Underpotential deposition of Cu onto Au(111) in the presence of acetate

The underpotential deposition (UPD) of Cu on Au(111) in the presence of acetate is investigated by cyclic voltammetry, potential step experiments, and in-situ STM imaging. The specific adsorption of acetate stabilizes the UPD monolayer (ML) of Cu on Au(111). Three distinct deposition processes are identified by cyclic voltammetry. The first two deposition processes corresponding to Cu sub-monolayer coverages are reversible. Strong kinetic effects arise for higher Cu coverage during the deposition and dissolution, which gradually lower the reversibility of the electrocrystallization process. Dissolution of the full Cu monolayer is shifted positively by about 0.3 V. In addition, bulk deposition is kinetically hindered for an extended potential region. The acetate coverage on the complete Cu monolayer is estimated to be 0.2–0.3 ML. It is proposed that adsorbed acetate on the Cu UPD ML is related to the kinetic hindrance observed in the experiments. (Surface) alloying of Cu and Au is observed by cyclic voltammetry and in-situ STM.