Overpotential deposition of copper on an iodine-modified Au(1 1 1) electrode

Cyclic voltammetry, chronoamperometry and in situ electrochemical scanning tunneling microscopy were used to study the kinetics of nucleation and crystal growth during the initial stages of copper overpotential deposition (OPD) on a previously iodine-modified Au(1 1 1) electrode, from an aqueous solution 10⁻³ M CuSO₄ in 0.05 M H₂SO₄. The starting potential during step experiments was chosen in the region where the gold electrode was completely free of the copper deposit. The recorded current transients for copper deposition onto the iodine-modified Au(1 1 1) electrode surface appear to be very complex, with the unusual presence of two or more current maxima. A new method was used for quantitative evaluation of current transients that involves the transition UPD-OPD, developed by our group [M. Palomar-Pardavé, I. González, N. Batina, J. Phys. Chem. B 104 (2000) 3545], was used for the quantitative interpretation. Our results show that, within a single current transient, copper adsorption and two types of nucleation process: two-dimensional (2D) and three-dimensional (3D) limited by lattice incorporation of copper adatoms and diffusion of Cu(II) ion, respectively, take place simultaneously. STM images revealed the enhanced growth of 3D copper on edge of I-Au(1 1 1) during the early stages of deposition. Moreover, our results strongly suggest that the iodine adlayer is constantly present, even after the striping Cu that was overpotential deposited.