X-ray scattering studies of irreversibly adsorbed bismuth on the Pt(111) electrode surface

The surface electrochemistry of irreversibly adsorbed bismuth (Bi-ir) on th e Pt(111) electrode in 0.1 M HClO4 has been studied by in situ surface X-ra y scattering to correlate the atomic structure with the voltammetric featur es. Bi-ir saturates at a coverage of similar to one-third of a monolayer an d forms a disordered structure on the Pt(111) surface with some evidence th at the Bi-ir is mobile. If the Bi-ir coverage is slightly increased, then t here is a reduction in the charge under the reversible peaks in the cyclic voltammetry at a potential of similar to0.68 V (vs Pd/H-2). The charge unde r the reversible peaks is most likely associated with the adsorption of oxy genated species at platinum sites adjacent to Bi-ir atoms. Saturation of th e electrolyte with CO and subsequent potential cycling leads to displacemen t of Bi-ir from the surface and the appearance of an X-ray diffraction patt ern due to a p(2 x 2)-3CO adlayer that has previously been observed on the unmodified Pt(111) electrode.