Development and Characterization of a LT-PEMFC Stack with an Extended Operating Temperature Range up to 120 °C

Kurzfassung

Nowadays, the operation temperature of a polymer electrolyte fuel cell (PEFC) stack for automotive application is about 80 °C. The presented work concerns the characterization of a 30-cell PEFC stack (2.5 kWel) developed at the German Aerospace Center, designed for operating temperatures up to 120 °C for a limited time span. Short-term operation of the stack at higher temperatures would contribute to the improvement of cooling system components with scaled-down dimensions. This concept helps to reduce the vehicle weight and thus to save fuel. In this contribution we present a proof-of-concept of the feasibility of short-term operation for excess temperature events. For this purpose, the stack behaviour was investigated through a series of 20 temperature cycles from 90 to 120 °C at galvanostatic conditions of 70 A (approx. 0.5 A·cm–2 and 1.5 kWel) and without adaption of the gas dew points. The stack power decreased by 21 ± 1 %, with a fully reversible performance recovery at the end of every thermal cycle (see Fig. 1). The higher irreversible degradation rate under these harsh conditions was attributed to the enhanced mechanical stress, which is also correlated to the cycling of the membrane humidity. Furthermore, the results of a long-term steady-state test of 1200 hours under automotive relevant conditions at 80 °C are presented. An end-of-life characterization of the individual cells helped to identify possible causes for performance losses due to catalyst, electrode and membrane degradation. A reduction of electrochemically active surface areas in some cells was ascribed to a platinum catalyst particle growth. Membrane degradation and carbon corrosion occurred additionally, evidenced by increased high frequency resistances and hydrogen crossover rates of the membranes. As result of carbon corrosion, the hydrophobicity of the carbon-based components decreased, causing water accumulation in individual cells.