Influence of organic adsorbates on the under- and overpotential deposition of copper on gold electrodes

The electrodeposition of copper onto polycrystalline gold electrodes has been studied in the under- (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-pyridil)ethylene, 2-mercaptopyridine and 4-mercaptopyridine dissolved in either 0.5 M H2SO4 or water. Adsorbates binding primarily through a ring nitrogen atom delay the upd process and change the distribution of charge of both the deposition/stripping of copper. Of the two, sulfur containing adsorbates, 2-mercaptopyridine inhibits both the under- and overpotential deposition, due to the formation of a surface chelate. On the other hand, 4-mercaptopyridine only inhibits the upd process when it is adsorbed at constant potential.