Synergy effects of hindered phenol and diphosphite antioxidants on promoting alkali resistance of quaternary ammonium functionalized poly(4-vinylbenzyl chloride-styrene) anion exchange membranes

On the Radical-Induced Degradation of Quaternary Ammonium Cations for Anion-Exchange Membrane Fuel Cells and Electrolyzers

Four benzylic-type quaternary ammonium (QA) compounds with different electron density at the phenyl group were evaluated for their susceptibility against degradation by radicals. Time-resolved absorption spectroscopy indicated that radicals with oxidizing and reducing character were formed upon oxidation by HO⋅ and O⋅^- (conjugate base of HO⋅). It was estimated that, dependent on the QA, 18-41 % of the formed radicals were oxidizing with standard electrode potentials (E⁰ ) above 0.276 V and 13-23 % exceeded 0.68 V, while 13-48 % were reducing with E⁰ <-0.448 V. The stability of these model compounds against oxidation and reductive dealkylation was evaluated at both neutral and strongly alkaline conditions, pH 14. Under both conditions, electron-donating groups promoted radical degradation, while electron-withdrawing ones increased stability. Therefore, durability against radical-induced degradation shows an opposite trend to alkaline stability and needs to be considered during the rational design of novel anion-exchange membranes for fuel cells and electrolyzers.

New block poly(ether sulfone) based anion exchange membranes with rigid side-chains and high-density quaternary ammonium groups for fuel cell application

We report a series of novel poly(ether sulfone) based anion exchange membranes (AEMs) with relatively good stability due to their rigid side-chains and heterocyclic quaternary ammonium groups. The AEMs show appropriate performance in AEM fuel cells.