Influence of organic adsorbates on the under and overpotential deposition of copper on polycrystalline platinum electrodes

The deposition of copper onto a polycrystalline platinum surface has been studied in the underpotential (upd) and overpotential (opd) regions using cyclic voltammetry in the presence of organic co-adsorbates including pyridine, pyrazine, 2,2'-bipyridine, 4,4'-bipyridine, 4-phenylpyridine, 1,2-bis(4-pyridyl)ethane, 2-mercaptopyridine and 4-mercaptopyridine dissolved in either 0.5 M H2SO4 or water. Adsorbates that bind primarily through a ring nitrogen atom delay both the upd and opd processes, depending on the bond strength of the adsorbed layer. These adsorbates also show a significant pH dependence due to protonation of the binding nitrogen atom. On the other hand, the sulfur containing adsorbates completely inhibit the underpotential deposition but not the overpotential deposition process. In addition, a monolayer of copper electrodeposited onto a platinum surface is oxidized upon exposure of the electrode to a solution of 2-mercaptopyridine which is, in turn, reduced. (C) 1997 Elsevier Science Ltd.