Ultra‐High Ion Selectivity of a Modified Nafion Composite Membrane for Vanadium Redox Flow Battery by Incorporation of Phosphotungstic Acid Coupled UiO‐66‐NH2

Abstract An ultra‐high ion‐selective Nafion composite membrane for vanadium redox flow battery (VRB) by incorporation of phosphotungstic acid (PWA) coupled UiO‐66‐NH 2 was prepared through solution casting. Simple tuning for the filling amount of the nanohybrid composed of PWA and UiO‐66‐NH 2 gives the obtained membranes preeminent vanadium barrier property including a minimum vanadium permeability of 3.46 × 10 −7 cm 2 min −1 and excellent proton transport capability including a maximum proton conductivity of 0.092 S cm −1 at 25 °C. These indicate an ion selectivity of 2.66 × 10 5 S min cm −3 , showing an overwhelming advantage over recast Nafion (0.34 × 10 5 S min cm −3 ). As a result, the VRB constructed with the modified membrane exhibits superior battery performance versus recast Nafion at various current densities.