Cyclic voltammetry and XPS studies of monolayers deposited on gold and platinum electrodes displaced by mercaptopyridines.

We present studies, by cyclic voltammetry and X-ray photoelectron spectroscopy (XPS), of the under and overpotential deposition of copper on polycrystalline platinum and gold electrodes in aqueous 0.50 M sulfuric acid solution in the presence and absence of adsorbed layers of 2- and 4-mercaptopyridine (2-MP, 4-MP). In general we find that the presence of adsorbed layers of either 2-MP or 4-MP gives rise to an inhibition of the electrodeposition processes consistent with very strong interaction of the adsorbates with both Pt and Au surfaces. 2-MP gave rise to a higher degree of inhibition which we ascribe to a stronger degree of interaction likely due to a formation of a surface chelate via bonding through both N and S atoms. We have also investigated the reaction of 2-MP and 4-MP in solution with polycrystalline platinum and gold electrodes in aqueous 0.50 M sulfuric acid solution and which were either bare or covered by electrodeposited oxide or copper monolayers. Our studies reveal that the electrodeposited copper monolayer is displaced (oxidized), partially or completely, depending on the electrode material (Pt vs. Au),by 2-MP and 4-MP. On the other hand, the platinum and gold oxide monolayers are completely displaced by both adsorbates. The reactions of the oxide and copper monolayers with 2-MP and 4-MP gave rise to adsorbed intermediates and we present possible mechanistic pathways for these processes. (C) 1997 Elsevier Science S.A.