Ethanol electrooxidation on a carbon-supported Pt catalyst at elevated temperature and pressure: A high-temperature/high-pressure DEMS study

The electrooxidation of ethanol on a Pt/Vulcan catalyst was investigated in model studies by on-line differential electrochemical mass spectrometry (DEMS) over a wide range of reaction temperatures (23-100 degrees C). Potentiodynamic and potentiostatic measurements of the Faradaic Current and the CO2 formation rate, performed at 3 bar overpressure under well-defined transport and diffusion conditions reveal significant effects of temperature, potential and ethanol concentration on the total reaction activity and on the selectivity for the pathway toward complete oxidation to CO2. The latter pathway increasingly prevails at higher temperature, lower concentration and lower potentials (similar to 90% current efficiency for CO2 formation at 100 degrees C, 0.01 M, 0.48 V). while at higher ethanol concentrations (0.1 M), higher potentials or lower temperatures the current efficiency for CO2 formation drops, reaching values of a few percent at room temperature. These trends result in a significantly higher apparent activation barrier for complete oxidation to CO2 (68 +/- 2 kJ mol(-1) at 0.48 V, 0.1 M) compared to that of the overall ethanol oxidation reaction determined from the Faradaic current (42 +/- 2 kJ mol(-1) at 0.48 V, 0.1 M). The mechanistic implications of these results and the importance of relevant reaction and mass transport conditions in model studies for reaction predictions in fuel cell applications are discussed. (C) 2009 Elsevier B.V. All rights reserved.