Oxygen Migration Pathways in the Methanol Oxidation Reaction

Methanol is a promising hydrogen carrier and clean fuel, particularly when synthesized from green hydrogen and captured CO2. Its oxidation reaction is a key half-cell process in both electrochemical reforming for hydrogen and direct methanol fuel cells (DMFCs). Traditionally, methanol oxidation on Pt catalysts is understood to proceed via dual pathways: an indirect route involving *CO intermediates and a direct route producing soluble species such as formaldehyde and formate. However, our 18O isotope labeling experiments with H218O and CH318OH have, for the first time, revealed that a majority proportion of methanol-derived oxygen does not appear in the final products, especially under alkaline conditions. To resolve this discrepancy, we propose a revolutionized pathway featuring the *O*OCHOH intermediate and the C–O bond dissociation of methanol. This mechanism, supported by control experiments and density functional theory (DFT) calculations, coexists with the conventional indirect pathway and explains the observed high C–O bond cleavage ratios (~65% in acid and >75% in base). Moreover, mechanistic studies show that increasing hydroxide concentration enhances the oxidation state of Pt, modulating the reaction pathway and affecting the Faradaic efficiencies of CO2/CO32− and HCOOH /HCOO− products. These findings provide a fundamental understanding of methanol oxidation, emphasize the crucial role of surface oxygen coverage and pH, and strengthen methanol’s potential as a sustainable fuel and hydrogen carrier for energy storage and DMFC technologies.