An analytical relationship for calculating the effective diffusivity of micro-porous layers

Gas diffusion layer, GDL, properties are crucial in determining the polymer electrolyte membrane fuel cell performance. The micro-porous layer, as a thin layer coated on the GDL that has a smaller pore size than the fibrous substrate, creates a considerable mass transport barrier to the incoming gases from the flow channels. Hence, the effective diffusivity of MPL can affect the overall performance of PEM fuel cell. In the present investigation, a new analytical model is developed, based on the unit cell approach, to find the effective diffusivity of the MPL. A compact relationship is proposed that can be used to estimate the effective MPL diffusivity as a function the MPL pore size distribution and porosity. The developed model is also used to find the sensitivity of the aforementioned design parameters on the effective diffusivity. It is found that the MPL pore size is as influential as the porosity on the effective diffusivity.