Assessing durability of cathodes exposed to common air impurities

Data are presented to quantify how common air non-condensable impurities such as NO 2, SO 2, and H 2S 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 NO 2. Complete recovery of the cell performance is obtained after applying neat air following exposure to a total NO 2 dosage of 61.8 μmol. However, to completely recover the cathode exposed to either 118.5 μmol SO 2 or 2160 μmol H 2S, 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 NO 2 does not strongly depend on NO 2 bulk concentration but the rate of SO 2 poisoning of the cathode appear to be strongly dependent on the concentration of SO 2 in the bulk. Relatively high concentrations of impurities were used and the data also show that the cell performance could be totally recovered from NO 2 in neat air after repetitive cycles of exposure/no exposure of 5 ppm NO 2 for 12 h for three cycles (185.4 μmol total dosage). On the other hand, only partial recovery from 5 ppm SO 2 was observed in each cycle and the performance continued to decrease in all the five poisoning cycles (592.5 μmol total dosage).