Novel self-cross-linked multi-imidazolium cations long flexible side chains triblock copolymer anion exchange membrane based on ROMP-type polybenzonorbornadiene

Abstract

A novel benzonorbornadiene derivative (BenzoNBD-Bis(Im+Br−-Im+I−)) grafted by multi-imidazolium cations side-chains combined the rigid alkyl spacer and flexible alkoxy spacer is designed and synthesized. Then, the BenzoNBD-Bis(Im+Br−-Im+I−) monomer is copolymerized with the epoxy functionalized norbornene monomer (NB-MGE) and norbornene (NB) via ring-opening metathesis polymerization (ROMP) using Grubbs 3rd catalyst. All as-designed triblock copolymer membranes (TBCMs) show a thermal decomposition temperature beyond 310 °C and can well be dissolved in common organic solvents. The self-cross-linked structure of anion exchange membrane (AEM) is confirmed by gel fraction and tensile measurement. The water uptake and swelling ratio of TBCMs and AEMs are also measured. Major properties required for AEMs such as ion exchange capacity (IEC), hydroxide conductivity and alkaline stability are investigated. AEM-9.09 shows a hydroxide conductivity of 100.74 mS cm−1 at 80 °C. Besides, the micro-phase separated morphology of AEM is confirmed by TEM, AFM and SAXS analyses, AEMs formed distinct micro-phase separation. The as-prepared AEM exhibits a peak power density of 174.5 mW cm−2 at 365.1 mA cm−2 tested in a H2/O2 single-cell anion exchange membrane fuel cell (AEMFC) at 60 °C. The newly developed strategy of self-cross-linked multi-imidazolium cations long side-chains triblock benzonorbornadiene copolymer provides an effective method to develop high-performance AEMs.