Unraveling the impact of temperature on the reaction kinetics of the electro-oxidation of methanol on Pt(1 0 0)

Abstract

Methanol is one of the key molecules in the challenge towards a sustainable future, particularly as a renewable hydrogen carrier fuel and as a low-carbon and net carbon-neutral liquid chemical. For most applications, it is imperative to understand the impact of temperature on the methanol electro-oxidation reaction (MEOR). In this study, the influence of the temperature on the kinetics of the MEOR and the parallel reaction pathways is assessed by investigating responses in both conventional and oscillatory regimes using a single-crystal Pt(100) electrode. Our findings demonstrate that chronoamperometric measurements under steady-state conditions provide more reliable values for apparent activation energies compared to transient conditions. Furthermore, a temperature-dependent shift in the dominance of specific oxidation pathways is observed, analogous to a kinetic and thermodynamic control mechanism, preventing the complete poisoning of the electrode surface. Specifically, oxidation pathways leading to the formation of reaction byproducts predominate at lower temperatures, while the oxidation pathway via COad becomes dominant at temperatures exceeding 30 °C. Moreover, our research shows that, at shorter times, temperature changes minimally affect the mean potential required to sustain the applied current during the oscillations in a galvanostatic experiment, which is closely linked with the voltaic efficiency. However, over longer periods, when mass transport phenomena become significant and mixed-mode oscillations occur, elevated temperatures increase the mean potential, resulting in reduced voltaic efficiency. Therefore, to facilitate the complete conversion of methanol to CO2 without increasing the mean potential for current maintenance, it is essential not only to increase the temperature but also to improve the mass transport conditions to mitigate the mixed-mode oscillations, despite their lower minima reached during oscillation. This idea challenges the conventional assumption that a lower minimum potential implies a lower mean potential during oscillations. This advancement propels our understanding to a more sophisticated level, providing valuable insights to guide the materials design to increase the conversion efficiency and optimize the operating temperature of devices crucial to energy conversion.