Temperature Effects on Methanol Dissociative Chemisorption and Water Activation at Polycrystalline Platinum Electrodes

Abstract

A thermostated IR spectroelectrochemical cell was used to probe the effects of temperature (25 − 70 °C) and methanol concentration (1.5 × 10-2 − 1.0 M) on methanol dissociative chemisorption at platinum electrodes in 0.1 M HClO4. The measurements provide molecular level evidence for mechanisms derived from electrochemical studies of methanol oxidation at above ambient temperatures. For fixed methanol concentrations, increasing the temperature lowered the quantity of detectable adsorbed CO and increased the rate of CO2 formation. The results can be understood in terms of the thermal activation of water and CO desorption. At fixed temperature, raising the methanol concentration in solution increased the integrated intensities of the adsorbed CO vibrational bands between 0.2 and 0.7 V (versus reversible hydrogen electrode, RHE). Below 0.9 V, the rate of CO2 formation was faster in 1.0 × 10-1 M than in 1.0 M solutions of methanol, reflecting the concentration dependence of surface poisoning. In 1.0 M methanol solutions, adsorbed CO was observed at hydrogen adsorption and double layer potentials up to the high-temperature limit of the experiments (70 °C).