A Highly Ion‐Selective Zeolite Flake Layer on Porous Membranes for Flow Battery Applications

Zeolites are crystalline microporous aluminosilicates with periodic arrangements of cages and well‐defined channels, which make them very suitable for separating ions of different sizes, and thus also for use in battery applications. Herein, an ultra‐thin ZSM‐35 zeolite flake was introduced onto a poly(ether sulfone) based porous membrane. The pore size of the zeolite (ca. 0.5 nm) is intermediary between that of hydrated vanadium ions (>0.6 nm) and protons (<0.24 nm). The resultant membrane can thus be used to perfectly separate vanadium ions and protons, making this technology useful in vanadium flow batteries (VFB). A VFB with a zeolite‐coated membrane exhibits a columbic efficiency of >99 % and an energy efficiency of >81 % at 200 mA cm −2 , which is by far the highest value ever reported. These convincing results indicate that zeolite‐coated membranes are promising in battery applications.