Lyotropic ionic liquid crystal gels derived from polyimidazolium hydrogen sulfate for enhanced proton conductivity

Abstract

Anisotropic gels developed from polymer networks accommodating lyotropic liquid crystals are promising electrolytes but electrochemically inert polymers prevent ions from being conducted efficiently. In this work, we synthesized protic ionic liquid polymer in lyotropic ionic liquid crystal to improve proton conduction across the polymer skeleton in anisotropic gels. In situ polymerization of 1‐vinylimidazolium hydrogen sulfate ionic liquid dissolved in aqueous 1‐tetradecyl‐3‐methylimidazolium hydrogen sulfate lyotropic liquid crystal gave chemical liquid crystal gels exhibiting both dynamic order and mechanical strength. The protic ionic liquid polymer bridged the hydrogen bond chains between neighboring ionic lyotropic liquid crystal domains to give a proton conductivity of 117 mS cm−1 at 25°C. Macroscopic alignment of the liquid crystal gel achieved by mechanical shearing promoted proton conductivity to 137 mS cm−1. The macroscopically aligned liquid crystal gel acted stably in a fuel cell device, delivering a peak power density 2.95 times higher than the unaligned one. Gelation of lyotropic ionic liquid crystals with protic ionic liquid polymer provides an effective strategy to develop anisotropic gel electrolytes for electrochemical devices.