Membrane degradation in polymer electrolyte fuel cells under low humidification conditions

A durability test of a PEFC single cell using perfluorinated ionomer membrane as an electrolyte was carried out at 80 degrees C under low humidification. The observed voltage drop under low humidification was mostly reversible up to 5200 h. However, hydrogen crossover increased with time and fluoride-ion was continuously detected in drain water, which indicated that membrane degradation proceeded steadily during the test under low humidification. Fluoride-ion release rate decreased with increasing current density, which suggested that hydrogen peroxide was formed at the anode catalyst layer upon direct combustion of hydrogen with crossover oxygen. Drain water analysis revealed that large amounts of sulfate ions and Fe(II or III) ions were released in addition to fluoride ions when the cell was temporarily operated under full humidification. From this fact, it was concluded that accumulation of impurities and hydrogen peroxide under low humidification is a reason why low humidification enhances membrane degradation.