Impact of Hydrogen Fuel Impurities on PEMFC Performance

Concerning carbon monoxide, hydrogen sulfide and ammonia, which are likely to be present in hydrogen fuel as impurities, a study was conducted to evaluate the impact of these impurities on the performance of proton exchange membrane fuel cells (“PEMFC”). The study involved a fuel cell performance test using a single cell and the analysis of exhaust gases from the cell. The fuel cell was operated continuously for 10 hours under acceleration test conditions at a 1,000 mA/cm² current density and a 17 % fuel gas utilization. The results: the cell performance declined when any of the three impurities was present at lower than ppm content levels (0.2 - 0.5 ppm) in hydrogen fuel. Pt-Ru alloy catalysts, known for their higher resistance than Pt to poisoning by carbon monoxide, failed to show improvement of resistance to poisoning by hydrogen sulfide and ammonia. The cell performance decline caused by hydrogen sulfide proved irreversible in that the declined performance could be recovered only partly despite the supply of high-purity hydrogen. However, when the cell was maintained at the open circuit voltage while supplying high-purity hydrogen, the lowered cell performance did markedly recover because sulfur species were desorbed as hydrogen sulfide from the Pt catalyst. Regarding the effect of ammonia, the deteriorated performance caused by ammonia regained its initial level at the supply of high-purity hydrogen, though it was much slower than the case of carbon monoxide. Also, it was revealed by exhaust gas measurement that ammonium ions existed not only in anode exhaust gas but also in cathode emissions.