Properties and Fuel Cell Performance of a Nanofiber Composite Membrane with 660 Equivalent Weight Perfluorosulfonic Acid

A nanofiber composite membrane, composed of 72 vol% 660 equivalent weight (EW) perfluorosulfonic acid (PFSA, from 3 M Company) and 28 vol% polyphenylsulfone (PPSU), was fabricated and characterized. A newly developed dual fiber electrospinning method was utilized for membrane fabrication, where the two polymers were simultaneously electrospun into a single mat. Follow-on processing converted the mat into a fully dense and functional fuel cell ion-exchange membrane with polyphenylsulfone nanofibers embedded in the ionomer. The proton conductivity of the composite membrane was high, e.g., 93 mS/cm at 120°C, 50% relative humidity, compared to 37 mS/cm for commercial Nafion. The dimensional stability of the membrane upon liquid water uptake was excellent, with an in-plane (areal) swelling of only 5% at room temperature. A MEA containing a 660 EW nanofiber composite membrane with 3 M 825 EW PFSA ionomer as the catalyst binder had significantly higher power output in a hydrogen/air fuel cell than a MEA with a Nafion 211 membrane and Nafion PFSA binder. The power output of the nanofiber membrane MEA was relatively insensitive to changes in feed gas humidity, between 50% and 93% RH for cell temperatures of 80°C and 100°C.