Pendent persubstituted imidazolium and a polyimidazolium cross-linked polymer as robust alkaline anion exchange membranes for solid-state Zn-Air batteries

Abstract

Alkaline anion exchange membranes (AEMs) were developed from a series of persubstituted imidazolium cations with varying alkyl chains (Im-nC, nC = (CH2)n−1CH3; n = 4, 12, and 16) tethered on poly(vinylbenzyl chloride-co-acrylonitrile) (PVC-co-AN) to prepare a comb-shaped polymer membrane (M1-nC) and a cross-linked polymer membrane from polyimidazolium cations and PVC-co-AN (M3). The PVC-co-AN polymer backbone shows high stability after curing, and the water uptake and swelling ratio are controlled by varying the alkyl chain length in M1-nC even with temperature variation. Results show that M1-16C retains the highest ion exchange capacity (IEC) of 95% among the M1-nC series of membranes after exposure to 1 M KOH solution at 80 °C for 30 days. However, the longer alkyl chains hindered the interconnected ion channels limiting the hydrophobic/hydrophilic phase separation and the hydroxide ion conductivity. Meanwhile, M3 exhibits a distinct microphase-separated morphology and a high ionic conductivity of 54.5 mS/cm for a 2.02 IEC with high stability to retain an IEC of 97% after storage in 1 M KOH solution at 80 °C for 30 days. In addition, all the AEMs exhibit high oxidation stability and retain >96% weight after immersion into 4 ppm Fenton’s reagent at 80 °C. Moreover, the flexible solid-state zinc–air batteries comprising an M3 membrane displayed a peak power density of 165 mW cm–2 and superior cycling stability (30 h at 10 mA cm–2) demonstrating very promising applications in solid-state flexible rechargeable Zn–air batteries.