Measurement of carbon dioxide yields for ethanol oxidation by operation of a direct ethanol fuel cell in crossover mode

Faradaic yields of carbon dioxide from ethanol oxidation were measured with a non-dispersive CO2 detector for a direct ethanol fuel cell (DEFC) operating in crossover mode with aqueous ethanol delivered to the cathode and N2 passing through the anode compartment. Under these conditions, the rate of ethanol oxidation is limited by its rate of diffusion though the Nafion membrane (crossover). It is shown, by comparison with results obtained with methanol and by running the cell normally, that this experimental configuration provides more accurate results by minimizing the effects of CO2 crossover. The faradaic yield of CO2 was found to increase significantly with decreasing ethanol concentration, reaching 64% for oxidation of 0.1 M ethanol at 80 °C. However, the highest yield (>68%) was obtained by operating the cell normally.

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► Measurement of CO2 in the anode exhaust of a direct alcohol fuel cell underestimates the true CO2 yield due to crossover of CO2 through the membrane.
► Oxidation of ethanol that crosses the membrane, and analysis of CO2 in the anode gas stream, provides higher and more accurate CO2 yields.
► The potential dependence of the CO2 yield for ethanol oxidation varies with the cell operating mode (normal vs. crossover).
► A CO2 yield of >68% was obtained with 0.1 M ethanol at 80 °C.