The development of anion exchange membranes (AEMs) is hindered by the trade-off of ionic conductivity, alkaline stability, and mechanical properties. Tröger’s base polymers (Tb-polymers) are recognized as promising membrane materials to overcome these obstacles. Herein, the AEMs made from Tb-poly­(crown ether)­s (Tb-PCEs) show good comprehensive performance. The influence of crown ether on the conductivity and alkaline stability of AEMs has been investigated in detail. The formation of hydronium ion-crown ether complexes and an obvious microphase-separated structure formed by the existence of crown ether can enhance the conductivity of the AEMs. The maximum OH– conductivity of 141.5 mS cm–1 is achieved from the Tb-PCEs based AEM (Tb-PCE-1) at 80 °C in ultrapure water. The ion-dipole interaction of the Na+ with crown ether can protect the quaternary ammonium from the attack of OH– to improve the alkaline stability of AEMs. After 675 h of alkaline treatment, the OH– conductivity of Tb-PCE-1 decreases by only 6%. The Tb-PCE-1-based single cell shows a peak power density of 0.202 W cm–2 at 80 °C. The prominent physicochemical properties are attributed to the well-developed microstructure of the Tb-PCEs, as revealed by TEM, AFM, and SAXS observations.

In recent years, with the continuous application of superacid-catalyzed condensation reaction in the preparation of anion exchange membranes (AEMs), a number of AEMs with excellent performance have been designed. Among them, the method to copolymerize two aromatic compounds with piperidone via a superacid-catalyzed reaction to synthesize anionic conducting copolymers has been widely discussed by researchers. Here, we focus on the introduction of poly­(N-alkylcarbazole-co-terphenyl N,N′-dimethylpiperidinium) (PCTP-n), which is formed by copolymerizing different chain lengths of N-alkylcarbazole (AHC, n = 2, 4, and 6) and p-terphenyl with 1-methyl-4-piperidone (1M4P). As a result of the high-curvature backbone and hydrophobic flexible side chains, the PCTP-n AEMs show comprehensive performance advantage. Among them, the PCTP-6 membrane, with an ultralow swelling (7.9%) and an excellent OH– conductivity retention (91.9% in 2 M NaOH at 80 °C after 1080 h), highlights high dimensional stability and alkaline resistance. Then, the PCTP-2 membrane displays excellent mechanical robustness (EB: 40%, TS: 20 MPa) and a decent OH– conductivity (134 mS cm–1 at 80 °C). Furthermore, the PCTP-2-based single cell exhibits a decent power density of 542 mW cm–2 under H2–O2 condition.

The application of anion exchange membranes (AEMs) in alkaline fuel cells is profoundly affected by its performance. In this work, Tröger’s base microporous AEMs with hyperbranched structure (QA-BTB-x%) are prepared by superacid catalysis. The introduction of the hyperbranched structure can enhance the free volume of the AEMs, which will improve the water uptake (WU) of the AEMs and thus promote the transport of OH–. By increasing the content of the branching agent from 0% to 8%, the WU of the AEMs gradually increased from 41.7% to 62.6% at 80 °C. The maximum OH– conductivity of the QA-BTB-5% AEMs can reach to 95.2 mS cm–1 in ultrapure water at 80 °C with a low swelling ratio (14.9% at 80 °C). Small angle X-ray scattering (SAXS), atomic force microscopy (AFM) and transmission electron microscopy (TEM) show that the QA-BTB-5% AEMs has a good microphase separation structure that is beneficial for OH– transport. After a long-term alkaline stability test, the QA-BTB-5% still has a high OH– conductivity. The maximum power density of the QA-BTB-5%-based single cell can reach to 548 mW cm–2 in H2/O2. All of the results demonstrate obvious performance enhancements of AEMs upon the introduction of hyperbranched structure into the polymer backbone.

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