Transient analysis of polymer electrolyte fuel cells

A three-dimensional, transient model has been developed to study the transient dynamics of polymer electrolyte fuel cell (PEFC) operation. First, various time constants are estimated for important transient phenomena of electrochemical double-layer discharging, gas transport through the gas diffusion layer (GDL) and membrane hydration. It is found that membrane hydration occurs over a period of 10 s, the gas transport of 0.01-0.1 s, with the double-layer discharging being negligibly fast. Subsequently, extensive numerical simulations, with the transient processes of membrane hydration and gas transport taken into consideration, are carried out to characterize the dynamic response of a singe-channel PEFC with N112 membrane. The results show that the time for fuel cells to reach steady state is in the order of 10 s due to the effect of water accumulation in the membrane, consistent with theoretical estimation. In addition, overshoot or undershoot of the current densities is found during the step changes in some operating conditions, and detailed results are provided to reveal the dynamic physics of these phenomena.