Investigations of SO42− adsorption at the Au(111) electrode in the presence of underpotentially deposited copper adatoms

Adsorption of Cl − at the Au(111) electrode in the presence of underpotentially deposited copper adatoms is described. It is shown that the underpotential deposition of copper promotes adsorption of Cl − , and at high or intermediate underpotentials a mixed overlayer which consists of copper adatoms and coadsorbed Cl − ions is formed. At intermediate underpotentials, the surface concentration of Cl − in the mixed overlayer amounts to 8 × 10 14 ions cm −2 which is only 10% less than the concentration of Cl − in the close-packed monolayer of Cl − . This surface concentration of Cl − is independent of the concentration of Cl − and Cu 2+ in the bulk. In solutions of low Cl − or Cu 2+ concentrations and at low underpotentials the surface concentration of Cl − decreases when the copper coverage approaches a monolayer. In solutions of high copper and chloride concentrations and low underpotentials the surface concentration of Cl − increases above the value of 8 × 10 14 ions cm −2 . The increase in the surface concentration of Cl − is observed when the copper coverage exceeds one monolayer. Therefore it may suggest formation of copper clusters or a trilayer.