Preparation of anion exchange membrane with enhanced conductivity and alkaline stability by incorporating ionic liquid modified carbon nanotubes

An effective strategy to improve both the conductivity and alkaline stability of anion exchange membranes (AEMs) was proposed by incorporating imidazolium ionic liquids (ImILs) modified 1D carbon nanotubes (IL@CNT) into imidazolium-based poly (ether ether ketone) (ImPEEK). Two types of ionic liquids (IL-M and IL-B) with different alkaline stability were chemically attached to CNTs. The introduction of IL@CNT provided the hybrid membranes with additional ion hopping positions and 1D long-range ion-conducting channels. The ImPEEK/IL-B@CNT-6 membrane with a high ion exchange capacity (IEC) of 2.49 mmol g−1 possessed the hydroxide conductivity of 134.52 mS cm−1 (70 °C, 100% RH) which was 1.7 times that of the pure ImPEEK membrane (80.20 mS cm−1). Meanwhile, the hybrid membranes showed enhanced alkaline stability due to the steric hindrance offered by CNTs and good alkaline resistance of IL-B with more bulky substituents. The residual ratio of hydroxide conductivity of ImPEEK/IL-B@CNT-8 after being treated in 2 M KOH at 50 °C for 48 h reached 77.47% (54.37% for pure ImPEEK and 70.21% for ImPEEK/ILM@CNT-8). The theoretical calculations of LUMO energy for IL-M (−1.83 eV) and IL-B (−1.74 eV) were in good accordance with experimental results. The ImPEEK/IL-B@CNT-6 hybrid membrane presented an improved fuel cell performance with the peak power density of 80.59 mW cm−2 at 50 °C which was 1.6 times that of the pure ImPEEK membrane. Mechanical properties, dimensional and thermal stability of the as-prepared hybrid membranes were also enhanced due to the improved interface compatibility.