Assessing durability of cathodes exposed to common air impurities

Data are presented to quantify how common air non-condensable impurities such as NO2, SO2, and H2S show a negative effect on the performance of PEMFCs. The severity of the effects of these impurities varies depending on the impurity, concentration, and dosage but in general the impurities containing sulfur showed a stronger effect 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 these impurities appear to be the same and it appears as strongly and weakly adsorbed sulfur on the Pt. The data show that the rate of poisoning of PEMFCs by NO2 does not strongly depend on NO2 bulk concentration but the rate of SO2 poisoning of the cathode appear to be strongly dependent on the concentration of SO2 in the bulk. Relatively high concentrations of impurities were used and the data also show that the cell performance could be totally recovered from NO2 in neat air after repetitive cycles of exposure/no exposure of 5 ppm NO2 for 12 h for three cycles (185.4 mumol total dosage). On the other hand, only partial recovery from 5 ppm SO2 was observed in each cycle and the performance continued to decrease in all the five poisoning cycles (592.5 mumol total dosage). (C) 2004 Published by Elsevier B.V.