Quenching-Induced Lattice Confinement Enabling Spin State Modulation in Low-Spin Mo-Doped Fe/Fe2C for Enhanced Oxygen Evolution in Anion-Exchange Membrane Water Electrolyzers

Abstract Heteroatom doping-induced lattice strain enables the reconstruction of electronic distribution, offering a promising route to efficient anion-exchange membrane water electrolysis (AEMWE). However, precisely incorporating heteroatoms into the crystal lattice to synergistically modulate the Fermi level and d-band center remains a critical challenge. Herein, a metallic salt solution quenching strategy is developed to achieve lattice-confined Mo doping into Fe/Fe2C heterostructured nanoparticles. The ultrafast cooling process creates abundant lattice defects and tensile strain, which enhance Mo 4d–Fe 3d orbital hybridization and trigger electronic transition from a high-spin to low-spin state at Fe active centers. This spin state transition reduces electron occupancy in the eg orbitals and shifts the d-band center closer to the Fermi level, thereby optimizing surface adsorption energetics for oxygenated reaction intermediates. Density functional theory calculations show that the energy barrier of the rate-determining step is reduced from 3.70 to 2.95 eV. Consequently, Mo-Fe/Fe2C exhibits improved OER catalytic performance with an overpotential of 262 mV at 10 mA cm−2, which is much lower than the pristine undoped Fe/FeC (348 mV), accompanied by a small Tafel slope of 67.8 mV dec−1. Furthermore, an AEMWE cell using this anode achieves 1.0 A cm−2 at 2.9 V, operating stably for over 250 h. Overall, this work establishes a quenching-induced lattice confinement strategy for spin state modulation, offering an effective avenue for designing advanced electrocatalysts for anion-exchange membrane water electrolyzers.