Electric Double Layer Engineering Induces O‐Down Interfacial Water Reorientation for Efficient and Long‐Term Seawater Electrolysis

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ABSTRACT Direct seawater electrolysis for hydrogen production is plagued by sluggish hydrogen evolution reaction (HER) kinetics and severe Mg/Ca hydroxide deposition, which restrict its large‐scale application. Herein, we address these two issues via a targeted electrolyte‐mediated electric double layer (EDL) engineering strategy by introducing a chelating agent, ethylene diamine tetra (methylene phosphonic acid) sodium (EDTMPS). EDTMPS adsorbed on the Pt surface effectively chelates Mg 2+ /Ca 2+ to inhibit hydroxide deposition. Meanwhile, it disrupts the hydrogen bond networks of interfacial H 2 O and increases the thickness of EDL, thereby reducing the free H 2 O reorganization energy barrier by weakening the interfacial electric field intensity. Electron transfer from Pt to EDTMPS generates a localized non‐uniform electric field, further facilitating the reorientation of H 2 O from the conventional H‐down to the more readily adsorbable O‐down configuration for HER participation inferred by second harmonic generation spectra and theoretical calculations. Simultaneously, the abundant ‐[P‐O] − groups in EDTMPS synergistically promote H 2 O dissociation with Pt active sites and accelerate the HER kinetics. The assembled natural seawater electrolyzer achieves 1.0 A cm −2 at 2.41 V and long‐term stability for over 2500 h at industrial‐level current densities. This work offers a sustainable pathway toward scalable green hydrogen production from natural seawater via electrolyte‐mediated EDL modification.

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