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

Direct seawater splitting (DSS) offers an aspirational route toward green hydrogen (H-2) 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 H-2 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-H-2 sequence to be built among an expanded current range. Even paired with commercialized Ni foams, this electrolyzer (model size: 2 x 2 cm(2)) continuously produces H-2 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 (approximate to 6.2 kWh Nm(-3) H-2 at 1.0 A), demonstrating the potential to further optimize the continuous DSS electrolyzer for practical applications.