Redox-Flow Battery Based On a Nonionic Molecular Sieve Zeolite Membrane

The conventional redox-flow batteries (RFBs) use polymeric ion exchange membranes (IEMs) which have inherent shortcomings of long-term crossover of reactive ions and material instability in the highly acidic and oxidizing solutions.  Here we demonstrate the thin film of siliceous MFI-type zeolite (i.e. silicalite) as a robust electrolyte membrane for the all-vanadium RFB (VRFB). The crystalline silicalite contains uniform channels of an effective diameter of 0.56 nm that allows for the small H₃O⁺ ions to diffuse through but denies entry of the hydrated multivalent metal ions by size exclusion (steric) effect. Unlike the polymeric IEMs, the silicalite membrane is nonionic and its proton conductivity relies on the electrical field-driven H₃O⁺ transport. The VRFB equipped with the silicalite membrane has shown reduced self-discharge rate as compared to the polymer IEMs and high Coulombic efficiency in charge-discharge cycles.