Artificially designed, low humidifying organic–inorganic (SFBC-50/FSiO2) composite membrane for electrolyte applications of fuel cells

The composite membranes composed of sulfonated fluorinated block copolymer (SFBC-50) having the degree of sulfonation (DS) of 50% and 3, 6, 9, 12 or 15 wt% functionalized silica (FSiO2) were prepared by facile solution casting method. SFBC-50 was synthesized via nucleophilic substitution polymerization reaction, where the hydrophilic units are di-sulfonated poly arylene ether sulfone and the hydrophobic units are fluorinated polyarylene perfluoropropane biphenyl. The simple, but effective functionalization of SiO2 is performed by fuming chlorosulfonic acid in order to increase the per unit volume of sulfonate (-SO3H) groups on SiO2 surface. The ability of FSiO2 particles afforded an unprecedented approach to simultaneously tune up the physio-chemical properties and mechanical strength of the composite membrane, which are evidenced by the results of water uptake measurement and dynamic mechanical analysis (DMA). Several characterization techniques, include FE-SEM, AFM, 1H-NMR, FT-IR, DSC, XRD and UTM, DMA, were exploited in order to gain insights on the morphology, chemical structure, intermolecular bond stretching, glass transition temperature, crystallinity and mechanical properties of the samples. The proton conductivity of pristine SFBC-50 membrane at 90 °C under 40% relative humidity (RH) is 6.9 mS/cm, which is lower by 1.91 times than that of membrane containing 12 wt% of FSiO2 (13.2 mS/cm). In contrast, under identical operating conditions, the Nafion-117 membrane showed the conductivity of 8.1 mS/cm, a 1.6 fold lower conductivity compared to that of the prepared composite membrane. Furthermore, the composite membrane revealed a much lower H2 gas permeability than those of pristine SFBC-50 and Nafion-117 membrane.