Manipulating the Intrinsic Magnetism of Spinel Catalyst toward Magnetic Field-Enhanced OER

Abstract

Magnetic catalysts offer an approach to boost the sluggish kinetics of the spin-selective oxygen evolution reaction (OER) with the assistance of the spin-magnetic effect. However, the spin-magnetic effect, which is the correlation between the intrinsic magnetism and catalytic activity, has not been fully understood. Here, we manipulate the saturation magnetization (M_s) of NiCo_2–xFe_xO₄ via an iron-doping strategy and evaluate the magnetic field-assisted OER performance accordingly. The experimental results reveal a clear positive correlation between the M_s values and the magnetic field-enhanced OER activity. The ferromagnetically coupled NiCo_1.6Fe_0.4O₄ has the largest M_s of 8.6 emu g^–1, and it exhibits the strongest spin-magnetic effect, with a 14.6% reduction of the overpotential and 31.5% reduction of the Tafel slope after applying a mild magnetic field. Density functional theory (DFT) calculations demonstrate that the adsorption energy of *OH at the high-spin cobalt active site highly depends on the M_s of ferromagnetic spinel catalysts. The increase of activity is mainly attributed to the optimized e_g occupation of the high-spin cobalt ion and stronger spin-coupling between the cobalt active site and oxygenated intermediates. The elucidation of the relationship between intrinsic magnetism and field-assisted OER activity enlightens an approach toward the design of magnetic catalysts for OER and other spin-selective reactions.