Analytical Solution for Two-Phase Flow in PEMFC Gas Diffusion Layer

Thermal and water management is critical to fuel cell performance. It has been shown that gas diffusion layer (GDL) can impose the mass transport limit; for example, it can block the reactant transport to active layer when flooding occurs at high current density conditions. Micro porous layer (MPL) in conjunction with backing layer (BL) has been used as a GDL material and was shown to be effective for water management. To study the transport processes in GDL and MPL modified GDL, an analytical solution is derived current study for calculation of two-phase, multicomponent transport in GDL. Two models were considered, the unsaturated flow model (UFM) and the separate flow model (SFM). Comparison of the calculated saturation level and oxygen mass fraction shows that UFM calculation can underestimate, as well as overestimate the saturation and oxygen concentration. The SFM was used to study the effects due to GDL property variations. The calculation shows that increase in liquid water transport in an MPL modified GDL is due to the abrupt change of liquid water flow rate when a step change in porosity or permeability is imposed. The calculation further shows that particle size of around 1 μm would be a good choice for MPL as it results in higher oxygen concentration at active layer and lower saturation in GDL.