Methanol Oxidation Over a Pt/C Catalyst at High Temperatures and Pressure: An Online Electrochemical Mass Spectrometry Study

The influence of elevated reaction temperatures (up to 100 degrees C) on the characteristics of the methanol electrooxidation reaction over carbon-supported Pt catalysts was investigated by high-temperature/high-pressure differential electrochemical mass spectrometry (HT/HP DEMS), at up to 100 degrees C and 3 bar overpressure. The total reaction rate and that for CO2 formation were followed by potentiodynamic and potentiostatic measurements, performed under fuel cell relevant, but nevertheless well-defined, reaction and transport conditions. Activation energies for the overall methanol oxidation process and for the specific pathway to CO2 formation as well as the current efficiency for CO2 production were determined over a wide range of potentials and temperatures; the influence of the electrolyte flow rates and of the catalyst loading was tested. Most important, the apparent activation energies for CO2 formation were generally larger than those for the overall reaction, leading to an increasing selectivity for CO2 formation with temperature and complete conversion to CO2 at similar to 100 degrees C reaction temperature under present reaction conditions. The resulting trends are discussed in a mechanistic picture, including transport effects. Consequences for applications in direct methanol fuel cells (DMFCs) are discussed.