Reconciling the experimental and computational methanol electro-oxidation activity via potential-dependent kinetic mechanism analysis

Abstract

The kinetic mechanism of the methanol oxidation reaction (MOR) has been controversial due to the lack of accurate monitoring technology and static calculation of the kinetic process, as well as the failure to consider the relationship between the free energy barriers and electrode potential. This work focused on Pt and PtRu catalysts and assessed the potential-dependent MOR kinetic process via metal–electrolyte models to reconcile the experimental and computational MOR activity. The obtained results demonstrate that the potential-dependent rate-determining steps (RDSs) change with the increase of electrode potential in the orders of (R3: CH₃O* → CH₂O* + H⁺ + e⁻) → (R5: CHO* → CO* + H⁺ + e⁻) → (R14: CO* + OH* → CO₂* + H⁺ + e⁻), and (R4: CH₂O* → CHO* + H⁺ + e⁻) → (R5: CHO* → CO* + H⁺ + e⁻) → (R14: CO* + OH* → CO₂* + H⁺ + e⁻), respectively, which is attributed to the variation in the adsorption of intermediates and strength of the electrochemical double layer (E_field). Furthermore, the potential-dependent coverage of intermediates and degree of rate control (DRC) in the MOR kinetic process draw support from microkinetic modeling. The experimental cyclic voltammograms and theoretical computation are reconciled with max absolute differences (Δ^max_abs) of 0.020 and 0.023 mA cm⁻² for Pt and PtRu, respectively, giving evidence for the nature of higher MOR activity for PtRu. Importantly, our explicitly dynamic approach elucidates the potential-dependent MOR kinetic process at both the molecular and atomic levels and paves the way for the complex multi-electron reaction kinetic simulation.