Novel anion exchange membrane with poly ionic liquid-confined hypercrosslinked polymer for enhanced anion conduction and stability

Abstract

Hypercrosslinked polymer (HCP) holds great potential for utilization as novel anion exchange membrane (AEM) material due to their rich microporous structure and high thermal/chemical stability while remaining challenges due to lack of hydroxide carriers. Herein we report a novel strategy of fabricating poly ionic liquid (PIL)-confined HCP for ion transfer. PIL precursors are loaded into the pores of HCP and in-situ polymerized to prepare PIL@HCP, which is then incorporated into quaternized poly (2,6-dimethyl-1,4-phenylene oxide) (QAPPO) to fabricate composite membrane. The introduction of PIL provides high concentration of quaternary ammonium (QA) groups in the porous networks of HCP. And the organic components impart outstanding compatibility between PIL@HCP and QAPPO matrix. All these permit the formation of interconnected hydroxide transfer channels through the membranes. Especially, the rigid and hydrophobic HCP functions with steric hindrance effectively impedes the attack of hydroxide ions on QA groups and maintains structure stability. Accordingly, the PIL@HCP/QAPPO composite membrane with high ion exchange capacity (IEC) of 2.33 mmol g−1 achieves a hydroxide conductivity of 98 mS cm−1 (80 °C, 100% RH), 92% higher than that of QAPPO. Meanwhile, the area swelling degree of PIL@HCP/QAPPO reduces to 13.6% in comparison to QAPPO (25.7%) and its conductivity retains 88% after alkaline treatment.