Temperature effect on the electrode kinetics of ethanol electro-oxidation on Sn modified Pt catalyst through voltammetry and impedance spectroscopy

The effects of temperature and ethanol concentration on the activity of electrodeposited PtSn catalysts towards ethanol oxidation had been investigated. Electro-codeposition from a bath of Pt and Sn precursors led to both alloyed and unalloyed PtSn system depending on the deposition conditions. A study of the temperature dependence of ethanol oxidation in the range of 10-70 degrees C afforded the determination of the activation energies on Pt and PtSn catalyst formulations. The onset potential of ethanol oxidation was lowered by ca. 300 mV for all PtSn catalysts as compared to Pt demonstrating that surface Sn and/or its oxides can provide oxygen species at much lower potentials compared to Pt. The considerable lowering of the activation energy for the unalloyed PtSn catalyst was due to its effectiveness for the coupled processes of dissociative ethanol adsorption and COads oxidation. The appearance of an inductive loop at temperatures >30 degrees C in the Nyquist plots, attributable to CO oxidation, for the unalloyed PtSn catalyst formulation, further demonstrated its ability to mitigate CO poisoning of the electrode surface. The effect of ethanol concentration on the electro-oxidation process was revealed through the determination of apparent reaction order, by the help of voltammetry and impedance studies in the ethanol concentration range of 0.1-1.0 M. (C) 2010 Elsevier B.V. All rights reserved.