Initiating a composite membrane with a localized high iodine concentration layer based on adduct chemistry to enable highly reversible zinc-iodine flow batteries.

The issue of polyiodide crossover at an iodine cathode significantly diminishes the efficiency and practicality of aqueous zinc-iodine flow batteries (ZIFBs). To address this challenge, we have introduced a localized high iodine concentration (LHIC) coating layer onto a porous polyolefin membrane, which featured strong chemical adsorption by exploiting adduct chemistry between the iodine species and a series of low-cost oxides, , MgO, CeO, ZrO, TiO, and AlO. Leveraging the LHIC based on the potent iodine adsorption capability, the as-fabricated MgO-LHIC composite membrane effectively mitigates iodine crossover Donnan repulsion and concentration gradient effects.