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.

Efficiency and Oxidation Performance of Densely Flexible Side-Chain Piperidinium-Functionalized Anion Exchange Membranes for Vanadium Redox Flow Batteries

“…The properties of AEMs are closely influenced by some structural factors, including the types of cationic groups, the linking ways of cations with polymer backbone, and their aggregation distribution in structural units. ,− In the previous study of high-performance AEMs, we designed and reported a class of AEMs containing eight flexible piperidine ions based on poly­(aryl ether sulfone)­s . It is found that the combination of densely flexible side chains and piperidinium ions in the hydrophilic structural units of AEMs is very effective to improve their hydroxyl conductivity and alkaline stability.…”

Progress in High‐Performance Anion Exchange Membranes Based on the Design of Stable Cations for Alkaline Fuel Cells

“…The properties of AEMs have a close relationship with polymer structures, [32,33] including the category and structure of cationic group, the composition and spatial structure of the polymer backbone and the type of linkage between the ionic group and polymer backbone. [34][35][36] Among these factors, the structure of cationic group is one of the key factor to be considered next to the polymer backbone, which has a profound impact on the alkaline resistance stability and hydroxide conductivity of AEMs. Quaternary ammonium (QA) cations are the most studied functional cations for AEMs in the past several years because of their convenience, maturity and ease, and low cost of the synthesis process.…”

Molecular dynamics study on water and hydroxide transfer mechanisms in PSU-g-alkyl-TMA membranes at low hydration: Effect of side chain length

“…The hydrophobicity of the long chain tends to form more efficient hydrophilic phase topology and to increase the anionic conductivity and/or chemical stability of the ammonium group [8,17,19,34e42]. In the case of the QA group, the graft (also named side chain) can be tuned by increasing the length of the intermediate alkyl chain (spacer unit) or by substituting one of the methyl group for a longer chain (extender chain) [17,18,37,39,43,45]. Coarse grained MD with a PPO (polyphenylene oxide) backbone show that hydrophilic morphology can be designed by the pattern of the tethering from the lamellar structure to a more interconnected one [46,47].…”