THE ELUCIDATION OF HYDROGEN AND ANION ADSORPTION ON PT(111) THROUGH THE COADSORPTION OF METAL ADATOMS AND CARBON-MONOXIDE

Copper, lead and carbon monoxide adsorbates have been used to probe the adsorption processes on a Pt(111) electrode in H2SO4 and HClO4 solutions. All three adsorbates cause inhibition of hydrogen adsorption in both solutions and a decrease of the anomalous peak recently ascribed to HSO4- adsorption. The "butterfly" peak in HClO4 solution is slightly perturbed by Cu and Pb adatoms. Evidence was found that the species responsible for the anomalous peak for Pt(111) in H2SO4 solutions is not H(ads) and that HSO4- probably interacts with three Pt(111) sites. A twofold interaction of HSO4-with the Pt(111) surface, however, cannot be ruled out completely. In HClO4 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 HSO4-ads 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.