Phase Transformation of Needle‐Like Fe‐Co0.85Se to Hexagonal Fe‐Co3O4 for Enhanced High‐Current‐Density Oxygen Evolution via Lattice Oxygen Redox

Abstract 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‐Co 3 O 4 (PH‐FCO) via selenization of CoFe LDH to form Fe‐Co 0.85 Se, followed by electrochemical activation. Selective Se leaching during activation induces a morphological transition from needle‐like Fe‐Co 0.85 Se 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.