Kinetics of copper deposition on Pt(111) and Au(111) electrodes in solutions of different acidities

Kinetics and mechanism of underpotential (UPD) and overpotential Cu deposition (OPD) on Pt(111), Pt(775) and Au(111) electrodes in sulfate solutions of different acidities (pH 0.3-3.7) are studied. In weakly acid solutions, the rates of both Cu UPD and OPD processes are higher as compared with acid solution of copper sulfate (pH 0.3) due to the enhanced concentration of active centers (copper oxides CuxO) for 2-D and 3-D phase transitions and accelerated discharge of copper ions. The maximum rate of (root 3 x root 3) R 30 degrees formation is observed at pH 2.7-3.0. At pH>3.0, the platinum surface is partially blocked by strongly adsorbed oxygen-containing species. At pH<2.7, the inhibition of Cu UPD and the adlayer desorption are due to the decrease in the charge transfer rate and concentration of copper oxides, which are the defects of adlayer. An optimal, not too high, concentration of adsorbed oxygen-containing species is necessary for ensuring the maximum rate of Cu UPD on platinum. Acidity of electrolytes affects considerably the rate of Cu deposition on Pt(111) but has only a slight influence on the kinetics of Cu UPD on Au(111) electrode due to the weaker adsorption of OH- ions on gold. However, the increase in pH accelerates bulk Cu deposition on Au(111). Adsorption of sulfate anions and hydroxide ions on a monolayer of copper adatoms and Cu crystallites provides accelerated charge transfer (local electrostatic double layer effects of electronegative species) and probably increases the amount of active centers for 3-D nucleation. (C) 2005 Elsevier Ltd. All rights reserved.