Adsorption of CO poison on fuel cell nanoparticle electrodes from methanol solutions: a radioactive labeling study

Combined radioactive labeling and electrochemical measurements were conducted to study adsorption and desorption of methanol-derived surface CO on fuel-cell grade platinum and platinum–ruthenium alloy nanoparticle catalysts. The adsorption results were obtained under constant potential and voltammetric conditions, and the experiments were carried out in sulfuric acid solutions containing methanol (at room temperature). The electrode potential effect on the CO coverage, the rates of methanol adsorption and CO desorption, as well as the susceptibility of the CO adsorbate to exchange with bulk methanol (surface/bulk exchange) were investigated. We found that CO adsorption at low electrode potentials was slower than at higher potentials, but higher coverages were obtained at the low potentials. Adsorption, desorption and surface/bulk exchange processes were significantly different on Pt than on Pt/Ru, confirming some of the previous results published in the electrochemical literature. The higher rate of methanol adsorption on Pt/Ru is explained on the basis of electronic modification of platinum by ruthenium using state-of-the-art concepts from the theory of electrocatalytic reactivity. We also report that combined bifunctional and ligand effects account for the difference in desorption kinetics. Finally, the relevance of our observations to the processes occurring on the anode of the direct methanol oxidation fuel cell is highlighted.