Fabricating a Partially Fluorinated Hybrid Cation-Exchange Membrane for Long Durable Performance of Vanadium Redox Flow Batteries.

The long-term durability of vanadium redox flow batteries (VRFBs) depends on the stability and performance of the membrane separator. We have architected a hybrid membrane by uniform dispersion of MIL-101(Cr) (Cr-MOF) in a partially fluorinated polymer grafted with sulfonic acid groups (PHP@AMPS). The single cell VRFB performance of the PHP@AMPS membrane was studied in comparison with the Cr-MOF incorporated Nafion membrane (Nafion) and showed an excellent result with 97.5% Coulombic efficiency (CE) at 150 mA/cm without any significant deterioration in the charge-discharge process for 1500 cycles (over 650 h). Meanwhile, the CE value of the Nafion membrane (94.5%) deteriorated after 800 cycles (about 360 h) under similar conditions. The high VRFB performance of the PHP@AMPS membrane has been attributed to the synergized properties and good interactions between Cr-MOF and partially fluorinated polymer matrix responsible for the creation of hydrophilic proton-conducting channels to achieve high selectivity. Furthermore, the cost-effective polymer and thus membranes may open new windows for practical applications in other energy devices such as fuel cells, electrolysis, and water treatment.