The Use of Exergetic Efficiency Rate of Change to Evaluate Fuel Cell Performance from Various Fuels

The use of exergetic efficiency rate of change to evaluate fuel cell performance is developed and explained. It is important to understand the maximum possible thermal efficiency a fuel cell system is capable of obtaining on a fuel and then what fraction of this efficiency it actually achieves. The exergetic efficiency rate of change is a natural and instantaneous measure of the change in fuel cell performance occurring at any time. There are three central performance measures for fuel cells. The first is exergetic efficiency which is measured by thermal efficiency. It permits the direct comparison of the performance of all fuel cell types operating on the same fuel, if desired. The second is exergetic efficiency rate of change which is useful in degradation and which is a broader, more inclusive concept than rate of change of ASR. The third is power or power density which can be related to the economic viability of the fuel cell or fuel cell system. Fuel cell system design and operation is ultimately the resolution of the tradeoffs between the three performance measures.