Modeling of water transport in the membrane-electrode assembly of the proton exchange membrane fuel cell

A computational and experimental joint study of the proton exchange membrane fuel cell (PEMFC) is conducted. The latest modeling works and the technology advancements of the PEMFC are reviewed. Modeling of water transport in PEMFC is the focus of this study. Fuel cell operation faces the dilemma of controlling the amount of water in the cell. It has been shown that the cathode gas diffusion layer (GDL) imposes the mass transport limit by blocking the reactant supply at high current density conditions. So, it is desirable to dissipate water efficiently. On the other hand, the proton exchange membrane (PEM) used today must be humidified to achieve acceptable electrical conductivity. The presence of water benefits the cell performance. Thus, thermal and water management is vital for fuel cell operation in order to maintain certain levels of water within the cell. Considering the significance of these two components (GDL and PEM) in water management, one analytical model is constructed for each component, respectively. For GDL, a separate flow model (SFM), in conjunction with the non-isothermal multicomponent transport model, is used for calculation of the transport phenomena. An analytical solution is obtained for the transport equations, and numerical experiments are conducted. A micro-porous layer (MPL) has been used as a means for water management by applying it to the backing layer (BL). The numerical results suggest that optimal parameters exist when the MPL/BL is used, and an optimal MPL particle diameter is found to be 1 micron. For PEM, an analytical solution is derived for the Nernst-Plank equation, which models both diffusion and electro-osmosis of water in PEM. The general analytical solution is obtained for the vapor-equilibrated membrane. The analytical results agree well with the numerical results. These two models provide physically sound tools to allow fast design and prototyping of PEMFC.