Framework for Analysis of Irreversible Fuel Cell Heat Engine Hybrids

Monday, 27 July 2015
Hall 2 (Scottish Exhibition and Conference Centre)
M. C. Williams (URS), R. Gemmen (U.S. Department of Energy, NETL), and K. Gerdes (U.S. DOE, National Energy Technology Laboratory)
A thermodynamic and electrochemical framework for the analysis of the degrading fuel cell heat engine hybrid is developed and explored for various working reactions.  Fuel cell hybrids are a combination of energy conversion sub-systems – fuel cells and heat engines.  Fuel cell hybrids are important for the future for they are the most efficient devices when converting chemical energy of methane from natural gas and renewable fuels to electricity. While the perfect fuel cell would undergo no degradation, practical fuel cells with irreversibilities will degrade.   The common practice is to linearize degradation. However, experimental evidence shows that ASR(t) is commonly an ohmic parabolic function.   By the principle of superposition one can easily develop the equations for degrading hybrids from those developed for hybrids.  The path of maximum power can be developed for degrading hybrids as a function of ASR and temperature. The maximum power for a degrading fuel cell hybrid is given by the Gaussian hypergeometric function. The range of the operation of the SOFC is likely most conducive to hybrid operation for hydrogen oxidation as the working reaction. Each working reaction has a characteristic transition temperature and a characteristic optimal operating temperature.