The Importance of the Electrochemical Environment in the Electro-Oxidation of Methanol on Pt(111)

The electro-oxidation of methanol on Pt(111) is studied based on periodic density functional theory calculations. The aqueous electrolyte is taken into account using an implicit solvent model, and the dependence of the reaction energetics on the electrode potential is derived using the concept of the computational hydrogen electrode. The total oxidation of methanol becomes thermodynamically preferred at electrode potentials above U = 0.6 V relative to the standard hydrogen electrode. We propose a most favorable reaction path involving surface carboxyl as the last reaction intermediate before CO2 formation, which can either be formed in a indirect mechanism from adsorbed CO or in a direct mechanism from formic acid. The presence of the aqueous electrolyte significantly stabilizes reaction intermediates that contain hydrophilic groups. This also leads to a selectivity for the initial C-H bond breaking process with respect to the initial O-H bond breaking of methanol that is increased by 3 orders of magnitude at room temperature when solvent effects are considered.