The chemical bonding of the sulfonate group to Pt sites is unlikely to be the sole thermodynamic driving force of the specific adsorption of sulfonate group in Nafion on Pt(111), suggesting the presence of additional incentives for adsorption. The sharp lineshape of the adsorption peak with Nafion is characteristic of the disorder-to-order second order phase transition , similar to those of hydroxide adsorption in perchloric acid and in sulfate adsorption on Pt(111). Following this line of reasoning, it is likely that the CV peak in the anodic scan on Nafion coated Pt(111) in the double layer region is induced by the ordering of the sulfonate group-containing sidechains of Nafion (Scheme 1a,b), which could be driven by the van der Waals interactions among the hydrophobic side chains and backbones. Another possibility is that the solvation environment of sulfonate groups in the hydrophobic Nafion matrix is less energetically favorable than those in liquid electrolyte, so that it is more thermodynamically favorable to stabilize them via bonding with the Pt surface. The desorption peak of sulfonate in the cathodic scan is 0.06 V lower than that in the anodic scan and exhibits a much broader lineshape (Figure ), indicating that the adsorption and desorption processes are different on the molecular level. The distinct CV features for the adsorption and desorption of the sulfonate group in Nafion on Pt(111) are quite unique, as other specifically adsorbing anions typically exhibit relatively reversible CV features for adsorption and desorption, e.g., hydroxide (Figure , black trace), sulfate and acetate . Thus, insights into the adsorption and desorption processes of the sulfonate group in Nafion could hold the key to understanding electrochemical processes at the Pt(111)/Nafion interface.