We studied the base voltammetry of Pt(111) modified by irreversibly adsorbed Bi in both 0.1 M HClO4 and 0.1 M NaOH. By comparing the cyclic voltammograms in both electrolytes for the same Bi-ir coverages, we found the following. (i) For highly Bi-ir covered surfaces, significantly higher ll pd coverages are found in alkaline solution, indicating that the H-upd charge cannot be unambiguously correlated to the Bi-ir coverage. (ii) In line with our previous model of enhanced adsorption of OHad on Pt sites adjacent to Bi-ir, we also propose the enhanced formation of surface oxide layers on Pt(111)-Bi-ir electrodes. CO stripping experiments on surfaces with different Bi-ir 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-ir does not represent a bifunctional surface.