Bistable current-voltage characteristics of PEM fuel cells operated with reduced feed stream humidification

With the help of a simple, spatially lumped, and isothermal model, we qualitatively predict and discuss bistable current-voltage characteristics of proton exchange membrane (PEM) fuel cells operated with low humidified feed gases. The cell is found to exhibit current-voltage curves with pronounced local extrema in a parameter range that is of practical interest when operated at constant feed gas flow rates. This causes steady-state multiplicities in the potentiostatic and rheostatic operation mode. The reason for the predicted behavior is an autocatalytical water production mechanism. For small inlet relative humidities or even no humidification, the current-voltage curve possesses an isolated high-current branch, which was recently observed experimentally. A parameter range is predicted, wherein such current-voltage characteristics can be observed. Furthermore, we review selected experimental studies on this topic and discuss their results against our findings. (c) 2007 The Electrochemical Society.