Correlating Nitrogen Accumulation With Temporal Fuel Cell Performance

The permeability or crossover characteristics of a typical polymeric perfluorosulfonic acid membrane are used for the temporal and spatial estimation of nitrogen concentration along the anode channels of a fuel cell stack. The predicted nitrogen accumulation is then used to estimate the impact of local fuel starvation on stack voltage through the notion of apparent current density. Despite simplifying assumptions on membrane hydration levels, the calibrated model reasonably predicts the response of a 20-cell stack whenever there is no significant liquid water accumulation in the dead-ended anode. Specifically, the predicted voltage decay and estimated anode outlet gas composition are experimentally validated using stack-averaged voltage and a mass spectrometer. This work shows that the crossover of nitrogen and its accumulation in the anode can cause a considerable stack voltage decay and should be considered under high hydrogen utilization conditions.