Innovative Gas Diffusion Media for PEM Fuel Cells Based on a Fluorinated Polyurethane as Hydrophobic Agent

Abstract

The present work focuses on the use of an alternative polymer (Fluorolink® P56, a commercially available, anionic, segmented polyfluorourethane with high molecular weight) to be used as hydrophobic agent in GDMs production for PEMFCs. Prepared samples were physically evaluated by static contact angle, SEM analysis, porosimetry and finally tested in a single lab-scale fuel cell in order to assess electrochemical performances. In a typical experiment, carbon black (CB), Fluorolink P56 (two different concentrations) and isopropyl alcohol were mixed at 8000 rpm by using an Ultra Turrax homogeneizator. Inks produced were blade coated on hydrophobized commercial GDLs (SAATI Group). Then the samples were treated for 30 minutes at 150 °C in order to remove the wetting medium and to make the polymer fibrous. The layers based on Fluorolink P56 showed good surface uniformity and a superhydrophobic behavior (i.e. mean contact angle higher than 150°). Electrochemical tests, performed at 60 °C and 80 °C and low (60%) and high (100%) relative humidities, demonstrated that innovative GDMs are able to guarantee higher power density values in certain operating conditions and very low overall ohmic resistances, even though some critical issues still remain in diffusion limitations at high current densities, when more water is generated.