Mechanism for the Electro-oxidation of Carbon Monoxide on Platinum, Including Electrode Potential Dependence

B3LYP hybrid density functional calculations show that CO and OH bonded to Pt 2 react with a low activation energy (calculated 0.44 eV) to form -COOH bonded to a onefold site of Pt 2 . An OH bonded to the adjacent onefold site attracts the acid group by hydrogen bonding and a low activation energy (calculated 0.23 eV) separates this complex from CO 2 + H 2 O - Pt 2 . The similarity of the bond strengths between Pt 2 and CO, OH, and H 2 O to measured chemisorption bond strengths from the literature makes these results worth considering as a model for the electro-oxidation of CO(ads) by OH(ads) on platinum anodes. Calculations of activation energies for the oxidative deprotonation of Pt 2 - COOH indicate that high activation energies are to he expected for the reaction -COOH(ads) + H 2 O → CO 2 + H 3 O + (aq) + e (U) at the electrode potentials where CO(ads) is removed (∼0.6 V). Therefore, the formation of OH(ads) from oxidation of H 2 O, shown in another study to have a low activation energy and a reversible potential of ∼0.57 V, is concluded to be the cause of the observed overpotential for the electro-oxidation of CO(ads).