On the Behavior of Pt(111)−Bi in Acid and Alkaline Electrolytes

We studied the base voltammetry of Pt(111) modified by irreversibly adsorbed Bi in both 0.1 M HClO<INF>4</INF> and 0.1 M NaOH. By comparing the cyclic voltammograms in both electrolytes for the same Bi<INF>ir</INF> coverages, we found the following. (i) For highly Bi<INF>ir</INF> covered surfaces, significantly higher H<INF>upd</INF> coverages are found in alkaline solution, indicating that the H<INF>upd</INF> charge cannot be unambiguously correlated to the Bi<INF>ir</INF> coverage. (ii) In line with our previous model of enhanced adsorption of OH<INF>ad</INF> on Pt sites adjacent to Bi<INF>ir</INF>, we also propose the enhanced formation of surface oxide layers on Pt(111)−Bi<INF>ir</INF> electrodes. CO stripping experiments on surfaces with different Bi<INF>ir</INF> surface coverages in perchloric acid showed that on a highly Bi covered Pt(111) surface the CO oxidation starts at higher potentials than on a surface with lower Bi coverage. This finding implies that in the Langmuir−Hinshelwood surface reaction for CO oxidation both reaction partners compete for the same adsorption sites, that is, Pt(111)−Bi<INF>ir</INF> does not represent a bifunctional surface.