Modification of Nafion membrane using fluorocarbon surfactant for all vanadium redox flow battery

Fluorocarbon surfactant (potassium nonafluoro-1-butanesulfonate) is employed to prepare the Nafion/fluorocarbon (N/FC) membranes for all vanadium redox flow batteries (VRFB). N/FC membranes with different FC surfactant mass ratios were successfully prepared by a solution casting method. The addition of FC surfactant has effectively suppressed the vanadium ions permeability and improved the proton conductivity of Nafion . The N/FC membrane with 5   wt% of FC surfactant (N/FC—5%) exhibits the highest ion selectivity (ratio of proton conductivity to permeability) of 2.0×10 6   S   min   cm −3 , which is 2.1 times higher than that of pure recast Nafion (r-Nafion) membrane (9.7×10 5   S   min   cm −3 ). Consequently, both coulombic efficiency ( CE ) and voltage efficiency ( VE ) of the VRFB with N/FC—5% membrane are higher than that of the VRFB with r-Nafion membrane. The average energy efficiency (product of CE and VE ) of the VRFB with N/FC—5% membrane is 11% higher than that of the VRFB with r-Nafion at current density of 40–80   mA   cm −2 .