The methanol oxidation reaction is a key reaction in the direct methanol fuel cells. Prior research indicates that, if oxygen vacancies in NiOOH serve as the active sites, the methanol oxidation mainly proceeds through the formate-involving pathway, which is a CO-free pathway, distinct from the conventional path over transition metal catalysts, though the fundamental reason of this suppressed CO formation is unclear. Here we report density functional theory calculations, through which we uncover the underlying reasons of this alternate path of methanol oxidation over the oxygen vacancies in NiOOH. We find that the existence of oxygen vacancies in NiOOH affects the adsorption configuration of adsorbates, and that the interfacial charge transfer is minimal for CHO and CO intermediates. In addition, CHO, a key intermediate to form CO, adsorbs at the oxygen vacancy through the oxygen atom, leading to low stability due to the incomplete valence saturation of the carbon atom. This weak electronic interaction and instability effectively inhibits the CHO formation and consequently CO formation. These insights provide important guidance for the development of efficient and CO-tolerant catalysts for methanol oxidation.
