Underpotential Deposition of Copper on Au(III) Single‐Crystal Surfaces: A Voltammetric and Rotating Ring Disk Electrode Study

Abstract

The underpotential deposition of copper on Au(111) single‐crystal substrate was studied using voltammetric and rotating ring‐disk electrode measurements (RRDE) in sulfuric acid solutions of different Cu²⁺ concentrations at constant pH 1 and . Cyclic voltammograms and charge isotherms indicate that the ideal metal‐monolayer model, characterized by an electrosorption valency value of , is valid only at high degree of coverage at low underpotentials. Significant deviation from the ideal behavior was observed at high underpotentials, where the electrosorption valency was found to be . This can be interpreted in terms of a partial discharge of Cu²⁺to , the adsorption of which is stabilized by co‐adsorption of sulfate ions. Transfer of the into the solution could only be detected in the transition range from underpotential to overpotential copper deposition using RRDE measurements. The kinetics of the formation is mainly determined by the charge‐transfer reaction , rather than by the disproportionation reaction .