Adsorption phenomena on polycrystalline gold electrode modified by Zn adatoms

In this paper, experimental results obtained by the in-situ radiotracer and voltammetric studies of the competitive adsorption of the HSO4-/SO42- (labeled with 35S) and Cl- (labeled with 36Cl) anions on bare Aupoly substrate and Aupoly surfaces modified by the Zn adatoms in the lower pH region (pH≤5) are presented and discussed. In addition, some data on the formation of Zn adlayers (labeled with 65Zn) are reported to demonstrate the complex features of the underpotential deposition (UPD) phenomenon. It has been revealed that (1) the relative adsorption strength of Cl- ions on bare Aupoly is higher than that of H2PO4-/PO43- and HSO4-/SO42- ions in the entire pH region studied; (2) anomalous tendency of the specific adsorption of anions on polycrystalline gold modified by Zn adatoms occurs at pH 4.5 as follows: PO43- > SO42- > Cl- >>ClO4- and (3) the UPD of Zn2+ ions on polycrystalline gold is measurable even from solutions containing 5 X 10-8M Zn2+ over the entire potential range where the hydrogen evolution takes place. It is, however, plausible to assume that the coverage of the gold surface by Zn adatoms measured even at solution concentrations of c ≥10-4M does not exceed one monolayer. (author)