The electro-oxidations of methanol and formic acid at the Ru(0001) electrode as a function of temperature: in-situFTIR studies

Abstract

The electro-oxidations of methanol and formic acid at a Ru(0001) electrode in perchloric acid solution have been investigated as functions of temperature, potential and time using in-situ FTIR spectroscopy, and the results compared to those obtained during our previous studies on the adsorption and electro-oxidation of CO under the same conditions. It was found that no dissociative adsorption or electro-oxidation of methanol takes place at the Ru(0001) at potentials <800 mV s. Ag/AgCl, and at all three temperatures employed, 10, 25 and 50°C. However, formic acid did undergo dissociative adsorption, even at − 200 mV, to form linearly adsorbed CO, (CO_L), with little or no CO adsorbed at threefold-hollow sites, (CO_H). In contrast to the adsorption of CO, it was found that increasing the temperature to 50°C markedly increased the amount of CO_L formed on the Ru(0001) surface from the adsorption of formic acid. On increasing the potential, the electro-oxidation of the CO_L species to CO₂ took place ia reaction with the active (3 × 1)-O oxide. At all three temperatures employed, it was found that the formic acid was oxidised to CO₂ faster than was observed in the experiments involving CO adsorbed from CO(g) over the potential range at which oxidation of CO_L was observed, suggesting a higher mobility of the CO_L species formed from the adsorption of the HCOOH. At potentials >1000 mV, the oxidation of formic acid to CO₂ was significantly increased, and the oxidation of methanol to CO₂ and methyl formate was observed, both of which were attributed to the formation of an active RuO₂ phase on the Ru(0001) surface.