Ultramicroporous Tröger's Base Framework Membranes for pH-Neutral Aqueous Organic Redox Flow Batteries

Processable polymers of intrinsic microporosity (PIMs) are emerging as promising candidates for next-generation ion exchange membranes (IEMs). However, especially with high ion exchange capacity (IEC), IEMs derived from PIMs suffer from severe swelling, thus, resulting in decreased selectivity. To solve this problem, we report ultramicroporous polymer framework membranes constructed with rigid Tröger's Base network chains, which are fabricated via an organic sol-gel process. These membranes demonstrate excellent antiswelling, with swelling ratios below 4.5% at a high IEC of 2.09 mmol g^-1, outperforming currently reported PIM membranes. The rigid ultramicropore confinement and charged modification of pore channels endow membranes with both very high size-exclusion selectivity and competitive ion conductivity. The membranes thus enable the efficient and stable operation of pH-neutral aqueous organic redox flow batteries (AORFBs). This work presents the advantages of polymer framework materials as IEMs and calls for increasing attention to extending their varieties and utilization in other applications.