Evaluation of the Degradation of Fuel Cell Heat Engine Hybrids for Renewable Fuels

Fuel cell hybrids are combination of energy conversion sub-systems—fuel cells and heat engines. Fuel cell hybrids are important for the future as they are currently the most efficient devices when converting chemical energy of methane from renewable fuels to electricity. While the perfect fuel cell would undergo no degradation, practical fuel cells, like batteries, will degrade. This paper is a study of fuel cell hybrids electrochemical performance when the fuel cell sub-system is under- going degradation. In all cases, one can utilize the waste heat to improve overall efficiency through hybridization. Even degradation rates of 0.25 percent per 1000 hours, corresponding to 40,000 hour life, produce significant amounts of waste heat. Power loss is especially high at the cycle end-of- life. Hybridization utilizes waste heat and can be used if degradation occurs and long fuel cell life is expected. The common practice is to linearize degradation. Giving a linear representation to DR, however, gives a linear structure to the area specific resistance, ASR(t). Experimental evidence shows that ASR(t) is commonly an ohmic parabolic function. Degradation rate, DR avg (t), %/1000 hours varies throughout the life of the fuel cell for ohmic parabolic degradation behavior.