Anion-Catalyzed Active Dissolution Model for the Electrochemical Adsorption of Bisulfate, Sulfate, and Oxygen on Gold in H2SO4 Solution

Several plausible mechanisms for the potential-dependent adsorption of bisulfate, sulfate, and oxygen on polycrystalline gold in H 2 SO 4 (0.5 M) were evaluated, based on their fit to the experimental potentio dynamic polarization data using the anion-catalyzed active dissolution model (dc portion). The mechanism giving the best preliminary fit was further analyzed by modelling the electrochemical impedance spectroscopy data collected at various dc potentials in the electric double-layer and pre-oxide formation regions. Electrochemical quartz-crystal microgravimetry and optical ellipsometry provided additional evidence verifying the electrochemical adsorption of solution species on the gold surface. Surprisingly, dissolution was observed throughout the whole potential range under study, despite the electrode surfaces developing significant oxygen surface coverages. Key features of the experimental fractional surface coverages and current density were reproduced by the anion-catalyzed active dissolution model.