In situ sol–gel route to novel sulfonated polyimideSiO 2 hybrid proton‐exchange membranes for direct methanol fuel cells

Polyimides (PIs) as high‐performance organic matrices are used in the preparation of PI composites because of their excellent mechanical, thermal and dielectric properties. The sol–gel method is a promising technique for preparing these PI composites due to the mild reaction conditions and the process being controllable. Although sulfonated polyimide (SPI) proton‐exchange membranes have attracted much attention recently, studies on preparing SPI‐based hybrid proton‐exchange membranes for fuel cells have been rare. A series of SPISiO 2 hybrid proton‐exchange membranes were prepared from amino‐terminated SPI pre‐polymers, 3‐glycidoxypropyltrimethoxysilane (KH‐560) and tetraethylorthosilicate through a co‐hydrolysis and condensation process using an in situ sol–gel method. The reactive silane KH‐560 was used to react with amino‐terminated SPI to form silane‐capped SPI in order to improve the compatibility between the polymer matrix and the inorganic SiO 2 phase. The microstructure and mechanical, thermal and proton conduction properties were studied in detail. The hybrid membranes were highly uniform without phase separation up to 30 wt% SiO 2 . The storage modulus and tensile strength of the hybrid membranes increased with increasing SiO 2 content. The introduction of SiO 2 improved the methanol resistance while retaining good proton conductivity. The hybrid membrane with 30 wt% SiO 2 exhibited a proton conductivity of 10.57 mS cm −1 at 80 °C and methanol permeability of 2.3 × 10 −6 cm 2 s −1 possibly because the crosslinking structure and SiO 2 phases formed in the hybrids could retain water and were helpful to proton transport. Copyright © 2010 Society of Chemical Industry