Modeling the Dynamic Behavior of Proton-Exchange Membrane Fuel Cells

A two-phase transient model has been developed which predicts the dynamic response of Proton-Exchange Membrane Fuel Cells (PEMFCs) to transients in operating power. The model uses experimentally measured Gas Diffusion Layer (GDL) capillary pressure to predict the fuel cell response to changing water production rates. Permanent hysteresis observed in experimentally measured capillary pressure of GDL is examined and found to have minimal effects on the modeling results. The model also provides explanations for the difference in time constants between membrane hydration and dehydration observed in the high frequency resistance (HFR) experiments. When there is liquid water at the cathode catalyst layer, the time it takes the water content in the membrane to reach steady state is closely tied to that of liquid water saturation in the cathode catalyst layer, as the vapor is already saturated. The water content in the membrane does not reach steady state as long as the liquid water flow in the cathode catalyst layer is not at steady state. The effects of membrane thickness on membrane hydration and dehydration time constants are investigated for Nafion 112, 115, and 117.