Potential dependence of the saturation CO coverage of Pt electrodes:: The origin of the pre-peak in CO-stripping voltammograms.: Part 3:: Pt(poly)

We have determined the maximum CO coverage attained at polycrystalline Pt electrodes in CO-free sulphuric acid solutions, using both CO-stripping cyclic voltammetry and the integrated intensity of the infrared absorption band Of CO2 formed upon oxidation of the adsorbed CO, as a function of the dosing potential (E-d). Our results are similar to those previously reported for CO adsorbed on Pt(111) and Pt(100) electrodes, and show a decrease of the CO coverage with increasing Ed, a pre-peak between 0.35 and 0.65 V vs. RHE in the CO-stripping voltammograms appearing only for the high-coverage CO adlayers formed at E-d < 0.30-0.35 V. FT-IRS was also used to monitor the changes occurring in the CO adlayer as a consequence of minute variations in the CO coverage, and to confirm our previous results on the effect of chloride ions on the electrooxidation of adsorbed CO. The CO coverage was found to be independent of the chloride concentration in the solution, and at E < 0.7 V chloride has a negligible effect on CO stripping, competition between Cl- and OH for the available adsorption sites being relevant only at E >= 0.7 V, when a significant fraction of the CO adlayer has been oxidised. (c) 2005 Elsevier B.V. All rights reserved.