Microkinetic Modeling of the Methanol Electro-oxidation Reaction on Platinum

The development of electrocatalysts with high activity at low overpotentials for methanol electro-oxidation reaction is one of the challenges to overcome towards the wider applicability of this alcohol in energy conversion systems. Many works in the last decades have contributed with mechanistic studies on this reaction. Nevertheless, the reaction scheme is entangled which makes difficult to correlate it with the kinetic response in electrochemical experiments. In this paper we propose a microkinetic model for the methanol electro-oxidation reaction on polycrystalline platinum. The model was built on relevant mechanistic aspects available in the literature and formulated based on the mean-field approach. The kinetic parameters were determined by optimization and the validation was performed through the comparison with distinct sets of experimental data, namely cyclic voltammetry, chronoamperometry, and also oscillatory time-series recorded under galvanostatic conditions. The resulting model was able to simulate successfully the nonlinear dynamics observed in galvanostatic experiments, including chaotic behavior, as well as a reasonable voltammetric profile with the same set of electrokinetic parameters. The sensitivity analysis of the kinetic parameters showed that the electro-oxidation pathway through the formic acid intermediate is not significant under these experimental conditions and that the OHad and COad species are mainly involved in the origin of the oscillations, while species that affect the rate of formation/consumption of the latter causes the mixed-mode oscillations. The electrokinetic parameters were discussed with the data available for the electrooxidation reaction of formic acid, where the connection between the values highlights the applicability of this approach to other electrocatalytic reactions.