Phase Transformation of Needle-Like Fe-Co_0.85Se to Hexagonal Fe-Co₃O₄ for Enhanced High-Current-Density Oxygen Evolution via Lattice Oxygen Redox

CoFe layered double hydroxide (LDH) has emerged as a promising oxygen evolution reaction (OER) electrocatalyst but exhibits low intrinsic activity and instability at high current densities, limiting industrial applicability. Herein, a phase-engineering strategy is reported to derive highly crystalline phase-transformed hexagonal Fe-Co₃O₄ (PH-FCO) via selenization of CoFe LDH to form Fe-Co_0.85Se, followed by electrochemical activation. Selective Se leaching during activation induces a morphological transition from needle-like Fe-Co_0.85Se to hexagonal PH-FCO. The resulting PH-FCO achieves a high current density of 2 A cm⁻² and maintains stability for over 300 h at 500 mA cm⁻² and 1 A cm⁻². Enhanced crystallinity formed during phase transformation effectively suppresses dissolution and preserves active catalytic sites. First-principles density functional theory calculations reveal that Fe incorporation promotes lattice oxygen oxidation, improves electronic conductivity, and reduces energy barriers. An anion exchange membrane water electrolyzer (AEMWE) incorporating PH-FCO as the anode and NiMo alloy as the cathode delivers 1.91 V at a current density of 1 A cm⁻² and maintains stable operation for over 150 h at 500 mA cm⁻². Accelerated degradation tests exhibit minimal voltage drift, confirming the robustness of PH-FCO for industrial-scale alkaline water electrolysis.