WATER TRANSPORT IN THE MEA OF A PEM FUEL CELL

In the paper, a one-dimensional model of water transport across the entire cell is presented for the proton exchange membrane fuel cell. In the model, the catalyst layer is treated as a separate computing domain, not an interface between the gas diffusion layer and membrane. Meanwhile, in the membrane mechanisms of back diffusion and electro-osmotic drag are considered, while pure diffusion process is taken into account for the gas-phase flow in the cell. In the catalyst layer, except for Knudsen diffusion, water vapor in the pore is coupled with liquid water in the ionomor phase by the isotherm sorption and in equilibrium with each other. The results indicate both the operating pressure and mean current density arc the important factors to affect the water transport process in the cell. Moreover, it is found that the liquid water diffusivity dependent on water content in the ionomer phase would lead to the water content distribution at the different degree nonuniformity. Additionally, the thinner membranes result in the higher and more uniform distribution of water content in the membrane phase. Furthermore, the concentration-gradient driven water flux based on Henry'law is exposed on the anode surface of the membrane as the boundary condition, which is more appropriate to present the reality of water content in the ionomer phase. The numerical results imply that it is very necessary to investigate the interaction among different components of a cell, so as to predict correctly the coupled transport phenomena occurred in the entire fuel cell.