New organic-inorganic hybrid membranes based on sulfonated polyimide/aminopropyltriethoxysilane doping with sulfonated mesoporous silica for direct methanol fuel cells

A series of novel composite methanol-blocking polymer electrolyte membranes based on sulfonated polyimide (SPI) and aminopropyltriethoxysilane (APTES) doping with sulfonated mesoporous silica (S-mSiO2) were prepared by the casting procedure. The microstructure and properties of the resulting hybrid membranes were extensively characterized. The crosslinking networks of amino silica phase together with sulfonated mesoporous silica improved the thermal stability of the hybrid membranes to a certain extent in the second decomposition temperature (250400 degrees C). The composite membranes doping with sulfonated mesoporous silica (SPI/APTES/S-mSiO2) displayed superior comprehensive performance to the SPI and SPI/APTES membranes, in which the homogeneously embedded S-mSiO2 provided new pathways for proton conduction, rendered more tortuous pathways as well as greater resistance for methanol crossover. The hybrid membrane with 3 wt % S-mSiO2 into SPI/APTES-4 (SPI/A-4) exhibited the methanol permeability of 4.68 x 10-6 cm2 s-1at 25 degrees C and proton conductivity of 0.184 S cm-1 at 80 degrees C and 100%RH, while SPI/A-4 membrane had the methanol permeability of 5.16 x 10-6 cm2 s-1 at 25 degrees C and proton conductivity of 0.172 S cm-1 at 80 degrees C and 100%RH and Nafion 117 exhibited the values of 8.80 x 10-6 cm2 s-1 and 0.176 S cm-1 in the same test conditions, respectively. The hybrid membranes were stable up to about 80 degrees C and demonstrated a higher ratio of proton conductivity to methanol permeability than that of Nafion117. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012