Resolution of the mechanism of CO electrooxidation on steady state and evaluation of the kinetic parameters for Pt and Ru electrodes

Abstract

The carbon monoxide oxidation reaction (COOR) was studied on steady-state conditions by chronoamperometry on polycrystalline smooth platinum and ruthenium rotating disc electrodes in CO-saturated acid solution. The chronoamperometric response did not show current oscillations and therefore the current density (j) vs. overpotential (η) curves on steady state could be obtained. In order to interpret these results, kinetic expressions were derived starting from the mechanism proposed by S. Gilman, which considers two adsorbed reaction intermediates, carbonmonoxide (CO ad) and hydroxyl (OH ad). Analytical expressions as a function of overpotential for the current density, the surface coverage of the adsorbed species (θ CO and θ OH) and the CO and CO 2 pressures at the electrode surface on steady state were obtained. This set of equations was used for the correlation of the experimental polarization curves and the evaluation of the corresponding kinetic parameters. From these values, the dependences of the surface coverage of the adsorbed intermediates on overpotential were simulated, as well as those of the partial pressure of CO and CO 2. Thus, it was demonstrated that the Gilman's mechanism accurately describes the experimental results on steady state of the COOR on these metals.