Abstract
Vanadium redox flow battery (VFB) is promising for use as an energy storage/conversion device, however membrane imposes a limitation in enhancing the performance of VFB. Herein, a novel diamine monomer bis(2-trifluoromethyl-4-aminobenzene) amine containing imino groups is synthesized by nucleophilic substitution and reduction reactions. Then, we develop four branched sulfonated polyimide (I-bSPI) membranes with 40%–70% theoretical sulfonation degrees for application in VFB. The trade-off between proton conduction and vanadium ion blocking of I-bSPI membrane is broken, and the stability of I-bSPI membrane is also effectively enhanced owing to hydrogen bonds network and Donnan repulsion effect. Surprisingly, the proton selectivity of I-bSPI-50 membrane is 4.6 times that of commercial Nafion 212 membrane. In addition, I-bSPI-50 membrane exhibits superior coulomb and energy efficiencies to Nafion 212 membrane at 100–300 mA cm−2. And I-bSPI-50 membrane has steady efficiencies and high capacity holding abilities during 600-time cycles. This work illustrates a promising pathway to obtain cost-effective membrane by hydrogen bonds construction strategy for VFB application.
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