Proton-conducting membranes based on HTFSI-doped PEI/SiO2 nanocomposites

Novel proton-conducting membranes comprising polymer/inorganic materials based on linear polyethyleneimine (LPEI)/SiO2 nanocomposites synthesized through sol–gel processing have been prepared. 3-Glycidyloxypropyl-trimethoxysilane (GLYMO) has been used to cross-link the LPEI to afford improved heat resistance. The addition of trifluoromethanesulfonimide (HTFSI) during membrane processing doped the amine groups of LPEI to form immobilized Brønsted acid–base pairs, which provide the hybrid membrane's proton conductivity. The resulting membranes show a proton conductivity as high as 1 × 10−2 S/cm at 90 °C, 100% relative humidity and 5.6 × 10−5 S/cm at high temperatures (≥130 °C) under anhydrous conditions. The effects of temperature, humidity and mobility of active groups on the conductivity are discussed.