Hierarchical FeCoNiCuCeO_<i>x</i>/CoP Catalyst via Electrochemical Spatial Partitioning Achieves Stable Seawater Electrolysis

Seawater electrolysis offers promising hydrogen production but faces challenges from chloride corrosion, metal precipitation, and catalyst deactivation. We developed a hierarchical FeCoNiCuCeO_<i>x</i>/CoP/NF electrode using electrochemically controlled functional partitioning to overcome these limitations. Our synthesis exploits the reduction potential differences of metal ions during electrodeposition (-1.0 V vs RHE) to achieve spatial element control, creating distinct functional domains instead of random mixing. The electrode features CoP nanoneedle arrays as the conductive foundation with a multicomponent oxide layer: Cu forms conductive networks, Fe/Co/Ni provide catalytic centers, and Ce enables corrosion protection. The catalyst matches Pt/C performance in 1 M KOH (276 mV overpotential at 100 mA cm^-2, 61 mV dec^-1 of Tafel slope). In simulated seawater, performance remains excellent (296 mV overpotential) with outstanding 100-h stability. Comprehensive in situ and poststability characterization reveals that Fe, Co, and Ni components transform to oxyhydroxide active phases (Fe-OOH/Co-OOH/Ni-OOH) during operation, with multimodal evidence confirming these as the true active species responsible for enhanced performance. This demonstrates catalytic sites form through electrochemical transformation, not from as-synthesized phases. Electrochemically controlled synthesis achieves superior spatial organization compared to conventional methods, providing both practical catalyst solutions and design principles for corrosion-resistant seawater electrolysis.