The operational strategy for a solid oxide fuel cell undergoing degradation is investigated in this paper. While the perfect fuel cell would undergo no degradation, practical fuel cells of any type (e.g., polymer electrolyte, etc.), like batteries, will degrade. For fuel cells, dominant mechanisms of degradation will depend on materials of construction, operating conditions, and operational history. The common practice is to linearize degradation. Giving a linear representation to degradation rate, however, gives a linear structure to the area specific resistance, ASR(t). Experimental evidence shows that ASR(t) is commonly a parabolic function. Four important operational strategies are evaluated for degrading fuel cells - constant voltage, constant current, maximum power, and constant design power. This work demonstrates that degrading fuel cells exhibit a natural exergetic efficiency for a given fuel utilization. This exergetic efficiency is constant along the path of maximum power. To operate at this exergetic efficiency is to operate along the path of maximum power. The path of maximum power can be pursued as an operational strategy by varying the fuel flow rate (fuel cell current) at constant fuel utilization. A separate question of possible concern is what is the maximum allowable current.
展开▼
