Anisotropic polymer membranes retaining nanolayered hydrogen sulfate anions for enhanced anhydrous proton conduction

• Published in: Journal of membrane science 2022-10, Vol.662, p.120975, Article 120975
• Main Authors: Luo, Jie, Yang, Qing, Tan, Shuai, Wang, Caihong, Wu, Yong
• Format: Article
• Language: English
• Subjects: Imidazolium hydrogen sulfate; Liquid crystal; Membrane; Nanolayer; Proton conduction
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/j.memsci.2022.120975

Ionic liquids bearing acidic anions are intrinsically proton-conductive but mechanically weak for device application. Maintaining ionic conductivities after solidifying ionic liquids by polymerization remains a challenge due to the restriction of ion mobility. In this work, nanolayered ionic membranes bearing aligned acidic hydrogen sulfate anions are prepared from ionic liquid crystals for enhanced anhydrous proton conduction. To obtain polymerizable smectic assemblies, 3-tetradecyl-1-vinyl-imidazolium hydrogen sulfate as monomer and 3, 3'-(decane-1,10-diyl) bis(1-vinyl-imidazolium) hydrogen sulfate as cross-linker are synthesized. In situ polymerization of the ionic assemblies in the smectic phase results in robust membranes retaining nanolayered acidic anions. The nanolayered ionic membranes exhibit tensile strengths up to 16.6 MPa and keep thermally stable at temperatures up to 220 °C. Anhydrous conductivity of the aligned ionic membrane reaches a maximum of 22 mS cm−1 and follows the Arrhenius law. A peak power density of 71.5 mW cm−2 is achieved at 110 °C for the fuel cell constructed from the nanolayered ionic membrane under non-humidified conditions. A nanolayered membrane was prepared by in situ polymerization of imidazolium hydrogen sulfate liquid crystalline self-assemblies. The layered anions enhanced proton conductivity of the membrane in a non-humidified fuel cell. [Display omitted] •Liquid crystalline imidazolium hydrogen sulfate monomer/crosslinker are prepared.•Robust nanolayered membranes are polymerized from the ionic liquid crystals.•Acidic anions aggregate into lamellas to achieve anhydrous proton conduction.•Macroscopic alignment of the membrane promotes power density of fuel cells.