Surface and subsurface oxygen on platinum in a copper perchlorate solution

The formation of an adatom layer on polycrystalline platinum and the three-dimensional nucleation of copper in copper perchlorate solution are studied by cyclic voltammetry at 0.1 V s(-1) while varying potential ranges and by recording potentiostatic current transients. About 0.6 monolayers of copper adatoms are deposited when cycling with anodic limit E-a = 1.35 V, the process is slower than that in an acid sulfate solution. Decreasing Ea accelerates the process (nearly one monolayer forms for E-a = 0.80-0.95 V in a cathodic scan) due to an increased number of active centers (metastable copper oxides) and, probably, to a change in the platinum surface microstructure. Oxygen for copper oxides is presumably supplied by water molecules adsorbed on a monolayer of copper adsorbed atoms and by subsurface oxygen (O-ss), which appears on the platinum surface after the destruction of complexes O-ss-Pt-n-ClO4. Both the copper nucleation and the deposit growth accelerate at higher concentrations of copper oxides, which form at low E-a. High cathodic overvoltages decrease the number of active crystallization centers due to reduction or removal of copper oxides.