Multiple Enhancement Effects of Crown Ether in Tröger's Base Polymers on the Performance of Anion Exchange Membranes.

Abstract

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.