Nanofiber network ion-exchange membranes for PEM fuel cells

An entirely new approach for fabricating proton conducting fuel cell membranes, based on the forced assembly of ionomeric and uncharged polymers, has been developed. An electrospun mat of proton-conducting polymeric nanofibers is created and then intersecting fibers are welded to produce a three-dimensional nanofiber network. An inert/impermeable (uncharged) polymer is impregnated into the void space between the fibers to provide mechanical strength, gas barrier properties, and controlled water swelling. Thus, the role of the mechanical support polymer is decoupled from that of the proton conducting material. In the present study, the nanofiber network (occupying about 70% of the dry membrane volume) was composed of sulfonated poly(arylene ether sulfone) with an ion-exchange capacity of 2.1-2.6 mmol/g. To further enhance proton conductivity, the nanofibers were electrospun from a polymer solution containing 35 or 40 wt% sulfonated polyhedral oligomeric silsesquioxane. Norland Optical Adhesive (NOA) 63, a UV-curable pre-polymer, was embedded into the sulfonated polysulfone mat. The resulting films were gas impermeable, with a proton conductivity greater than that for DuPont's Nafion at temperatures ranging from 30 to 120°C and relative humidities of 60-95%.