Anisotropic behavior of mechanically extruded sulfonated polysulfone: Implications for proton exchange membrane fuel cell applications

Suflfonated polysulfone (sPSU) ionomer has recently emerged as very promising alternative to perfluorinated membranes in proton exchange membrane fuel cell applications. To elucidate the effect of membrane fabrication process on the final properties of the films, sPSU membranes were prepared by two of the most common preparation procedures, that are mechanical extrusion by doctor blade or recast process, and characterized for their morphological, mechanical, dimensional and transport features. A clear anisotropy was observed in the proton conductivity, dimensional swelling and mechanical resistance of mechanically oriented sPSU. Recast membrane exhibited higher through-plane conductivity and promises for better fuel cell performance. Contrariwise, mechanical extrusion process can fabricate membrane with superior mechanical strength and outstanding anti-swelling ability. The latter procedure could be exploited to prepare thin but still stable and strength sPSU membranes able to better perform in PEMFCs.