Anion exchange membranes with eight flexible side-chain cations for improved conductivity and alkaline stability

Abstract

Increasing the local charge density of flexible side-chain cations in the hydrophilic segments of anion exchange membranes (AEMs) is helpful for improving their properties. However, due to limitations of structural design strategies and available synthetic methods, very few AEMs with more than four flexible side-chain cationic groups in hydrophilic segments have been reported. In order to further improve the hydroxide conductivity, alkaline stability and dimensional stability, herein we report a series of AEMs containing eight flexible side-chain cations in hydrophilic segments, based on poly(aryl ether sulfone)s (PAES). The synthesis, ion exchange capacity (IEC), water absorption, dimensional swelling, alkaline stability and hydroxide conductivity of the obtained membranes (PAES-8TMA-x) were examined and the relationships between structures and properties of different types of AEMs were also systematically compared. The resulting AEMs with IEC values of 1.76–2.76 mmol g−1 displayed comprehensively desirable properties, with hydroxide conductivities of 62.7–92.8 mS cm−1 and dimensional swelling in the range of 8.3% to 15.8% at 60°C. The IEC and hydroxide conductivity for a representative sample, PAES-8TMA-0.35, maintained 82.2% and 79.6% of the initial values after being immersed in 2 mol L−1 NaOH at 90°C for 480 h, respectively. This study expands the design and preparation of AEMs containing high local densities of flexible side chain cations, and provides a new strategy for new AEM materials.