Underpotential deposition of zinc ions at single crystal electrodes and the effect of the adsorbed anions

Underpotential deposition (upd) of Zn2+ ions on Pt(111) and Au(111) is focu ssed in view of anion adsorption/desorption process, since Zn upd processes receive various effects of anions during the course of the processes, of w hich characteristics are different between Au and Pt. The difference is cle arly demonstrated, being discussed by means of work function, point of zero charge (pzc) and the presence/absence of preadsorbed anion in the region o f upd. The coincidence of kinetics of preadsorbed anion and upd Zn for the case of Pt(111) in phosphate solution at pH 4.6 is discussed by random adso rption/desorption of the Langmuir type. In the case of Zn upd on Au(111) in the same solution, two dimensional phase formation/desorption by nucleatio n-growth type was concluded, where the preadsorbed anion is not present at onset potential of Zn upd, and therefore the facilitation by the adsorbed a nion is not present. However, we can expect that the position of pzc is loc ated at more positive potential than the upd onset potential; the electrost atic interaction toward Zn2+ is an attractive force to the electrode, which is discussed to assist in nucleation-growth mechanism for two-dimensional upd phase formation by lateral interaction. We have tried to understand the upd phenomenon in general by means of the Zn upd process. (C) 1998 Elsevie r Science Ltd. All rights reserved.