Preparation and performance of UIO-66-NH2 enhanced proton exchange membranes for vanadium redox flow batteries.

For proton exchange membranes (PEM) used in vanadium redox batteries (VRBs), doping metal-organic framework (MOF) materials to enhance the proton permeability and vanadium ion barrier property of PEM has become a research focus. In synthesizing MOFs, conventional hydrothermal method is hindered by prolonged reaction time and suboptimal material structures. This study utilizes microwave assisted heating for the preparation of UIO-66-NH2 crystals, which are then combined with Nafion to fabricate composite membranes. The results indicate that microwave heating enables a more efficient and rapid synthesis of MOF crystals (MU-NH2), with enhanced uniformity and higher yield than the conventional hydrothermal process (CU-NH2). Compared to MU-NH2/Nf-0(vanadium ion permeability: 4.4 × 10−7 cm2·min−1; ion selectivity: 5 × 104 S·min·cm−3), the vanadium ion permeability of MU-NH2/Nf-3 and CU-NH2/Nf-3 membranes exhibits a similar level of reduction, approximately 82%. Additionally, the former demonstrates an enhanced ion selectivity by 33.3%, while the latter shows an increase of 30.9%. VRBs equipped with MU-NH2/Nf membranes exhibit higher energy efficiency (83.8% at 100 mA·cm−2) and better capacity retention than those with CU-NH2/Nf membranes (82.7% at 100 mA·cm−2). Therefore, UIO-66-NH2 synthesized via the microwave method can effectively enhance the comprehensive properties of proton exchange membranes and shows promising prospects in optimizing the performance of VRBs. [ABSTRACT FROM AUTHOR]