Transient analysis of reactant gas transport and performance of PEM fuel cells

The dynamic performance of PEM fuel cells is one of the most important criteria in the design of fuel cells with application to mobile systems. To study this issue, we extend our previous steady model of gas reactant transport to an unsteady one and employ it to examine the transient transport characteristics and the system performance of the PEM fuel cells. With the assumption of the two-dimensional mass transport in the cathode side of PEMFC, the effects of the channel width fraction, λ=ℓc/ℓb, the porosity of the gas diffuser layer, ɛ1, and the surface overpotential of the catalyst layer, η, on the transient characteristics of the resultant current density and mass transport are focused in this work. It is disclosed that an increase in λ, or η may lead to a faster dynamic response for the fuel cell when the PEM fuel cell system is started up. Results of a typical case demonstrate that, although the dynamic response time may be as long as 10 s due to the mass transport lag, the fuel cell system needs only less than 0.4 s to reach the 90% response.