Hydrophobic Side-Chain Attached Polyarylether-Based Anion Exchange Membranes with Enhanced Alkaline Stability

Abstract

In order to improve the alkaline stability of polyarylether-based anion exchange membranes (AEMs), the strategy of attaching a hydrophobic side-chain to the backbone is proposed. A series of AEMs which include three original quaternary ammonia AEMs (QAPSF, QAPPSU, and QAPPO) and three hydrophobic side-chain attached AEMs (sQAPSF, sQAPPSU, and sQAPPO) are synthesized. Although a gradual enhancement of chemical stabilities for QAPSF, QAPPSU, and QAPPO is observed by reducing backbone polar groups, degradation of the original QA-type AEMs is still obvious. After testing in 1 M N2-saturated NaOH solution at 60 °C for 30 days, the weight losses of the original QA-type AEMs exceed 29%; the IEC losses of the AEMs exceed 24%, and the IC losses of the AEMs exceed 25% (IEC, ion exchange capacity). While for s-type AEMs, due to the hydrophobic side-chains endowing the membranes with hydrophilic/hydrophobic microphase separation morphologies, the backbones are protected from OH- attacking; significant improvements of the AEMs’ chemical stabilities are achieved. After the 30 day test, the side-chain attached AEMs exhibit much higher stabilities than those of original AEMs. The weight loss percentages for sQAPSF (IEC = 1.02 mmol g-1), sQAPPSU (IEC = 1.05 mmol g-1), and sQAPPO (IEC = 2.52 mmol g-1) are 8%, 8%, and 10%, respectively. The IECs of sQAPSF, sQAPPSU, and sQAPPO are reduced by 12%, 10%, and 15%, respectively. The ionic conductivities of the membranes are reduced by 15%, 12%, and 8%, respectively. Besides, compared to the original AEMs, the side-chain attached AEMs show enhanced ionic conductivity and suppressed swelling behavior. The results explicitly show that the approach of introducing a hydrophobic side-chain is an effective way to elevate the chemical stabilities of polyarylether-based AEMs.