Evaluation of a 2.5 kWel automotive low temperature PEM fuel cell stack with extended operating temperature range up to 120°C

Nowadays, the operating temperature of polymer electrolyte membrane fuel cell stacks is typically limited to 80 degrees C due to water management issues of membrane materials. In the present work, short-term operation at elevated temperatures up to 120 degrees C and long-term steady-state operation under automotive relevant conditions at 80 degrees C are examined using a 30-cell stack developed at DLR. The high temperature behavior is investigated by using temperature cycles between 90 and 120 degrees C without adjustment of the gases dew points, to simulate a short-period temperature increase, possibly caused by an extended power demand and/or limited heat removal. This galvanostatic test demonstrates a fully reversible performance decrease of 21 +/- 1% during each thermal cycle. The irreversible degradation rate is about a factor of 6 higher compared to the one determined by the long-term test. The 1200-h test at 80 degrees C demonstrates linear stack voltage decay with acceptable degradation rate, apart from a malfunction of the air compressor, which results in increased catalyst degradation effects on individual cells. This interpretation is based on an end-of-life characterization, aimed to investigate catalyst, electrode and membrane degradation, by determining hydrogen crossover rates, high frequency resistances, electrochemically active surface areas and catalyst particle sizes. (C) 2015 Elsevier B.V. All rights reserved.