EFFECTS OF ADSORBED CO ON HYDROGEN IONIZATION AND CO OXIDATION REACTIONS AT PT SINGLE-CRYSTAL ELECTRODES IN ACIDIC SOLUTION

CO was adsorbed on the three low index planes of Pt single-crystal ele ctrodes, and the hydrogen ionization and the dissolved CO oxidation re actions on the GO-covered electrodes were investigated in acid solutio n. The oxidation wave of CO adsorbed at 50 mV vs. a reversible hydroge n electrode had two peaks; a small prepeak at around 0.5 V and a main oxidation peak at around 0.7 V. Fourier transform IR measurement and t he number of electrons per site for adsorbed CO indicated that these o xidation peaks could not be assigned individually to the linear and th e bridged CO species. These peaks reflect the difference in the kineti c stability among the adsorbed CO. The stripping of the prepeak CO (CO I(a)) initiated both the hydrogen ionization and the dissolved CO oxid ation reactions to a value close to the diffusion-limited values. Thes e reactions required only a very small number of free sites which are provided in the present case by the removal of the kinetically unstabl e COI(a). COI(a) was absent in the adsorbed CO at 0.4 V. The voltammog rams for the dissolved CO oxidation on the CO-covered electrodes revea led the presence of other two adsorbed states, COII(a) and COIII(a), w here COII(a) was most stable and gave the main peak of the oxidation w ave of the adsorbed CO. COIII(a) was very sensitive to the experimenta l conditions and was responsible for the hump that appeared in the dis solved CO oxidation.