Influence of Anion Chaotropicity on the SO ₂ Oxidation Reaction: When Spectator Species Determine the Reaction Pathway

The electrochemical SO 2 oxidation reaction (SO 2 OR) is a promising alternative to the O 2 evolution reaction for H 2 electrochemical generation. The SO 2 OR exhibits a low thermodynamic potential and small kinetic barrier, and Au has been observed to be a very active catalyst. For this material, nonlinear dynamic behavior is observed, which is related to the electrolyte chaotropicity at the solid‐liquid interface. In this work, the influence of the chaotropicity was investigated by electrochemical and spectroelectrochemical techniques, and the main reasons for the dependence on the chaotropicity were investigated. The electrochemical response as a function of the chaotropicity was determined as a function of the mechanism observed, and the reaction pathway selection was related to the intermediate adsorption, which in turn was controlled by the interfacial water structure. The “neutral” chaotropicity was found to be the optimum condition for SO 2 OR.