Direct Observation of Surface-Bound Intermediates During Methanol Oxidation on Platinum Under Alkaline Conditions

Direct methanol fuel cells (DMFCs) using alkaline electrolytes are of interest due to the applicability of nonprecious metal-based materials for electrocatalysts. However, the lack of understanding of the methanol oxidation reaction (MOR) mechanism in alkaline media hinders the development of active catalysts for the MOR In this work, ambient-pressure XPS and in situ surface-enhanced infrared spectroscopy were performed on the Pt surface in order to gain experimental insights into the reaction pathway for the MOR. We present a comprehensive reaction mechanism for the MOR in alkaline media and show that the MOR proceeds via two different pathways depending on the electrode potential. We confirmed the formation of partially hydrogenated CO adsorbates [HxCOad center dot center dot center dot(OH) (1 < x < 3)] via water and/or hydroxide ion-mediated dissociation of methanol. The HxCOad center dot center dot center dot(OH) species were further dehydrogenated to COad in the potential range of 0.40-0.60 V-RHE and subsequently oxidized to CO2 by reactive OHad on the Pt surface at 0.65 V-RHE (pathway I). Furthermore, H3C-O-ad intermediates were observed at potentials higher than 0.9 V-RHE, at which the MOR proceeds mainly via H3C-O-ad instead of COad intermediates (pathway II). The oxidation current related to this conversion from H3C-O-ad to CO2 (pathway II) dominates the overall MOR current, suggesting that the H3C-O-ad pathway could be one of the keys to enhancing the MOR activity in an alkaline environment. Our findings pave the way toward a design strategy for MOR electrocatalysts with improved activity based on the experimental reaction mechanisms that have been identified.

Automated summary

This study investigated the mechanism of methanol oxidation reaction in alkaline media through experimental methods and found that the reaction proceeds via two different pathways depending on the electrode potential, forming different intermediates. This provides insights into enhancing the activity of methanol oxidation reaction in alkaline environment.