Modulation of the Phase Transformation of Fe₂O₃ for Enhanced Water Oxidation under a Magnetic Field

Abstract

Ferromagnetic catalysts in the presence of an external magnetic field can promote the reaction kinetics of the oxygen evolution reaction (OER) by enhancing spin-selective electron transfer as intermediates and products confer spin-dependent behavior. It has been found that γ-Fe2O3 with ferromagnetism exhibits an enhanced performance for the OER activity, but its preparation is limited. Herein, we report an adsorption-pyrolysis process in air in which the transformation of α-Fe2O3 into γ-Fe2O3 is precisely regulated by controlling the content of Co ions. Interestingly, a small, constant external magnetic field (∼200 mT) was applied at the anode, resulting in a significant impact on the OER performance of the obtained series of catalysts with different contents of γ-Fe2O3 under alkaline conditions. Theoretical results reveal that the same spin configuration of Fe and O atoms in γ-Fe2O3 provides a spin conduction channel, which enhances the ability to selectively remove spin-oriented electrons from the reactants and accelerates the accumulation of triplet oxygen molecules during the OER process, thereby promoting the OER. These findings provide a strategy toward the controllable phase transformation of Fe2O3 and deep insights for understanding the OER behavior of Fe-based electrocatalysts under magnetic fields.