Strain Engineering of Hematite Nanoparticles via Electronically Inert Mg2+ Doping toward Enhanced Oxygen Evolution Reaction

Strain engineering has emerged as an effective strategy to regulate the electronic structure of nonprecious transition-metal-based electrocatalysts for enhanced oxygen evolution reaction (OER) activity. Nevertheless, in most reported electrocatalyst systems, the use of other catalytically active transition metal ion dopants couples strain effects with dopant-derived d electronic configuration modifications and even active sites, thereby obscuring the intrinsic role of lattice strain. Herein, strain-dominant engineering of hematite (α-Fe2O3) for efficient OER was achieved via electronically inert Mg2+ doping. Combined experimental and theoretical analyses revealed that Mg2+ substitution induces lattice expansion and intrinsic tensile strain in the α-Fe2O3 lattice, which modulates the local Fe–O coordination environment and enhances Fe–O orbital interaction, thereby leading to more favorable adsorption energetics of OER intermediates. As a result, Mg2+-doped α-Fe2O3 nanoparticles with optimized Mg2+ content of 1.53% exhibited a substantially reduced overpotential, delivering a current density of 10 mA cm–2 at 0.406 V compared to 0.453 V for pristine α-Fe2O3, along with a significantly decreased Tafel slope from 161.5 to 99.6 mV dec–1. This work establishes electronically inert dopant-induced strain engineering as an effective strategy for enhancing the electrocatalytic performance of iron-based oxide nanocatalysts by regulating Fe–O orbital coupling and oxygen intermediate adsorption.