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 bisulf ate on underpotentially deposited silver on Pt(111) are presented. In the extreme negative and positive electrode potential ranges investiga ted, 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 oxidat ion 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 a dsorption, bisulfate anions rapidly exchange with bulk anions, which a ttests to a dynamic character of adsorption. The rate of surface to bu lk bisulfate exchange on silver deposited on platinum does not differ (on the time-scale of our method) from that on a solid silver electrod e, which allows us to conclude that the surface properties of these tw o different silver substrates are similar. Bisulfate adsorption on pla tinum-stabilized silver oxide is weaker than on the clean silver depos it. Complementary data on bisulfate adsorption on clean Pt(111), Pt(po ly) and solid silver electrodes are also presented and discussed.