Effect of temperature on the mechanism of ethanol oxidation on carbon supported Pt, PtRu and Pt_3Sn electrocatalysts

摘要

The electrochemical oxidation of ethanol on carbon supported Pt, PtRu and Pt_3Sn catalysts was studied in acid solutions at room temperature and in direct ethanol fuel cells (DEFC) in the temperature range 70-100 deg C. In all the experiments, an enhancement of the activity for the ethanol oxidation was observed on the binary catalysts. In acid solution the improvement at low current densities was higher on PtRu than on Pt_3Sn. In DEFC tests, at 70 deg C the cells with PtRu and Pt_3Sn showed about the same performance, while for T > 70 deg C the cells with Pt_3Sn as anode material performed better than those with PtRu as anode material. The apparent activation energy for ethanol oxidation on PtRu catalyst was lower than on Pt_3Sn, particularly at high cell potentials, i.e. at low current densities. At low temperatures and/or low current densities, the positive effect of Ru oxides on the bifunctional mechanism determined the enhancement of activity for the ethanol oxidation reaction, while at high temperatures the positive effect of Sn alloying (enlarged lattice parameter) on CH_3CH_2OH adsorption and C-C cleavage prevails.