Dynamic electrochemical impedance study of methanol oxidation at Pt at elevated temperatures

The methanol oxidation reaction (MOR) is studied at temperatures up to 140 degrees C by a combination of cyclic voltammetry, chronoamperometry, and dynamic electrochemical impedance spectroscopy (dEIS). A mechanistic analysis of the reaction is done based on the Tafel relation, the calculated activation energy, and the fitting of dEIS data. At the fuel cell relevant potentials, 0-0.80 V vs RHE, the MOR mechanism is similar at all temperatures. The rate-determining step is the adsorption of water at low overpotentials (< 0.50 V vs RHE), a combination of the methanol adsorption reaction and the surface reaction between adsorbed CO and OH at intermediate potentials (0.50-0.65 V vs RHE), and the methanol adsorption reaction at high potentials (> 0.65 V vs RHE). The shoulder on the oxidation peak at 0.60-0.65 V vs RHE corresponds well with where the CO coverage approaches zero. (C) 2018 Elsevier Ltd. All rights reserved.