High-Performance Anion Exchange Membranes with Para-Type Cations on Electron-Withdrawing C=O Links Free Backbone

As critical triggers, both the electron-withdrawing links and neighboring cationic groups induce and accelerate the aryl ether cleavage in the widely used aryl ether containing anion exchange membranes (AEMs). Herein, a novel alkaline stable polyelectrolyte is proposed by converting the electron-withdrawing C=O links in the widely used poly(aryl ether ketone) backbone into the electron-donating C-NH2 links, and then grafting faraway para-type cations by Leuckart-Menshutkin reaction without using noble metal catalysts. Contributions of the elimination of electron-withdrawing C=O links and graft of para-type cations to the excellent alkaline stability of the aryl ether containing polyelectrolytes are demonstrated through density functional theory, as the increasing electron cloud density on the ether-connected carbon atom elevates the activation energy barrier to OH- initiated aryl ether cleavage, and the para-type cation is more stable than the conventional ortho-type cation due to the sterical protection and low electrophilicity to benzylic carbon. By converting C=O to C-NH2 groups and then tuning the quaternization degree, the remaining C-NH2 groups in the polymer backbone could form hydrogen bonding networks to reinforce the membranes. The novel quaternized poly(aryl ether amine) membrane exhibits high conductivity (92.2 mS cm(-1) at 80 degrees C), excellent mechanical properties (48.2 MPa, 51.3%), and suppressed swelling ratio (12.8% at 80 degrees C). Excellent alkaline stability is also confirmed experimentally with no polymer backbone degradation even in harsh conditions (4 M KOH, 80 degrees C, 400 h), which is at the top level among the state-ofthe-art side chain and aryl ether-free types of AEMs.