Nafion-bifunctional silica composite proton conductive membranes

Sol-gel derived sulfonated phenethylsilica with hydrophilic -Si-OH and proton conductive -SO3H functional groups was used as a bifunctional additive to improve the proton conductivity and water uptake characteristics of Nafion. Nafion-bifunctional silica (NBS) composite membranes were prepared by casting Nafion-ethanol solutions mixed with sulfonated phenethylsilica sol. The ion exchange capability of NBS composite membranes increases linearly with the amount of bifunctional silica incorporated, and is about 1.9 x 10(-3) mol SO3H g(-1) for NBS with 7.5 wt% silica. Liquid water uptake measurements showed that NBS composite membranes have higher water uptake (g H2O g(-1) composite membrane) than bare recast Nafion while the degree of hydration (i.e., nH(2)O-SO3H) remains fairly constant. The NBS composite membranes showed improved proton conductivity when compared with bare recast Nafion and Nafion 117 membranes at 80 degreesC and over a range of relative humidity.