Dual‐Phase Activation and Mo‐Mediated Interfacial Stabilization Enable Active and Durable Seawater Oxidation on a Monolithic High‐Entropy Alloy Electrode

Seawater oxygen evolution reaction (OER) anodes require high activity and long‐term durability in chloride‐containing electrolytes, yet reconstructed active interfaces are often destabilized by halide‐induced corrosion and dissolution. To address this issue, we report a Mo‐containing dual‐phase nanoporous high‐entropy alloy electrode that integrates phase‐selective activation with Mo‐mediated interfacial stabilization. By comparing Mo‐free single‐phase, Mo‐free dual‐phase, and Mo‐containing dual‐phase electrodes, we distinguish the respective contributions of the dual‐phase architecture and Mo incorporation to OER activity and stability. The FCC/B2 dual‐phase architecture enlarges the electrochemically accessible interface through selective activation of the FCC‐derived region. Mo incorporation further improves the apparent site‐normalized OER activity and assists the formation of a continuous Ni‐rich mixed oxyhydroxide/oxide reconstructed layer. Time‐dependent analysis reveals a cooperative reconstruction process, where the B2‐type phase preserves the structural framework and further consumption of the FCC‐derived region becomes strongly limited after surface‐layer formation. Consequently, the Mo‐containing dual‐phase electrode operates for over 10 000 h at 1000 mA·cm −2 in 6.0 M KOH + 1.5 M NaCl and over 3500 h at 200 mA·cm −2 in 1.0 M KOH + natural seawater. This work provides a structure‐interface cooperative strategy for active and durable alkaline seawater OER anodes.