A PEMFC Stack with Extended Operating Temperature Range up to 120 °C

Kurzfassung

The normal operating temperature range of a polymer electrolyte membrane fuel cell (PEMFC) stack for automotive application lies between –20 °C and 80 °C. Safe freeze start should be possible down to –30 °C [1], while the start-up time of the fuel cell vehicle should be clearly shorter than a minute, or better just a few seconds. However, in most climatic regions the temperature stability of the stack at higher temperatures is even more interesting to be explored, in order to meet specific environmental or operative conditions. The work presented here concerns the characterization of a 30-cell PEMFC stack developed at the German Aerospace Center designed for operation in an extended temperature range up to 120 °C. The feasibility to operate in a broader temperature range can be of particular relevance in two possible scenarios, represented by vehicles running in hot areas like deserts, or by long uphill drive (e.g. during mountain driving) that requires higher power with simultaneous slow average speed, and thus with minimized air cooling. This would contribute to the improvement of cooling system components with scaled down dimensions, which in turn would lead to a reduced vehicle weight and thus to an overall lower fuel consumption. In this contribution we present the current-voltage characteristic curves measured on the 30-cell stack and the homogeneity obtained along the cells. Moreover, in order to investigate the stack behaviour at extended operating temperatures, we performed a series of 20 temperature cycles from 90 to 120 °C, operating at a galvanostatic controlled current of 70 A, that corresponded to an electrical stack power output of approx. 1.5 kW. The results are promising, since only a slight stack voltage decrease was observed. Furthermore, the results of a 1000 h long-term stability test are shown, whose focus lies on the evaluation of the possible lifetime and the related overall cells degradation. Literature: [1] E. Schießwohl et al., J. Power Sources 2009, 193, 107-115.