Sulfonated poly(ether-ether-ketone) membranes with intrinsic microporosity enable efficient redox flow batteries for energy storage

T Wong and YJ Yang and R Tan and AQ Wang and Z Zhou and ZZ Yuan and JX Li and DZ Liu and A Alvarez-Fernandez and CC Ye and M Sankey and D Ainsworth and S Guldin and F Foglia and NB McKeown and KE Jelfs and XF Li and QL Song, JOULE, 9, 101795 (2025).

DOI: 10.1016/j.joule.2024.11.012

Redox flow batteries (RFBs) are promising for long-duration grid-scale sustainable energy storage. The ion-exchange membrane is a key component that determines energy efficiency and cycling stability. However, it remains challenging to develop membranes with high ionic conductivity and high selectivity toward redox-active electrolytes. We report the development of ion-conductive polymer membranes with record-breaking energy efficiency. By incorporating triptycene into poly(ether-ether- ketone) and controlled sulfonation, the resulting intrinsically microporous polymer membranes form highly interconnected water channels that facilitate transport of charge-balancing ions, particularly hydroxide anions. These microporous membranes showed high ionic conductivity without compromising the selectivity toward redox-active species. The membranes enabled excellent performance in alkaline aqueous organic and zinc-iron flow batteries, demonstrating long-term stability, high power density, and an operational current density up to 700 mA cm(-2). The membranes also improved performance in neutral pH aqueous RFBs with high capacity utilization and retention, enhanced energy efficiency, and boosted power density.

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