Promotion of anhydrous proton conduction by polyvinyl alcohol in liquid crystalline composite membranes containing 1-tetradecyl-3-methylimidazolium hydrogen sulfate

摘要

Composite membranes composed of liquid crystalline 1-tetradecyl-3-methylimidazolium hydrogen sulfate and polyvinyl alcohol are prepared for anhydrous proton conduction. The composite membranes exhibit smectic A liquid crystal phase in which polyvinyl alcohol chains aggregate into lamellas between the bilayers formed by the alkyl imidazolium hydrogen sulfate. Smectic order of hydrogen sulfate anions ensures formation of hydrogen-bonded chains for proton conduction via a hopping mechanism. Electrochemical measurements reveal that temperature-dependent ionic conductivity of the composite membranes approximately follows an Arrhenius-type law and reaches 20.5 mS cm(-1) at 140 degrees C, which is twice that of the pure ionic liquid crystal. Potentiostatic polarization measurements show that proton transfer number of the composite membrane is also promoted. Polyvinyl alcohol promotes anhydrous proton conduction by constructing additional hybrid hydrogen-bonded chains consisting of hydroxyl groups of PVA and hydrogen sulfate anions. The ionic liquid crystalline composite membranes possess the potential application in intermediate temperature fuel cells.