Decoupled Dual‐Stream Seawater Electrolysis Toward Cost‐Effective Green Hydrogen Production

Ocean, as a vast natural reservoir of ionic minerals, provides a promising approach to offset the high cost of hydrogen production from electrocatalytic water splitting. However, the complex ionic environment of seawater compels us to separate out scaling‐prone ions via cost‐effective membrane separation technology, and further separately electrolyze diluted and concentrated seawater to produce H 2 and high value‐added marine chemical products. We herein apply electrodialysis to separate out divalent cations and produce twofold concentrated seawater and fresh seawater. A decoupled dual‐stream seawater electrolysis (DDSE) strategy is designed. The fresh seawater is routed into an alkaline/AEM water electrolyzer to sustain stable H 2 evolution. The concentrated seawater is fed into a home‐made electrolyzer to produce NaClO and high‐purity Mg(OH) 2 . A scalable non‐noble metal‐based electrode (50 cm × 50 cm) was designed and fabricated with high activity and stability when applied in the chlorine evolution reaction. System‐level evaluation validates the feasibility of the DDSE strategy. Through rigorous techno‐economic analysis, the unit price of H 2 production is reduced to $0.39 kgH 2 −1 (DOE 2030 target: $1 kgH 2 −1 ), and the Global Warming Potential can be reduced up to 6.83%. This proposed DDSE strategy offers a new approach for cost‐effective green hydrogen production with comprehensive seawater valorization.