Lamellar Lyotropic Liquid Crystal Superior to Micellar Solution for Proton Conduction in an Aqueous Solution of 1-Tetradecyl-3-methylimidazolium Hydrogen Sulfate.

Humidified perfluorosulfonic acid polymers with a nanoscopic phase-separated morphology are highly proton-conductive materials for fuel cells, yet morphology tuning of the acidic materials for enhanced conduction remains a challenge. Aqueous acidic lyotropic liquid crystals (LLCs) provide a powerful platform to construct well-defined nanostructures for proton conduction. We report an aqueous LLC formed by 1-tetradecyl-3-methylimidazolium hydrogen sulfate, exhibiting a proton conductivity of 210 mS cm at 25 °C, which surpasses that formed by alkylsulfonic acid, thus demonstrating that a mobile acidic anion is more efficient than constrained sulfonic acid functionality to transport protons in LLCs. For an aqueous solution of 1-alkyl-3-methylimidazolium hydrogen sulfate, a lamellar LLC results in higher conductivity than a micellar solution under the same hydration conditions. The peak power density of the fuel cell fabricated from porous membranes filled with the lamellar LLC is four times as high as that filled with the micellar solution. The work offers an efficient way to construct highly proton-conductive LLC materials for fuel cell application.