to metal surfaces , while the latter is unique for sulfonate groups in Nafion. Adsorbed sulfonate groups are able to influence adjacent surface Pt sites in such a manner that these Pt sites are available for OH adsorption but the adsorbed OH exhibits distinct properties from those on Pt(111) devoid of adjacent adsorbed sulfonate.