CFD simulation of the transient gas transport in a PEM fuel cell cathode during AC impedance testing considering liquid water effects

This work presents the application of CFD (Computational Fluid Dynamics) to the unsteady gas transport modelling in the cathode side of a Polymer Electrolyte Membrane (PEM) fuel cell during an AC impedance test. The CFD model development and results during AC impedance experiments for 1D and 2D cases are presented and discussed. The effect of liquid water was considered by modelling scenarios with saturated (according to water profiles obtained experimentally) and dry Gas Diffusion Layers (GDL). It was observed that the magnitude of the transient variations of the oxygen concentration within the GDL is dependent on the frequency of the AC signal during the test, given the differences between the diffusion characteristic time and the oxygen consumption characteristic time. For the 2D model where the differences under-the-rib to under-the-channel can be analysed, it was verified that oxygen concentration is much higher under the channel, however the amplitude of the oscillations during AC testing are significantly higher under the rib. When comparing saturated and dry GDLs for both models, it was verified that oxygen concentrations are higher for dry GDLs, but the amplitude of the oscillations is however higher for saturated GDLs.