Sulfonated polysulfone/POSS nanofiber composite membranes for PEM fuel cells

A class of nanofiber-based polymer/particle proton exchange membranes (PEMs) is described for use in H₂ /air fuel cells that operate at low humidity. The membranes were fabricated from electrospun nanofibers composed of sulfonated poly(arylene ether sulfone) (sPAES) with sulfonated polyhedral oligomeric silsesquioxane (sPOSS) as a proton conductivity enhancer. The void space between nanofibers in an electrospun mat was filled with a mechanically robust and chemically stable UV-cross-linked polyurethane to create a gas impermeable membrane. Membranes with nanofibers composed of 2.1 mmol/g ion-exchange capacity sulfonated polysulfone with 40 wt % sPOSS and a nanofiber volume fraction of 0.70 exhibited a proton conductivity of 0.094 S/cm at 30°C and 80% relative humidity (RH), which was 2.4 times higher than that of Nafion 212 at the same conditions. The high proton conductivity was attributed to the high concentration of protogenic groups in the sPAES/sPOSS nanofibers and the ability of the nanofibers to hold water, where the equilibrium water-vapor uptake of the membrane was 3.8 times higher than that of commercial Nafion at 30°C and 80% RH.