Mechanical Engineering, Sharif University of Technology
Gas diffusion layers are essential components of proton exchange membrane fuel cell since the reactants should pass through these layers. Mass transport in these layers is highly dependent on porosity. Many of simulations have assumed, for simplicity, the porosity of GDL is constant, but in practice, there is a considerable variation in porosity along gas diffusion layers. In the present study the porosity variation in GDL is calculated by considering the applied pressure and the amount of water generated in the cell. A two dimensional mathematical model is developed to investigate the effect of stack compression and water generation on porosity of GDL and cell performance. The validity of the model is assessed by comparing the computed results with experimental data. The results show that when the electrical current density is low, the porosity variation in the gas diffusion layer has no significant influence on the level of polarization whereas at higher current density the influence is very significant. It is also shown that, the electrical current has a sharp gradient across the catalyst layer. Therefore, the better cell performance could be achieved by adding a certain amount of catalyst loading to each electrode, with respect to the reactant concentration.