Long-side-chain type imidazolium-functionalized fluoro-methyl poly(arylene ether ketone) anion exchange membranes with superior electrodialysis performance

Abstract

Developing highly ion conductive and desirable electrodialysis (ED) performance anion exchange membranes (AEMs) is of great significance. In this work, we report a strategy for fabricating novel AEMs based on a series of fluoro-methyl poly(arylene ether ketone)s having long-side-chain imidazolium groups for ED. Having hydrophilic conductive flexible side-chain imidazolium groups and rigid hydrophobic backbone within AEM matrix, the optimized AEM (PAEK-60-im) shows low water uptake of 24.9% at 80 °C and desirable ion conductivity of 22.01 mS cm–1 at 30 °C. In NaCl removal application of ED, PAEK-60-im shows the NaCl removal ratio of 69.66% within 120 min, outperforming commercial AEM-Type II (68.98%). Accordingly, it has a higher current efficiency of 83.7% but lower energy consumption of 5.9 kWh kg–1, compared with the commercial one (82.0%; 6.6 kWh kg–1). In particular, in selectrodialysis application, possibly owing to the synergistic effect of pore-size sieving effect resulting from macro-separation morphology and hydration energy difference of SO42– ions (–1000 kJ mol–1) and Cl– ions (–317 kJ mol–1) in feeding solution, PAEK-60-im shows significantly superior monovalent anion perm-selectivity (Cl−/SO42−) of 7.70 at 30 min, relative to commercial anion-selective Neosepta ACS (5.27) and many other reported mono-valent anion selective AEMs having elegant surface modified layers. The superior ED performance of the homogeneous PAEK-60-im is suggestive of its potential separation application.