The electro-oxidations of methanol and formic acid at the Ru(0001) electrode as a function of temperature: in-situ FTIR 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, (COL), with little or no CO adsorbed at threefold-hollow sites, (COH). In contrast to the adsorption of CO, it was found that increasing the temperature to 50°C markedly increased the amount of COL formed on the Ru(0001) surface from the adsorption of formic acid. On increasing the potential, the electro-oxidation of the COL 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 COL was observed, suggesting a higher mobility of the COL 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.