Effect of Different Hydrophobic Agents onto the Surface of Gas Diffusion Layers for PEM-FC

Abstract

In the present work two different hydrophobic agents (i.e. a Perfluoropolyether derivative, PFPE, and a Polytetrafluoroethylene, PTFE) were used to treat the surface of a carbon cloth gas diffusion layer (GDL) . Commercially available products were used in both cases, namely Fluorolink® P56 (supplied by Solvay Solexis s.p.a., Italy) for PPFE and Algoflon® D 1214X (supplied by Solvay Solexis s.p.a., Italy) for PTFE. The behaviour of the PFPE-based hydrophobic coating was compared with that of a standard PTFE one. The properties of a GDL coated with about 1 % wt of PFPE were analysed and compared with those of a 10 % wt PTFE coated GDL. Wettability of the PFPE- and PTFE-based surfaces were analysed by means of contact angle measurement. A simplified axisymmetric drop shape analysis technique was used on sessile drops. Static contact angles and contact angle hysteresis were evaluated at ambient temperature, at 60 °C and at 80 °C. Drop evaporation at the three temperatures was also evaluated. Both the surfaces were found to be highly hydrophobic. The obtained GDLs were used in a single fuel cell and tested in a lab scale. The cell testing was run at two temperatures (60 °C and 80 °C) with a relative humidity (RH) of the feeding gases of 80/100 %, Hydrogen/Air, respectively. The new PFPE coating sensibly improved the cell performances, and this effect was more evident at 60 °C than 80 °C.