Zinc–iodine redox reaction enables direct brine valorization with efficient high-water-recovery desalination

Current desalination methods, with high energy/cost demands and large volumes of brine discharged to the environment, are not sustainable. Here we propose a sustainable electrodialysis that enables direct brine valorization with efficient high-water-recovery desalination via zinc–iodine redox reactions. In a single process comprising electrodialysis and two chemical reactions in brine streams, we achieve seawater desalination with a remarkable water recovery of 90.09% without compromising other metrics (salt-removal ratio <98.29%, electric energy consumption of <2.18 kWh m⁻³). Such performance advantage is attributable to (1) high solubility of zinc–iodine-based ‘water-in-salt’ electrolytes mitigating the osmotic pressure, achieving high water recovery even for high concentration feed water (98–82% for 0.1–1.5 M) with minimal energy burdens, (2) zinc–iodine redox potential lowering electric energy demand and (3) electroconvection in the overlimiting regime enhancing desalination speed. Also, profitable ZnCl₂/NaI are electrosynthesized in brine, enabling direct valorization of desalination brines.