E.J. Park, K.H. Lim, S. Maurya, S. Adhikari, C. Bae, J.F. Brennecke, I. Matanovic, E.S. DeCastro, H. Jia, Y.S. Kim
Los Alamos National Laboratory,
Keywords: fuel cells, high temperature proton exchange membrane, ion-pair, phosphonated ionomers, heavy duty truck
Summary:A fuel cell uses chemical energy of hydrogen to cleanly and efficiently produce electricity. Current state-of-the-art fuel cells for automotive applications use perfluorosulfonic acids, only allowing the operation under low temperature (< 100 °C) and humidified conditions. We use ion-pair coordinated membranes, which exhibit stronger interaction than acid-base interaction of phosphoric acid-doped polybenzimidazole membranes, to substantially improve water tolerance and thermal stability. The use of ion-pair coordinated membranes along with phosphonated ionomers in the electrode allows operation of fuel cells at higher temperatures (> 100 °C) without external humidification. The operation at elevated temperature offers numerous advantages including heat and power co-generation, high tolerance to impurities in fuels, and a simple system design, thus significant cost reduction can be achieved. Our technology is targeting heavy-duty vehicle (HDV) applications. One of the most significant technical challenges of HDV fuel cells is heat rejection. In current low-temperature fuel cells, the temperature difference between the fuel cell operating temperature (60-80 °C) and ambient temperature is relatively small when compared with internal combustion engines, and this small temperature difference poses a significant challenge for designing a small and lightweight cooling system. The heat rejection requirement is met by operating the fuel cell at a high cell voltage, 0.76 V at 80 °C, where the power generated is < 0.45 W cm-2. If fuel cells can operate above 100 °C, the heat rejection issue is much lessened, and the power generation can be increased. Our ion-pair technology is designed to operate fuel cell at 160 °C, where the power generated is 0.78 W cm-2, ~1.7 times higher than the rated power of state-of-the-art low-temperature fuel cells. Comparing with state-of-the-art polybenzimidazole-based high-temperature fuel cells, which are inoperable after 30 thermal cycles (80-160 °C) under 30 kPa water vapor pressure. Our ion-pair-based fuel cell does not show any sign of degradation after 680 thermal cycles under the same testing conditions. The high water tolerance makes the ion-pair fuel cells suitable for HDV automotive applications.