An experimental set up based on a diffusion bridge is developed to accurately determine the in-plane and through-plane permeability, Knudsen diffusivity and effective molecular diffusivity of gas diffusion layers used in PEFC. The parameters are estimated under various compression levels in in-plane direction. The effect of PTFE on transport parameters is studied in both directions while effect of MPL is studied only in through plane direction. In order to estimate permeability, nitrogen is introduced in one channel, passed through the porous sample, and the pressure drop is measured. Knudsen diffusivity is measured by conducting the permeability experiments with gases of different mean paths i.e. nitrogen and helium. The difference in permeability results was attributed to Knudsen slip.

To measure diffusivity, nitrogen and oxygen are introduced in two channels separated by the porous media. By applying a pressure differential between the channels, ratio of convection and diffusion is modified, and the oxygen concentration is measured in the nitrogen channel. Permeability and effective molecular diffusivity are estimated from pressure drop and oxygen concentration measurements using a one-dimensional mass transport model.

In this study, a steady state Fick's and Darcy's law model is used for gas diffusion layers while Modified Binary Friction Model is used for GDL+MPL assembly for through plane direction. Permeability and effective diffusivity are measured for SIGRACET SGL and several Toray samples with different PTFE loading. Results show that in-plane permeability reduces with compression and amount of PTFE in porous media. In-plane diffusivity decreases with compression, due to decreasing porosity, and with increasing PTFE content. Through plane permeability, Knudsen diffusivity and effective diffusivity also decreases with PTFE content. Coating of an MPL on GDL samples introduces significant Knudsen slip, increasing amount of PTFE in the presense of MPL also reduces permeability, Knudsen diffusivity and effective diffusivity of porous media.