Preparation and properties of Zr-MOF-NH₂ and doped Nafion composite proton exchange membranes synthesized by microwaves

Vanadium liquid flow batteries require proton exchange membranes with excellent ion selectivity and physicochemical stability. In this work, UIO-66-NH₂ was prepared by microwave and traditional hydrothermal method, respectively, and UIO-66-NH₂/Nafion composite proton exchange membranes were prepared by the casting method, and the physicochemical properties of the membranes and the cell performance were systematically characterized. The results show that the hydrogen bonding network formed by UIO-66-NH₂ within the composite membrane, acid-base pairs and its own pore size synergistically strengthened the ion selectivity of the composite membrane. The comprehensive performance of the composite membranes base on both microwave (M/N) and traditional hydrothermal (T/N) methods is superior to that of the pure resin membrane (P-N). At the addition amount of 3 wt%, the tensile strength of the M/N-3 membrane reaches 27 MPa, the proton conductivity and vanadium ion permeability are 122.18 mS·cm⁻¹ and 0.83 × 10⁻⁷ cm²·min⁻¹, respectively, and the ion selectivity is 15.6 × 10⁵ S min cm⁻³, which is about 30 times of that of the P-N membrane, and the cell energy efficiency of this membrane reaches 83.8% - 71.7% (100-200 mA·cm⁻²), which is superior to T/N-3 membrane (82.7%-71.0%) and P-N membrane (79.4%-69.0%). The cell also shows superior cycling stability and capacity retention. Therefore, UIO-66-NH₂ synthesized by microwave method can effectively improve the comprehensive performance of proton exchange membranes, which is promising in optimizing the performance of vanadium liquid flow batteries.