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

We present studies, by cyclic voltannnetry and X-ray photoelectron specu'oscopy (XPS), of the under and oveq~otenfial deposition of copper on polycrystalline platinum and gold electrodes in aqueous 0.50 M sulfuric acid solution in the presence and absence of ads(~r~d layers of 2and 4-mereaptopyridine (2-MP, 4°MP). in general we find that the presence of adsorbed htyers of either 2-MP {~r 4-MP gives rise to an iBhihition of the electrodeposilion processes consistent with very sttx~ng interaction of the adsorbates with both Pt and Au surfaces. 2oMP gave rise to a higher degree of inhibition which we ascribe to a stronger degree of interaction likely due to a formation of a nurl~ce chel,'ae via honding through bolh N and S atoms. We have also investigated the reaction of 2-MP and 4-MP in solution wilh polycryslalline 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 thai 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 h:md. tile platinum and gold oxide monolayers are completely displaced by both adsorbates. The reactions of the oxide and copper monolayers with 2oMP and 4oMP gave rise to adsorbed intermediates and we present p~ssible mechanistic pathways lot these processes. ~) 1997 Elsevier Science S.A. Key.,ord.~: t.'opper; (Jold: PlatinunK Xoray I~ht~1o¢1¢¢11'Oll npeclm't~,,copy (XPS); Cyclic wdlal|lm¢lry