Interfacial OH- Dynamic Modulation by Alternating Current Enables Precipitation-Suppressed Direct Seawater Electrolysis for Hydrogen Production.

Direct seawater electrolysis (DSE) for H2 production suffers from severe performance degradation caused by the precipitation of Mg/Ca hydroxides, where OH- generated from the hydrogen evolution reaction (HER) reacts with Mg2+/Ca2+ in seawater. To address this issue, we propose an innovative alternating current-driven DSE (AC-DSE) instead of conventional direct current-driven DSE (DC-DSE). Periodic polarity reversal under AC enables the same electrode to alternately function as cathode and anode, ensuring OH- from HER is promptly consumed by subsequent anodic OH--consuming reaction. This dynamic interfacial OH- modulation prevents local alkalization and precipitation. Proof-of-concept experiments using PtRh electrodes validated that AC-DSE effectively prevents precipitation and maintains a stable current, in contrast to the rapid precipitation and performance decay observed in DC-DSE. FEM simulations and experimental established the optimal AC waveform and period for effective precipitation-suppressed and high Faradaic efficiency. Furthermore, by replacing the oxygen evolution reaction with ethylene glycol oxidation (EGOR), a reaction typically requiring strong alkali, the AC‑driven local microenvironment enables efficient HER‑EGOR coupling in neutral seawater. Importantly, this HER‑EGOR coupling system eliminates H2/O2 mixing risks, lowers energy consumption and co-produces value‑added chemicals. This work establishes AC-DSE as an effective and promising route for sustainable H2 production from seawater.