Molybdate‐Engineered Interfacial Water Networks Enable Anti‐Precipitation Seawater Electrolysis for Stable Hydrogen Production

ABSTRACT Direct seawater electrolysis is a promising route for sustainable hydrogen production. However, its practical application is critically hindered by the rapid cathode passivation caused by the precipitation of insoluble Mg(OH) 2 , a fundamental issue that has remained unresolved. In this work, we propose a molybdate (MoO 4 2− )‐mediated interface engineering strategy by constructing a rich hydrogen‐bond water (HBW) electric double layer (EDL) to suppress cathodic precipitation. This interfacial modification effectively excludes solvated water (e.g., Mg[H 2 O] 6 2+ ) from participating in the HER, thereby preventing the local combination of Mg 2+ and OH − into insoluble precipitates. Implemented in a commercial membrane electrode assembly (MEA), this strategy enables stable operation for over 1,500 h at 100 mA/cm 2 and 1,400 h at 300 mA/cm 2 in unpretreated natural seawater. Mechanistic studies reveal that molybdate anions strengthen the hydrogen‐bonding network at the cathode interface, dynamically impeding Mg[H 2 O] 6 2+ permeation and increasing its diffusion barrier. Based on this principle, we further designed a cost‐effective NiMoP catalyst with immobilized MoO x substances. This catalyst exhibits exceptional HER activity and over 600 h stability in seawater at 300 mA/cm 2 . This work introduces a practical and highly effective anti‐precipitation strategy, unlocking the great potential of direct seawater electrolysis for sustainable hydrogen production.