Structure and Properties of New sPEEK/Zirconia/Protic Ionic Liquid Membranes for Fuel Cell Application

Hybrid organic-inorganic membranes based on sulfonated poly(ether ether ketone) (sPEEK), zirconium oxide, and the protic ionic liquid (PIL) diethylmethylamine triflate ([dema][TfOH]) have been synthesized. Their structure has been investigated by X-ray diffraction and small-angle X-ray scattering and correlated to their electrical and thermomechanical properties. The membranes present good mechanical and chemical stabilities, as well as thermal stability over 300 degrees C. Zirconia contents up to 5 wt% (10 wt% PIL) lead to the formation of isolated zirconia-rich aggregates dispersed in the polymer matrix, constituted of spatially correlated zirconia nanoparticles. This segregation of zirconia species in nanodomains, interacting with sulfonic groups of sPEEK, inhibits conductivity. Differently, zirconia content of 6 wt% (10 wt% PIL) induces a conductivity much higher than pristine sPEEK, due to the formation of an extended fractal structure in the whole sample, constituted of connected zirconia-rich aggregates. Interaction of PIL molecules with the zirconia aggregates along this extended structure shall form new conducting channels for ion transport, favoring conductivity.