Reconstruction-Induced Bilayered Amorphous-Crystalline Hybrid NiOOH-Based Anode for Ultrastable Seawater Electrolysis

Direct seawater electrolysis represents a critical pathway for large-scale utilization of renewable energy in coastal and island regions without potential impacts on freshwater supply, yet being severely hindered by the corrosion of electrode materials in seawater. Conventional anion-based protection strategies often suffer from lattice degradation during activation or anion desorption in operation. Herein, we report a facile electrodeposition-anodization synthesized amorphous-crystalline hybrid NiFeCoCr anode featuring a vertically bilayered architecture, enabling ultrastable seawater oxidation for over 15 000 h at 500 mA cm^-2. During anodization, the partial sacrificial leaching of Cr forms an amorphous β-NiOOH phase surface layer, exposing abundant active sites to enhance OER activity. Concurrently, in situ generated CrO₄ ^2- anions stably adsorb and intercalate within the dense crystalline Fe/Co-doped γ-NiOOH underneath layer. The electrolyzer assembled with the NiFeCoCr anode delivers stable operation for over 2500 h in alkaline natural seawater and for 240 h in alkaline saturated NaCl electrolyte at 80°C.