Underpotential deposition and metallic corrosion reaction

Abstract

Electrodeposition of metal ions, Mz, on foreign metal substrate, M', at potentials more positive than the reversible potential of the Mz/M electrode is termed "underpotential deposition (UPD)". The general feature of UPD was described, laying emphasis on the width of UPD potential window being to proportional to the difference in work function between two metals, M' and M. The effects of UPD on electrode reactions such as oxygen reduction, hydrogen evolution and metallic corrosion were reviewed and the discussion was made on the roles of UPD in the mechanism of electrode reactions. Particularly, the effect of Pb-UPD on corrosion of Ni was explained in detail with relation to the Pb-induced stress corrosion cracking (Pb-SCC) of Ni base alloys. Moreover, the structural change from UPD adsorption layer to surface alloy and the co-adsorption structure of electrolyte anions and of UPD metal atoms were exemplified and the importance of in-situ analysis of the electrode interface was pointed out to clarify the roles of UPD in reaction mechanism.