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 of anion exchange membranes made from poly(p-phenylene oxide) (PPO) with different degrees of functionalization, cationic moieties and crosslinking degrees. We tested them in a 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 of active species crossover is solved by controlling the membrane water uptake below 70 wt.%, resulting in stable systems with coulombic efficiency of over 99.3%. The cell employing a membrane prepared from PPO and trimethylamine moiety attached via a C6-spacer achieved the best overall cell performance. It delivered high capacity retention (94% after over 100 consecutive cycles) and higher peak power density (293 mW center dot cm(-2) at 16 mL center dot min(-1)) and energy efficiency (80%) than the commercial reference memane FAA-3-50.

Automated summary

Membrane development is crucial in organic redox flow batteries (ORFBs). In this study, a series of anion exchange membranes made from poly(p-phenylene oxide) (PPO) with different functionalization degrees, cationic moieties, and crosslinking degrees were designed. The membrane prepared from PPO and trimethylamine moiety attached via a C6-spacer showed the best overall cell performance, with high capacity retention (94% after over 100 consecutive cycles), higher peak power density (293 mW center dot cm(-2) at 16 mL center dot min(-1)), and energy efficiency (80%) compared to the commercial reference membrane FAA-3-50.