Anion exchange membranes with high power density and energy efficiency for aqueous organic redox flow batteries

Membrane development in organic redox flow batteries (ORFBs) is of significant importance. Herein, we designed a series anion exchange membranes made from poly(p-phenylene oxide) (PPO) with different degrees functionalization, cationic moieties and crosslinking degrees. We tested them N,N,N-2,2,6,6-heptamethylpiperidinyl oxy-4-ammonium chloride/1,1′-dimethyl-4,4′-bipyridinium dichloride (TMA-TEMPO/MV) based ORFB single cell to investigate the structure-property-performance relationship. The common problem active species crossover solved by controlling membrane water uptake below 70 wt.%, resulting stable systems coulombic efficiency over 99.3%. employing prepared PPO trimethylamine moiety attached via C6-spacer achieved best overall performance. It delivered high capacity retention (94% after 100 consecutive cycles) higher peak power density (293 mW·cm−2 at 16 mL·min−1) energy (80%) than commercial reference memane FAA-3-50.