Direct Electrosynthesis and Separation Platform for Chlorine from Saline Water

Electrosynthesis of chlorine (Cl₂) from seawater and natural and industrial brines emerges as a transformative approach for wastewater valorization while achieving water purification. However, the effective separation of chlorine from complex saline mixtures and the mitigation of environmental impacts from chlorine derivatives are two critical challenges to tackle. Here, we report a scalable electrosynthesis platform capable of producing and separating chlorine directly at a single three-phase interface, achieving up to 97% selectivity and nearly 100% separation efficiency. Employing a three-stacked modular electrolyzer, we successfully generated sodium hypochlorite solutions at concentrations of 0.53 and 5.1 wt % from real reverse osmosis retentate and seawater. The treated brine discharge met the stringent environmental standards for chlorine-based contaminants. Compared to ion exchange and electrodialysis, this upcycling and separation process has the potential to advance decentralized chlor-alkali production and nonpotable water generation. Additionally, it can be seamlessly integrated with direct or indirect electrochemical impure water splitting, eliminating low-value oxygen production, reducing the need for alkali additives, and addressing safety concerns such as hydrogen/oxygen crossover.