A Bunch-Like Tertiary Amine Grafted Polysulfone Membrane for VRFBs with Simultaneously High Proton Conductivity and Low Vanadium Ion Permeability

Novel polysulfone membranes with bunch-like tertiary amine groups are synthesized with high ion selectivity and outstanding chemical stability for vanadium redox flow batteries (VRFBs). The bunch-like tertiary amine groups simultaneously act as an ionic conductor for proton hopping and vanadium ion transport obstacles. The performance of the membrane is tuned via controlling the grafting degree of the chloromethylated polysulfone. The results show that membranes show increasing proton over vanadium ion (σ/p) selectivity with increasing functional tertiary groups. VRFBs assembled with the prepared membranes demonstrate an impressive Coulombic efficiency of 98.9% and energy efficiency of 90.9% at a current density of 50 mA cm−2. Furthermore, the prepared membrane reported in this work shows excellent stability in 1 m VO2 + solution at 35 °C over 240 h. Overall, the synthesized polymers provide a new insight into the design of high-performance membranes toward VRFB applications.