The effects of sulfur and nitrogen oxide impurities on proton exchange membrane fuel cell performance

The effect of sulfur fuel impurities and common air contaminants on the performance of Proton Exchange Membrane Fuel Cells (PEMFCs) is the topic of this dissertation. This is of an importance to the Membrane Electrode Assembly (MEA) developers as it will provide an insight on the extent of impurities effects at different dosages and concentration levels, as well as providing an understanding of the mechanism of the MEA poisoning with these impurities. A study of H2S poisoning as a H2 fuel impurity on MEAs consisting of Pt and Pt-Ru alloy electrodes is discussed. Steady state polarization curves are reported for each electrode after exposure to 50 ppm H2S at 70°C.; Quantitative studies evaluating the coverage of sulfur species formed on a Pt anode in a PEMFC running under load upon exposure to 5 ppm H 2S/H2 were carried out in-situ using cyclic voltammetry. The change of coverage by sulfur species is shown to be a function of H2S dosage and temperature at 50 and 70°C.; Common air non condensable impurities such as NO2, SO 2, and H2S show a negative effect on the performance of PEMFCs. The severity of the effects of these impurities varies depending on the impurity studied. The severity of the impurities containing sulfur was higher than NO2. Complete recovery of the cell performance is obtained after applying neat air following exposure to a total NO2 dosage of 61.8 mumol. However, to completely recover the cathode exposed to either 118.5 mumol SO2 or 2160 mumol H2S, cyclic voltammetry is required to oxidize the sulfur adsorbed on the Pt. The sulfur species formed on the Pt cathode after exposure to H2S or SO2 are the same; that is strongly and weakly adsorbed sulfur on the Pt.; Finally, impedance results obtained upon exposure of the cathode to SO 2 impurity are presented. This work provides a starting point for studies on the effects of impurities on PEMFCs using impedance spectroscopy.