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 cryst al disk electrode is used to establish both the bromide adsorption iso therm and the electrosorption valency on Pt(100). In 0.1M HClO4 with s imilar 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 si milar to-0.1 V is the simultaneous adsorption/desorption of hydrogen a nd desorption/adsorption of Br-. By subtracting the Br- flux we are ab le to deconvolute the charge for the hydrogen adsorption in the presen ce of Br-. The saturation coverage is about the same as in solution fr ee 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 compet ition with Br- adsorption. The reversible pseudocapacitive feature rec orded in 0.1M HClO4 at 0.175 less than or similar to E less than or si milar to 0.375 V should be assigned to the reversible adsorption of hy droxyl species. Despite the inability to detect any in-plane superlatt ice peaks corresponding to a long-range ordered structure in the Br ad layer, the x-ray scattering data provide information about the surface normal structure and local bonding sites for the Br adlayer on Pt(100 ).