Dependence on the CO admission potential of the activation energy of the electrooxidation of adsorbed CO on Pt

We have obtained the activation energy for the electrooxidation of adsorbed CO on a Pt wire as the intercept of the plot of the peak potential (vs. the standard hydrogen electrode at 298 K) of adsorbed CO electrooxidation in CO-stripping voltammograms vs. the absolute temperature. The activation energy for the electrooxidation of CO adsorbed on a Pt wire in CO-saturated 0.1 M HClO4 was 1.28 and 2.17 V for CO admission potentials (the potential at which the electrode is held while CO is first introduced in the cell) of 0.03 and 0.35 V, respectively, this increase of 70% clearly showing that the CO adlayer formed at 0.35 V resists oxidation much better than that formed at 0.03 V, although its CO coverage is smaller. This apparent contradiction is explained by the appearance of a pre-peak in the CO stripping CV only when the CO admission potential is lower than 0.3 V, since OH groups can nucleate on the sites left free by the electrooxidation of some CO in the pre-peak, thereby facilitating the electrooxidation of the remaining adsorbed CO. For admission potentials in the range 0.03-0.10 V, the activation energy found here for Pt wire was 9% lower than that reported for Pt(1 1 1) and for admission potentials in the range 0.30-0.35 V the activation energy found here for Pt wire was 22% higher than that calculated from reported CVs for carbon-supported Pt nanoparticles. Both at low and high admission potentials, the activation energy calculated from reported CVs for the electrooxidation of CO adsorbed on Pt electrodeposited on glassy carbon was about 24% higher than that for Pt wire. So, we have been able to quantify the electrocatalytic activity of different forms of Pt.