Electron-Donating C-NH2 Link Backbone for Highly Alkaline and Mechanical Stable Anion Exchange Membranes.

Abstract

Aryl-ether cleavage and benzylic quaternary ammonium (QA) group degradation are promoted by C═O groups in most commercial anion exchange membrane materials. Herein, a novel strategy of converting C═O groups to the electron-donating C-NH2 linkages in conventional poly(arylene ether ketone)s is proposed by reductive amination via Leuckart reaction. Density functional theory (DFT) calculations indicate that the model compound containing C-NH2 linkage exhibits much higher barrier heights for aryl-ether cleavage and QA group degradation by enhancing the electronic cloud density on both the ether-connected carbon and the benzylic carbon. The C-NH2 linkages also induce hydrogen bond networks in the membranes, which enhance intermolecular interaction and provide additional hydroxide transport sites. As a result, the C-NH2 linkage membranes exhibit excellent hydroxide conductivity (108.2 mS cm-1 at 80 °C) and tensile strength (48.4 MPa) with high elongation at break (50.8%). The C-NH2 linkage membranes also show outstanding alkaline stability with no detectable backbone degradation even in 4 M KOH at 80 °C for 400 h, which is at the top-level among the state-of-the-art main chain architecture AEMs. This study proposes a new strategy for the synthesis of highly stable AEMs based on electron-donating C-NH2 link backbone.