Combined Ultrahigh Vacuum/Electrochemistry Study of the Adsorption of Lead on Clean and Sulfur-Modified Nickel Surfaces in Aqueous Environments

The adsorption of lead on clean and sulfur-modified nickel surfaces was studied as a function of immersion time. The effect of preadsorbed sulfur and lead adsorption on nickel oxidation was also examined by open-circuit potential (OCP) measurements. Sulfur adsorbed on nickel inhibits the formation of the inner NiO layer, which results in an enhanced nickel oxidation/dissolution in aqueous solutions. The adsorption of lead is enhanced by as much as 1200% when the nickel electrode is first modified by a monolayer of adsorbed sulfur. The chemical shift in Pb(4f) binding energies indicates that lead (Pb 2+ ) ions interact directly with the preadsorbed sulfur on nickel. Lead adsorbed on sulfur-modified nickel electrode is also found to retard the oxidation/dissolution of nickel, which is enhanced by sulfur. On sulfur-modified nickel surfaces, 70% of the lead adsorption occurs during the initial 30 s of immersion. The rate of lead adsorption approaches zero after an immersion time of 10 min. On the basis of the observations of this study, a model for the sulfur-induced lead adsorption has been formulated.