The Chameleon Role of Interfacial Hydroxyls: Reaction-Condition-Dependent Dynamics in Methanol Electro-Oxidation

The electrocatalytic oxidation of methanol on platinum represents a model system for alcohol fuel-cell chemistry, yet the precise role of interfacial hydroxyl (OH*), a key oxidative species, remains contentious and is often viewed simplistically as either a co-reactant or a poison. Herein, ab initio molecular dynamics simulations with explicit solvation were employed to transcend this binary perspective, revealing OH* as a dynamic interfacial mediator whose coverage influences methanol activation and mechanistic pathways. Under oxidative potentials, increasing OH* coverage leads to the formation of an interfacial adsorbate layer interconnected by hydrogen bonds. Frequent proton transfer within this layer facilitates spontaneous O–H bond cleavage of methanol, while fluctuations in the hydrogen-bond network further promote its pre-oxidation and activation. In contrast, OH*-mediated C–H oxidation involves a high free-energy barrier, and increasing OH* coverage reduces the availability of Pt sites required for C–H dissociation, potentially contributing to surface poisoning. Importantly, site competition induced by high OH* coverage also alters the configuration of the reaction-generated HCHO intermediate, reducing the accessibility of further C–H cleavage toward CO* while enabling direct reaction with OH* toward formate through a CO*-free pathway. Together, these results reveal a coverage-dependent trade-off among O–H activation, the availability of Pt sites for C–H bond cleavage, and subsequent pathway selection. Regulating interfacial OH* coverage therefore provides a possible means to tune methanol oxidation activity and pathway selectivity.