Water flow in the gas diffusion layer of PEM fuel cells

Water flow through carbon cloth and carbon paper gas diffusion media used for polymer electrolyte membrane fuel cells treated with Teflon was measured. The gas diffusion layer (GDL) media are hydrophobic and it is necessary to apply pressure to force water to penetrate into the pores of these materials. Teflon treatments made the carbon cloth and paper more hydrophobic, no water flowed through the media until pressures of 5-10 kPa were applied to overcome the surface energy of the water/Teflon interface in the largest pores. The largest pores were ∼250 μm in the carbon cloth and ∼40 μm in the Toray carbon paper. The largest pores in a catalyst layer applied to the woven carbon cloth were ∼20 μm. Increasing the applied hydrostatic pressure permitted water to flow through smaller pores in the GDL. Water flows through less than 1% of the void volume in the GDL; the small pores remain free of water and permit gas to get to the catalyst layer.