Water Flow in, Through, and Around the Gas Diffusion Layer

Liquid water produced in polymer electrolyte membrane fuel cells is transported from the cathode catalyst/membrane interface through the gas diffusion layer (GDL) to the gas flow channel. Liquid water travels both laterally (in the plane of GDL) and transversely through the largest pores of the porous GDL structure. Narrow apertures in the largest pores are the primary resistance to liquid water penetration. Carbon paper has limiting apertures ∼20 μm in diameter and ∼1 μm in length whereas carbon cloth has apertures ∼100 μm in diameter and ∼200 μm in length. After sufficient hydrostatic pressure is applied, water penetrates the limiting aperture and flows through the pore. The pressure required for water to flow through the pores is less than the pressure to penetrate the limiting aperture of the pores. Water moved laterally and directed through a small number of transverse pores. There is less resistance to lateral liquid water flow at the interface between the GDL and a solid surface than through the GDL. The results from these experiments suggest that water flow through the GDL is dominated by a small number of pores and most pores remain free of liquid water.