Absolute permeability and Knudsen diffusivity measurements in PEMFC gas diffusion layers and micro porous layers

A novel approach for predicting absolute permeability and effective Knudsen diffusivity values in gas-diffusion-layers/microporous layers (GDLs/MPLs) is proposed. A conventional diffusion bridge setup with modifications is used to obtain the pressure drop across the GDL at several mass flow rates. The experimental results are then fitted to both the Darcy's model and the binary friction model (BFM). Experimental data obtained using different working gases, e.g. O2, N2, He and Ar, are used to validate the two model predictions. Experimental results show that the traditionally used Darcy's law is not able to predict the pressure drop across the GDL, especially in a GDL with an MPL, due to Knudsen effects. The BFM accounts for both viscous and Knudsen transport and it is thereby shown to provide more accurate predictions for any working fluid tested. Permeability and effective Knudsen diffusivities obtained using both Darcy's model and BFM for a SGL (Weisbaden, Germany) SIGRELET 34BA and 34BC are reported.

► Experimental setup to measure through-plane absolute permeability.
► Permeability of gas-diffusion-layers/microporous layers (GDLs/MPLs) is obtained using different working fluids.
► The validity of Darcy's model in gas-diffusion-layers/microporous layers (GDLs/MPLs) is assessed using several working fluids.
► The binary friction model is used to estimate permeability and Knudsen diffusivity.
► Absolute permeability and Knudsen diffusivity reported for SGL 34BA and 34BC.