The Impact of Trace Carbon Monoxide / Toluene Mixtures on PEMFC Performance

The impact of fuel impurities toluene (C7H8) and carbon monoxide (CO) on the performance of polymer electrolyte membrane fuel cells (PEMFCs) was investigated. Single and mixed impurities were injected into the fuel cell via the anode feed stream. Experiments were accompanied by gas chromatography analysis to determine the conversion and reaction processes occurring during contaminant exposure. Impurity injections of 2 and 20 ppm C7H8 caused an insignificant overpotential change of 2 and 8 mV respectively. An almost complete conversion of C7H8 to methylcyclohexane (C7H14) was observed. Impurity injections of 2 ppm CO caused a significant overpotential change of 247 mV. At steady state conditions more than 60% of the injected CO was converted to CO2 in the fuel cell. When the impurities were injected into the anode feed stream as a mixture the overpotential change was 100 mV greater than the sum of the overpotential changes the single impurities caused .Hydrogenation of C7H8 to C7H14 was observed but in contrast to the single C7H8 impurity experiment it stopped when a certain CO coverage was reached. The strong adsorption of CO caused a competition between the hydrogen reduction reaction and the hydrogenation of C7H8 for the available reaction sites.