A Dual‐Cation Exchange Membrane Electrolyzer for Continuous H2 Production from Seawater

Abstract Direct seawater splitting (DSS) offers an aspirational route toward green hydrogen (H2) production but remains challenging when operating in a practically continuous manner, mainly due to the difficulty in establishing the water supply–consumption balance under the interference from impurity ions. A DSS system is reported for continuous ampere‐level H2 production by coupling a dual‐cation exchange membrane (CEM) three‐compartment architecture with a circulatory electrolyte design. Monovalent‐selective CEMs decouple the transmembrane water migration from interferences of Mg2+, Ca2+, and Cl− ions while maintaining ionic neutrality during electrolysis; the self‐loop concentrated alkaline electrolyte ensures the constant gradient of water chemical potential, allowing a specific water supply–consumption balance relationship in a seawater–electrolyte–H2 sequence to be built among an expanded current range. Even paired with commercialized Ni foams, this electrolyzer (model size: 2 × 2 cm2) continuously produces H2 from flowing seawater with a rate of 7.5 mL min−1 at an industrially relevant current of 1.0 A over 100 h. More importantly, the energy consumption can be further reduced by coupling more efficient NiMo/NiFe foams (≈6.2 kWh Nm−3 H2 at 1.0 A), demonstrating the potential to further optimize the continuous DSS electrolyzer for practical applications.