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

The elect ro-oxidations of methanol and formic acid at a Ru(0001) electrode in perchloric acid solution have been investigated as functions of tempera ture, potential and time using in-situ FTIR spectroscopy, and the results c ompared to those obtained during our previous studies on the adsorption and electro-oxidation of CO under the same conditions. It was found that no di ssociative adsorption or electro-oxidation of methanol takes place at the R u(0001) at potentials < 800 mV vs. Ag/AgCl, and at all three temperatures e mployed, 10, 25 and 50 degreesC. However. formic acid did undergo dissociat ive 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 de greesC markedly increased the amount of COL formed on the Ru(0001) surface from the adsorption of formic acid. On increasing the potential, the electr o-oxidation of the COL species to CO2 took place via reaction with the acti ve (3 x 1)-O oxide. At all three temperatures employed, it was found that t he formic acid was oxidised to CO2 faster than was observed in the experime nts involving CO adsorbed from CO(g) over the potential range at which oxid ation of COL was observed, suggesting a higher mobility of the COL species formed from the adsorption of the HCOOH. At potentials > 1000 mV, the oxida tion of formic acid to CO2 was significantly increased, and the oxidation o f methanol to CO2 and methyl formate was observed. both of which were attri buted to the formation of an active RuO2 phase on the Ru(0001) surface.