Measurements of permeability and effective in-plane gas diffusivity of gas diffusion media under compression

A novel experimental setup, based on a diffusion bridge, is proposed to accurately and simultaneously measure the in-plane permeability and effective molecular diffusivity of gas diffusion layers used in PEMFC under compression. The permeability is measured by introducing nitrogen in one channel, forcing the gas through the porous media, and measuring pressure drop at various flow rates. To measure effective diffusivity, nitrogen and oxygen are introduced in two channels separated by a porous media. The flow rate of the gases are controlled by two mass flow controllers. The absolute pressure of nitrogen in the channel is controlled by a back pressure controller. The ratio of convection and diffusion flux is modified by controlling the pressure difference between the gases using a differential pressure controller, connected to the oxygen channel. The oxygen mole fraction in the nitrogen channel is meaured at various differential pressures. A steady state one dimensional Fick - Darcy model is used to estimate the permeability and effective molecular diffusivity based on the experimental data. Toray 090 samples with 0 and 40% PTFE at four compression levels are studied. The permeability and diffusibility (ratio of effective to bulk diffusivity) are found to be between 0.98x10(-11) and 0.13x10(-11) m(2), and, 0.52 and 0.09 respectively and are shown to decrease with compression and PTFE.