Efficient Membranes Made of a Nanohybrid of Fluorine‐Doped Carbon Dots Coupled With Metal Organic Framework for High‐Performance Vanadium Redox Flow Battery

ABSTRACT The commercially available membranes for vanadium redox flow battery (VRFB) suffer from severe vanadium ion crossover, resulting in less than satisfactory stability with the batteries. Herein, a sulfonated poly(ether ether ketone)‐based membrane incorporating fluorine‐doped carbon dots (FCD) and functionalized metal–organic framework (MIL−101−NH 2 ) nanohybrids (FCDM) is developed for VRFB. The incorporation of FCDM into the hybrid membrane is found to promote proton conduction thanks to the porous structure and functional amine groups of MIL−101−NH 2, which provide abundant pathways for proton conduction, while FCD further enhances the interface compatibility with the polymer matrix and provides additional active sites for proton transport. In addition, the FCD modulates the pores of MIL−101−NH 2 , further regulating the ion transport channels and effectively inhibiting vanadium ion permeability to achieve high ion selectivity. Consequently, the VRFB with the optimized hybrid membrane delivered high Coulombic efficiency (99.75%) and energy efficiency (85.6%) at 120 mA cm −2 over 1000 cycles. Furthermore, the capacity retention of the batteries with the hybrid membrane (81.5%) is 10‐fold higher than that of the commercial Nafion 212 membrane (8.1%) under the same conditions. The superior performance of the hybrid membranes suggests a promising strategy for designing next‐generation membranes with tailored nanostructures for VRFB.