Development and Characterization of a LT-PEM Fuel Cell Stack with Wide Operating Temperature Range up to 120 °C

Kurzfassung

The typical operating temperature range of a polymer electrolyte membrane fuel cell (PEMFC) stack for automotive application lies between –20 °C and 80 °C [1,2]. Nevertheless, the feasibility to operate in a broader temperature range can be of particular relevance to meet specific environmental or operative conditions. Two possible scenarios include vehicles running in hot areas like deserts, and long uphill drive (e.g. during mountain driving), which require higher power with simultaneous slow average speed, and thus with minimized air cooling. 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 for the stack to temporarily operate at higher temperature, would also 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 wide operating temperatures, we performed a series of 20 temperature cycles from 90 to 120 °C, operating in galvanostatic conditions at a controlled current of 70 A (0.5 A/cm2), that correspond to an electrical stack power output of approx. 1.5 kW. The results are promising, since only a slight stack voltage decrease was observed during the thermal cyclization. Furthermore, the results of a 1200 h long-term stability test are shown, together with an end-of-life electrochemical characterization (cyclic voltammetry and hydrogen crossover measurements) performed on all the cells. The electrochemical analysis can help to identify the main stressors responsible for the observed stack performance loss. Therefore, the catalyst, electrode and membrane degradation are examined by the determination of hydrogen crossover rates, electrochemically active surface areas (EASAs) and electrical short-circuit resistances of each cell. REFERENCES [1] Wu J.F., Yuan X.Z., Martin J.J., Wang H.J., Zhang J.J., Shen J., Wu S.H., Merida W., 2008, A review of PEM fuel cell durability: Degradation mechanisms and mitigation strategies, J. Power Sources, vol. 184, n° 1: pp. 104-119.[2] Schießwohl E., von Unwerth T., Seyfried F., Brüggemann D., 2009, Experimental investigation of parameters influencing the freeze start ability of a fuel cell system, J. Power Sources, vol. 193, n° 1: pp. 107-115.