Temperature effects on methanol dissociative chemisorption and water activation at polycrystalline platinum electrodes

A thermostated IR spectroelectrochemical cell was used to probe the effects of temperature (25 - 70 degreesC) and methanol concentration (1.5 x 10(-2) - 1.0 M) on methanol dissociative chemisorption at platinum electrodes in 0.1 M HClO4. The measurements provide molecular level evidence for mechanis ms derived from electrochemical studies of methanol oxidation at above ambi ent temperatures. For fixed methanol concentrations, increasing the tempera ture lowered the quantity of detectable adsorbed CO and increased the rate of CO2 formation. The results can be understood in terms of the thermal act ivation of water and CO desorption. At fixed temperature, raising the metha nol concentration in solution increased the integrated intensities of the a dsorbed CO vibrational bands between 0.2 and 0.7 V (versus reversible hydro gen electrode, RHE). Below 0.9 V, the rate of CO2 formation was faster in 1 .0 x 10(-1) M than in 1.0 M solutions of methanol, reflecting the concentra tion dependence of surface poisoning. In 1.0 M methanol solutions, adsorbed CO was observed at hydrogen adsorption and double layer potentials up to t he high-temperature limit of the experiments (70 degreesC).