In Situ Engineering a Dual‐Anion Rejection Interface for High‐Efficiency Oxygen Evolution in Alkaline Seawater

Abstract Seawater electrolysis is pivotal for sustainable hydrogen production, yet chloride‐induced catalyst corrosion severely hinders its efficiency. Here, a (Mo, Co)P x electrocatalyst via a two‐step hydrothermal‐phosphorization strategy is engineered, enabling in situ formation of a dynamic dual‐anion (MoO 4 2 ⁻/PO 4 3 ⁻) Cl − ‐rejection interface. This tailored interface effectively blocks Cl − adsorption while preserving hydroxyl accessibility, significantly enhancing corrosion resistance in alkaline seawater. The optimized (Mo, Co)P x delivers exceptional oxygen evolution reaction performance in alkaline seawater electrolysis, achieving ultralow overpotentials of 213 and 360 mV to reach current densities of 10 and 1000 mA cm −2 , respectively. Remarkably, the (Mo, Co)P x with an in situ‐generated dual‐anion rejection layer demonstrates exceptional durability, exhibiting only a 20mV performance degradation during a 480‐h stability test under high‐current conditions. In situ Raman spectroscopy, in situ attenuated total reflectance surface‐enhanced infrared absorption spectroscopy, and density functional theory calculations demonstrate that the dual‐anion layer not only enhances Cl − rejection but also promotes rapid surface reconstruction of Co species and enhances interfacial water adsorption, thereby suppressing the competitive chlorine evolution reactions. This work provides a rational strategy for designing durable electrocatalysts with in situ‐engineered anion‐rejection interfaces, advancing efficient alkaline seawater electrolysis.