UNDERPOTENTIAL DEPOSITION OF COPPER AND ITS INFLUENCE IN THE OXYGEN REDUCTION ON PLATINUM

The underpotential deposition (UPD) of Cu on Pt was studied in acid media using cyclic voltammetry and rotating ring-disk electrode techniques. Experimental data at sub-monolayer levels demonstrate that ad-atom formation occurs in different energy states and no rearrangements take place in the ad-layer. Rotating ring-disk studies of the oxygen reduction reaction on Cu UPD show a strong inhibition of the reaction only in the region of diffusion control. At first, the 4e reaction to H2O is inhibited in favor of the 2e reaction to H2O2 but at more negative potentials even the formation of H2O2 is inhibited. A mechanism based on the degree of surface-active sites blocked by Cu ad-atoms is proposed.