Anion‐Regulated Corrosion‐Driven Scalable Synthesis of Nickel‐Iron Electrodes for Efficient Oxygen Evolution

ABSTRACT Corrosion‐derived nickel‐iron layered double hydroxides (NiFe‐LDH) on iron (NiFe@Fe) are promising oxygen evolution reaction (OER) electrodes for cost‐effective green hydrogen production. However, the influence of anions in corrosion solutions on their structure and catalytic behavior remains elusive. Here, NiFe@Fe‐X (X = SO 4 , Cl, NO 3 ) electrodes are prepared using NiSO 4 , NiCl 2 , Ni(NO 3 ) 2 solutions. Structural analyses demonstrate that NiFe@Fe‐SO 4 comprises an iron core, a nickel interlayer, and a Fe 2+ ‐doped NiFe‐LDH shell, whereas NiFe@Fe‐Cl forms an additional α‐FeOOH overlayer due to Cl − ‐accelerated iron corrosion. In contrast, oxidative NO 3 − produces an iron‐oxide interlayer and a Fe 2+ ‐free NiFe‐LDH shell with α‐FeOOH coating. Despite structural distinctions, all NiFe@Fe‐X share the same active phase (nickel‐iron oxyhydroxides) and reaction pathway. Among them, NiFe@Fe‐SO 4 delivers the highest OER activity, attributed to Fe 2+ doping of NiFe‐LDH, a conductive interlayer, and a porous NiFe‐LDH shell without α‐FeOOH blockage that minimizes kinetic, ohmic, and mass‐transport losses. NiFe@Fe‐SO4 delivers 500 mA cm −2 at 1.56 V with remarkable stability (−4 µV h −1 ) over 800 h in an alkaline water electrolyzer (1 cm 2 active area) and can be further upscaled to 2 m × 0.3 m, underscoring its industrial viability. This work offers fundamental insights into anion‐regulated corrosion chemistry and design principles for efficient OER electrodes.