ADSORPTION OF ANIONS ON ULTRATHIN METAL DEPOSITS ON SINGLE-CRYSTAL ELECTRODES .3. VOLTAMMETRIC AND RADIOCHEMICAL STUDY OF BISULFATE ADSORPTION ON PT(111) AND PT(POLY) ELECTRODES CONTAINING SILVER ADATOMS

Radiochemical and electrochemical results for the adsorption of bisulfate on underpotentially deposited silver on Pt(111) are presented. In the extreme negative and positive electrode potential ranges investigated, silver is deposited as a clean metal phase or silver oxide phase, respectively. The latter phase is most probably intermixed with clean silver and platinum oxides. When the charge needed for surface oxidation is accounted for, the net charge in the underpotential deposition range corresponds to two monolayers of silver. Enhanced adsorption of bisulfate on the thin silver deposits attains a saturation coverage at 10(-5) M sulfuric acid in 0.1 M perchloric acid. Despite the strong adsorption, bisulfate anions rapidly exchange with bulk anions, which attests to a dynamic character of adsorption. The rate of surface to bulk bisulfate exchange on silver deposited on platinum does not differ (on the time-scale of our method) from that on a solid silver electrode, which allows us to conclude that the surface properties of these two different silver substrates are similar. Bisulfate adsorption on platinum-stabilized silver oxide is weaker than on the clean silver deposit. Complementary data on bisulfate adsorption on clean Pt(111), Pt(poly) and solid silver electrodes are also presented and discussed.