The elucidation of hydrogen and anion adsorption on Pt(111) through the co-adsorption of metal adatoms and carbon monoxide

Abstract Copper, lead and carbon monoxide adsorbates have been used to probe the adsorption processes on a Pt(111) electrode in H 2 SO 4 and HClO 4 solutions. All three adsorbates cause inhibition of hydrogen adsorption in both solutions and a decrease of the anomalous peak recently ascribed to HSO 4 − adsorption. The “butterfly” peak in HClO 4 solution is slightly perturbed by Cu and Pb adatoms. Evidence was found that the species responsible for the anomalous peak for Pt(111) in H 2 SO 4 solutions is not H ads and that HSO 4 − probably interacts with three Pt(111) sites. A twofold interaction of HSO 4 − with the Pt(111) surface, however, cannot be ruled out completely. In HClO 4 solutions the Cu and Pb adatoms do not cause any decrease of the charge associated with the “butterfly” peak. These results can be explained in terms of PtOH as the species involved with the “butterfly” peak. The electrosorption valence of HSO 4ads − is unity, which indicates a strong interaction with the surface and a high charge transfer. The Temkin interaction parameter for H ads is fRT = 42 kJ mol −1 , which provides evidence for a large repulsive interaction of H ads on the Pt(111) surface. It decreases in the presence of Cu and CO adsorbates. These results illustrate the usefulness of the competitive adsorption of various adsorbates in probing adsorption processes on electrode surfaces.