Characterization of sulfonated poly(arylene ether sulfone) (SPAES)/silica-phosphate sol-gel composite membrane: Effects of the sol-gel composition

Abstract

Proton-conducting composite membranes were prepared from sulfonated poly(arylene ether sulfone) (SPAES) and silica-phosphate sol-gel by using a solution casting method. The silica and phosphate precursors of tetraethylorthosilicate (TEOS) and triethyl phosphate (TEP), and the sol-gel network formation of silica-phosphate, were confirmed using Fourier transform infrared (FTIR) spectroscopy. Increases in water affinity by incorporating silica-phosphate were observed in all composite membranes, which also resulted in higher ion-exchange capacity than with pure SPAES. The water desorption behavior of the SPAES composite membranes was determined by the weight loss at 80 °C using thermogravimetric analysis (TGA). The SPAES/7S3P (7 and 3 indicate the added molar ratio of silica and phosphate, respectively) composite membrane showed the strongest water retention capacity. As the temperature increased in fully hydrated conditions, all membranes exhibited increasing proton conductivity due to enhanced proton mobility. The proton conductivity at low humidity depended on the water retention capacity, indicating that the incorporation of silica-phosphate was effective in enhancing the proton conductivity through the hopping transfer. The best performance was obtained in the SPAES/7S3P composite membrane, showing a conductivity of 29.6 mS/cm at 120 °C with 40% relative humidity, which is twice to that of Nafion 112 (14.6 mS/cm).