Anion Exchange Membranes by Bromination of Benzylmethyl-Containing Poly(sulfone)s

Abstract

This report details the properties of anion-conducting membranes synthesized by halomethylation and quaternization of benzylmethyl-containing poly(sulfone)s. The benzylmethyl moieties, which serve as precursors to cationic sites, are introduced during polymer synthesis, thereby circumventing postmodification of the polymer by chloromethylation. By directing the distribution of ionic groups, the anion conductivity and water uptake of the membranes could be tuned over a wide range. For homogeneously distributed cationic groups, the water uptake and anionic conductivity were high relative to the material's ion exchange capacity. When an unfunctionalizable comonomer was added, the water uptake decreased for a given ion content. A strong correlation between the water uptake and anion conductivity was observed for all materials. Interestingly, as the cation concentration in the membrane decreased due to an increase in water uptake, the anion conductivity increased. This unexpected relationship between the volumetric density of fixed charged sites and the anion conductivity underscores the importance of water uptake in these materials to promote fast anion transport.

A Highly Hydroxide Conductive, Chemically Stable Anion Exchange Membrane, Poly(2,6 dimethyl 1,4 phenylene oxide)-b-Poly(vinyl benzyl trimethyl ammonium), for Electrochemical Applications

“…An ideal AEM should have high ionic conductivity to achieve practical power densities, 3 good chemical stability to operate under an alkaline environment, 4 and excellent thermal and mechanical properties to survive transient operating conditions. 1,5 Intensive efforts have been made to study AEMs with aromatic backbones such as polysulfone, [6][7][8] poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), [9][10][11] and poly(ether ether ketone) 12 due to their high thermal and chemical stability, good mechanical properties, and outstanding film forming ability. 13 PPO is a versatile aromatic polymer, which can advantageously be used as a precursor in the preparation of graft, 14 random and copolymers as studied by previous researchers for AEM applications.…”

Densely quaternized anion exchange membranes synthesized from Ullmann coupling extension of ionic segments for vanadium redox flow batteries

“…Water uptake, swelling ratio and anion conductivity Anion conductivity is a core property of AEMs, which is mainly affected by IEC, ion distribution, and water uptake [40]. In order to investigate the relationship among them, the water uptake, swelling ratio and anion conductivity of QA-OMPFEKs with different IECs and counter-ions were measured.…”

Strategies for Developing New Anion Exchange Membranes and Electrode Ionomers

“…Figure 3 compares free-radical bromination and chloromethylation routes for similar poly(sulfone)-type AEMs. [50][51][52] The extra step required in the bromination route to synthesize benzylmethyl-containing polymers can impose a large barrier to scale-up since introducing a new polymer to the market is difficult. Therefore, leveraging commercial polymer backbones and appropriate modification chemistries that can be practiced at scale is important going forward.…”