Combined ultrahigh vacuum electrochemistry studies of copper and sulfur-modified copper electrodes in mildly acidic phosphate electrolyte

The effect of similar to0.1 monolayer of adsorbed S on the electrochemical response of polycrystalline Cu in a phosphate buffer electrolyte at pH 6.4 has been studied using combined ultrahigh vacuum electrochemistry methodolo gy. This study shows that the anodic dissolution current is higher for both S-free Cu and S-modified Cu electrodes at pH 6.4, when compared to dissolu tion currents observed in a previous study in a borate buffer at pH 8.4. Th e absence of CuO in the surface oxide-hydroxide layer for electrodes subjec ted to anodic dissolution in the phosphate buffer is proposed to be the mai n reason for enhanced dissolution currents observed at this pH. The presenc e of adsorbed S does not have a significant effect on anodic dissolution co ntrary to the behavior observed in the previous study in borate buffer. Ads orbed S is found to inhibit oxide-hydroxide formation at the peak dissoluti on potential. (C) 2001 The Electrochemical Society.