Surface and Subsurface Oxygen on Platinum in a Copper Perchlorate Solution

Abstract

The formation of an adatom layer on polycrystalline platinum and the three-dimensional nucleation of copper in a 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 E a 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 (Oss), which appears on the platinum surface after the destruction of complexes Oss–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.