Zincate Ion Enables M(II)-Vacancy NiFe Layered Double Hydroxide for Stable Seawater Electrolysis at 3 A cm^-2

Seawater electrolysis offers a sustainable route for hydrogen production. Operating at high current densities can improve the energy efficiency but requires anodes that can sustain high oxygen evolution reaction (OER) activity, selectivity, and stability against negative effects of Cl^-. Herein, NiFeZn layered double hydroxide (NiFeZn-LDH) demonstrates remarkable OER performance, requiring only 220 mV overpotential to achieve 10 mA cm^-2, and maintaining 100% selective seawater oxidation to oxygen for 500 h at an unprecedented current density of 3 A cm^-2, with minimal degradation. Through comprehensive characterizations, it is found that the dissolution of the amphoteric Zn-site and the following formation of Zn²⁺ vacancies are key to the excellent OER activity. The free Zn²⁺ in electrolyte converts to Zn(OH)₄ ^2- and adsorbs onto the electrode, facilitating the OH^- nucleophilic attack by disrupting the hydrogen bond network at the electrochemical interface. Furthermore, the steric hindrance of Zn(OH)₄ ^2- suppresses the Cl^- competing adsorption, ensuring 100% OER selectivity and long-term stability. As a result, an industrial-scale electrolyzer with NiFeZn-LDH as the anode operates stably for over 700 h in a saturated NaCl electrolyte, consuming only 4.26 Nm^-3 H₂. This work demonstrates the feasibility of developing energy-efficient, highly stable seawater electrolyzers that outperform conventional water electrolyzers.