Proton-conducting nanocomposite membranes based on P(VDF-co-CTFE)-g-PSSA graft copolymer and TiO2–PSSA nanoparticles

Bifunctional TiO2 nanoparticles with hygroscopic and proton-conductive properties were synthesized by grafting proton-conducting polymer, i.e. poly(styrene sulfonic acid) (PSSA) from TiO2 nanoparitlces via surface-initiated atom transfer radical polymerization (ATRP). These bifunctional TiO2–PSSA nanoparticles were blended with poly(vinylidene fluoride-co-chlorotrifluoroethylene)-graft-poly(styrene sulfonic acid), i.e. P(VDF-co-CTFE)-g-PSSA to give proton-conducting membranes for high temperature fuel cells. FT-IR, UV–visible spectroscopy and X-ray diffraction (XRD) results revealed bifunctional properties of TiO2–PSSA nanoparticles due to successful grafting of PSSA chains. Ion exchange capacity (IEC) of P(VDF-co-CTFE)-g-PSSA/TiO2–PSSA membranes was not significantly changed irrespective of TiO2–PSSA concentrations, representing almost fixed SO3− concentration in the membranes. In contrast, water uptake and proton conductivity of membranes continuously increased with increasing TiO2–PSSA concentrations, presumably due to hygroscopic, soft conducting property of nanoparticles. The results of thermal gravimetric analysis (TGA) also showed that all the membranes were stable at least up to 280 °C.