Influence of compressive stress on the pore structure of carbon cloth based gas diffusion layer investigated by capillary flow porometry

Gas diffusion layer (GDL) is subjected to compressive stress at high temperature along with polymer electrolyte membrane in the fabrication process and in assembling the fuel cell stacks. Compressive stress decreases the thickness of GDL, electrical conductivity, permeability, and affects the pores. Carbon cloth based GDL withstands higher strain level when compared to carbon paper and the pore structure is also disrupted to a greater extent in cloth based GDL. In the present paper, we have addressed the effects of stress on pore structure of cloth based GDL. An optimum GDL must offer low mass transport resistance in an operating PEM fuel cell. The pore size analysis of pristine GDL and GDLs pressed at different pressure levels (200, 600 & 1000 kg cm−2) and their characteristics are evaluated using capillary flow porometry. The compressive stress affects the three types of pores in GDL called bubble point pore, mean flow pore and smallest pore. The change in electrical resistance, wetting behavior and surface morphology is also examined as a function of compressive stress. The fuel cell performances using these GDLs pressed at different compressive stresses are also evaluated and presented. The highest PEMFC performance is achieved at a compressive stress of 200 kg cm−2, which could be attributed to the combined effect of reduced ohmic resistance and optimized pore structure. The order of increasing performance in terms of current density is observed to be j200 > jPristine > j600 > j1000 at 0.15 V. The thicknesses and pore sizes of custom made GDL for optimum fuel cell performance are recommended.