Nonionic zeolite membrane as potential ion separator in redox-flow battery

• Demonstrated high proton permselectivity in the nonionic silicalite membrane.
• The membrane's proton/metal ion selectivity relies on size-exclusion (steric) effect.
• Demonstrated the silicalite membrane as an ion separator for vanadium redox-flow battery.
• Zeolite membranes can be an alternative class of IEM for redox-flow batteries.

The crystalline silicalite membrane has been demonstrated as an effective ion separator for acidic solutions of vanadyl sulfate and for potential application as a proton-permselective electrolyte membrane in the all-vanadium redox-flow battery. Silicalite contains uniform channels with an effective diameter of 0.56 nm, which permits the small H3O+ ions to diffuse through but is impermeable to the large hydrated multivalent vanadium ions due to steric effects. Unlike conventional polymeric ion exchange materials, silicalite is nonionic and its proton conductivity relies on the electric field-driven H3O+ transport through the sub-nanometer pores. The silicalite membrane exhibits high proton selectivity relative to vanadium ions and a significantly reduced self-discharge rate compared to that of Nafion ion exchange membranes.