Water Diffusion, Drag and Absorption in an Anion-Exchange Membrane Fuel Cell

Water is a key factor in anion-exchange membrane fuel cells, since it is both a product and a reactant, and humidifies the membrane and the ionomer phase. To optimize the operation conditions preventing cathode drying and anode flooding, better knowledge on the water transport is needed. In this work, the water transport across an Aemion TM membrane is quantified for different applied water partial pressure differences and current densities. Two membrane thicknesses, 25 and 50 μm, are studied, as well as two gas diffusion layers (GDLs) of different hydrophobicity: the hydrophobic Sigracet 25BC treated with polytetrafluoroethylene (PTFE), and Freudenberg H23C2 being hydrophilic as it is not treated with PTFE. The measurements show that having a hydrophilic GDL on both electrodes results in poor electrochemical performance, and restricted water transport. Although the highest water molar flux was observed for hydrophilic GDL on cathode and hydrophobic GDL on anode, the best electrochemical performance was observed for the opposite combination. A water transport model considering absorption/desorption resistance, electroosmotic drag and diffusion was deployed. The best fit of the model to the experimental data was obtained with a water drag coefficient of 2, and almost about 30% difference in absorption/desorption coefficient due to different GDLs.