Temperature Effect on Methanol and Ethanol Electrooxidation at Pt/C and Pt-Ru/C Microporous Electrodes

Temperature effect on methanol and ethanol electrooxidation was investigated with cyclic voltammetry at carbon supported Pt and Pt-Ru microporous electrodes. In methanol solution, the currents were enhanced by 10 and 20 times at Pt/C and Pt-Ru/C, respectively in the temperature range from 25°C to 80°C. With increasing temperature at both electrodes, decreases in the potential difference of oxidation peaks at positive and negative potential scanning were observed, indicating that OH adsorption on the catalysts affects methanol oxidation and bifunctional mechanism is active. Especially, vertically increased oxidation peak during negative potential scanning was observed at Pt/C, presumably due to the weak OH adsorption on the platinum surface. The effect of ruthenium addition on the poisoning reduction was also confirmed. In ethanol solution, Pt/C increased currents only by a factor of 4 whereas Pt-Ru/C raised it about 8 times for the same temperature range. Lower temperature dependence of currents in the ethanol solution is probably caused by weaker OH adsorption in the ethanol solution than in the methanol solution. The ruthenium addition remarkably enhanced ethanol oxidation performance probably due to the strong adsorption of OH. In both alcohols, Pt-Ru/C showed larger apparent activation energies of oxidation than Pt/C, representing higher temperature dependence of OH adsorption on ruthenium.