VOLTAMMETRIC STUDY OF THE ELECTROADSORPTION AND ELECTROOXIDATION OF CO ON PT IN 0.5 M HCLO4 - INFLUENCE OF SEVERAL EXPERIMENTAL-VARIABLES

The influence of several variables on the voltammogram at 20 mV s - 1 of Pt in 0.5 M HClO4 with different CO concentrations and using a flow cell has been studied. Up to four anodic peaks can appear simultaneously in the voltammogram: the first peak, at 0.50-0.72 V vs. a reversible hydrogen electrode, is due to the electrooxidation of dissolved CO; according to reported IR spectra, peak II, at 0.71-0.82 V, and peak III, at 0.89-0.95 V, both correspond to the electrooxidation of linearly adsorbed CO; peak IV, at 0.95-1.02 V, is probably due to the formation of a Pt oxide. The definition of the peaks increased with the degree of polishing of the Pt electrode, and consequently a final polish with 0.05 mum alumina was used. A procedure was found with which the evolution of the different peaks took tens of minutes, which allowed us to establish that the presence of peak III was a necessary, but not sufficient, condition for peak IV to be observed. The other conditions that led to a large peak IV were determined. It was also found that both a decreasing concentration of CO in solution and an increasing dilution of a CO-saturated solution with which the Pt electrode had been previously in contact for 5 min produced an increase of peak II at the expense of peak III, which would support the contention that peak III corresponds to the electrooxidation of a physisorbed CO species. However, this is in direct contradiction with the above-mentioned IR results, according to which both surface CO species giving rise to peaks II and III are linearly chemisorbed CO.