Functionally graded nano-porous gas diffusion layer for proton exchange membrane fuel cells under low relative humidity conditions

Gas diffusion layers (GDLs) were fabricated using commercially available carbon paper as macro-porous layer substrate. Functionally graded nano-porous layers were designed by combining carbon nano-fibers with nano-chain type Pureblack carbon (75:25–0:100 wt.%) in the z-direction towards the catalyst layer and Teflon content (say 15–30 wt.%) to obtain variation in pore diameter and also hydrohobicity. On the top of the nano-porous layer, a thin layer of hydrophilic inorganic oxide (fumed silica) was also deposited to retain moisture content to maintain the electrolyte wet, especially when the fuel cell is working at lower relative humidity (RH) conditions, which is typical for automotive applications. The surface morphology, contact angle, bulk characteristics and pore size distribution of the layered GDLs were examined using FESEM, Goniometer, Interferometer and Hg Porosimeter, respectively. The GDLs assembled into MEAs were evaluated in single cell PEMFC under various operating conditions (temperature and RH) using H2/O2 and H2/air as reactants. It was observed that the functionally graded nano-porous GDLs with hydrophilic layer showed an excellent fuel cell performance with a peak power density of about 0.46 W/cm2 at 85 °C using H2 and air at 50% RH.