Bromide adsorption on Pt(100): Rotating ring Pt(100) disk electrode and surface X-ray scattering measurements

The rotating ring-disk electrode technique with a Pt(100) single crystal disk electrode is used to establish both the bromide adsorption isotherm and the electrosorption valency on Pt(100). In 0.1M HClO4 with similar to 10(-4)Br(-), bromide adsorption begins at about -0.25 V and reaches a coverage of similar to 0.42 ML at 0.5 V; the electrosorption valency is essentially unity. The major peak in the voltammetry at similar to-0.1 V is the simultaneous adsorption/desorption of hydrogen and desorption/adsorption of Br-. By subtracting the Br- flux we are able to deconvolute the charge for the hydrogen adsorption in the presence of Br-. The saturation coverage is about the same as in solution free of Br- similar to 210 mu C cm(-2), but the potential region for the onset of adsorption is shifted negatively by 0.35 V due to the competition with Br- adsorption. The reversible pseudocapacitive feature recorded in 0.1M HClO4 at 0.175 less than or similar to E less than or similar to 0.375 V should be assigned to the reversible adsorption of hydroxyl species. Despite the inability to detect any in-plane superlattice peaks corresponding to a long-range ordered structure in the Br adlayer, the x-ray scattering data provide information about the surface normal structure and local bonding sites for the Br adlayer on Pt(100).