EFFECT OF NON-UNIFORMLY DISTRIBUTED POROSITY OF GAS DIFFUSION LAYERS ON MASS TRANSFER IN PROTON EXCHANGE MEMBRANE FUEL CELLS

Abstract

Gas diffusion layer porosity can affect mass and charge transfer inside proton exchange membrane fuel cells and influence cell performance. Moreover, the electrochemical reaction rate distribution in various regions inside the cell is not uniform. Proper porosity distribution is very important to improve cell performance. In this paper, a three-dimensional fuel cell model with three steps porosity along the gas flow direction is established. Four cases of non-uniformly distributed porosity, both in anode and cathode gas diffusion layers are simulated, which are compared with uniform porosity distribution to study the effect of these structures on mass transfer inside the cell. Then, an optimization calculation is carried out to obtain the optimal porosity distribution along gas flow direction at 0.2 V and 0.6 V. The numerical results indicate that non-uniformly distributed porosity can change cell performance, and porosity increasing along the gas flow direction makes cell performance be better. Porosity increasing along the gas flow direction can improve the uniformity of current density distribution at low voltage. Diffusive mass flux plays a dominant role in reactant mass transfer. Higher porosity near the outlet region increases total mass flux at the interface, and the proportion of diffusion mass flux in total mass flux also increases.