Efficient and Ultrastable Seawater Electrolysis at Industrial Current Density with Strong Metal‐Support Interaction and Dual Cl ⁻ ‐Repelling Layers

Abstract Direct seawater electrolysis is emerging as a promising renewable energy technology for large‐scale hydrogen generation. The development of Os‐Ni ₄ Mo/MoO ₂ micropillar arrays with strong metal‐support interaction (MSI) as a bifunctional electrocatalyst for seawater electrolysis is reported. The micropillar structure enhances electron and mass transfer, extending catalytic reaction steps and improving seawater electrolysis efficiency. Theoretical and experimental studies demonstrate that the strong MSI between Os and Ni ₄ Mo/MoO ₂ optimizes the surface electronic structure of the catalyst, reducing the reaction barrier and thereby improving catalytic activity. Importantly, for the first time, a dual Cl ⁻ repelling layer is constructed by electrostatic force to safeguard active sites against Cl ⁻ attack during seawater oxidation. This includes a strong Os─Cl adsorption and an in situ‐formed MoO ₄ ²⁻ layer. As a result, the Os‐Ni ₄ Mo/MoO ₂ catalyst exhibits an ultralow overpotential of 113 and 336 mV to reach 500 mA cm ⁻² for HER and OER in natural seawater from the South China Sea (without purification, with 1 m KOH added). Notably, it demonstrates superior stability, degrading only 0.37 µV h ⁻¹ after 2500 h of seawater oxidation, significantly surpassing the technical target of 1.0 µV h ⁻¹ set by the United States Department of Energy.