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.