Abstract
In the present study, the one dimensional MEA model and three dimensional model for polymer electrolyte membrane(PEM) fuel cell are investigated numerically. The computational domain includes gas channel, gas diffusion layer, catalyst layer and membrane. In the practical application of the PEM fuel cell, liquid water would exist at high current density, it reduces the diffusivity of the gas phase species. Previously, the effective medium theory has been adopted to approximate the gas diffusion layer effective diffusivity, but it tends to overpredict the diffusivity with large water content, and hence with erroneous high cell performance. The present effective diffusivity model is validated by the network model result of fibrous diffusion media with respect to porosity and liquid water saturation. The result of present model can mimic the change of the effective diffusivity in response to the variation of the water saturation levels. The models are further validated by computing two phase flows within the fuel cell and the predicted polarization curves are compared with available measurement. Moreover, the present study also considers the influence of the continuity of capillary pressure with the presence of liquid water and micro-porous layer(MPL). The continuous capillary pressure will cause a discontinuous liquid saturation at the porous media interface by material properties such as contact angle and porosity. In order to analyze this phenomenon, we use an immersed interface method (IIM) in one dimensional two phase MEA model to solve the problems of discontinuous liquid saturation. The numerical results with iso/non-isothermal conditions are compared with experimental data. However, due to the numerical stability problem, the present study only shows results at the region near the limiting current density, the simulations indicate that lower level of oxygen in the cathode catalyst layer, and hence it can not generate higher current density. This however contradicts the commonly observations that the model with MPL has greater current density. The cause of this inconsistency is not clear, and should be investigated further.