Elucidation of Electrochemical Platinum Oxidation in the Presence of Halogen Anions at the Molecular Level

Electrochemical oxidation of a platinum (Pt) surface in the presence of halogen anions (X– = Cl–, Br–, I–) is significant for kinetically understanding Pt electrocatalyst dissolution. Unfortunately, the molecular fingerprints and roles of surface intermediates in Pt dissolution remain ambiguous. Here, we characterized the surface species at the intermediate stages of electrochemical Pt oxidation in the presence of X– by in situ electrochemical surface-enhanced Raman spectroscopy and density functional theory simulations. The fingerprints from surface Pt halides and hydroxide intermediates were identified. The surface complexes produced from insoluble Pt-X and soluble Pt-Xδ+ were described in detail. The pH- and X–-concentration-dependent measurements showed that an acidic electrolyte with concentrated halogen anions favored the formation of surface Pt halides. In contrast, surface Pt hydroxides were dominant in the alkaline electrolyte with diluted halogen anions. The thermodynamic competition between the formation of surface Pt halides and hydroxides is pivotal in Pt dissolution.