Tuning the Electronic Structure of Ni₂P through Fe Doping to Trigger the Lattice-Oxygen-Mediated Oxygen Evolution Reaction

Developing cost-effective electrocatalysts for efficient seawater splitting requires a fundamental understanding of the oxygen evolution reaction (OER) mechanism. Herein, iron-doped nickel phosphide (Fe-Ni₂P) is synthesized via a hydrothermal-impregnation-phosphidation strategy to investigate the role of Fe incorporation in modulating the electronic structure and OER pathways. Mechanistic investigations demonstrate that Fe doping triggers a shift from adsorbate evolution mechanism (AEM) to lattice oxygen-mediated (LOM) pathways, evidenced by pH-dependent kinetics, tetramethylammonium cation probing, and in situ electrochemical impedance spectroscopy (EIS). The LOM mechanism involves nonconcerted proton-electron transfers, facilitated by accelerated hydroxide adsorption (<i>k</i>_s = 0.275 s^-1) and dynamic surface reconstruction into amorphous NiOOH. The reduced activation energy (27.1 kJ mol^-1) and lower charge-transfer resistance in Fe-Ni₂P underscore its superior thermodynamics and kinetics. X-ray photoelectron spectroscopy and EIS further validate lattice oxygen activation and oxygen vacancy accumulation during the OER process. Electrochemical studies reveal that Fe-Ni₂P exhibits a low overpotential of 220 mV at 10 mA cm^-2 and remarkable stability through phosphate-mediated Cl^- repulsion and dynamic surface reconstruction involving lattice oxygen activation in alkaline seawater. This work establishes Fe-induced electronic modulation as a critical strategy for activating LOM-dominated catalysis in transition metal phosphides.