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 spindependent behavior. It has been found that γ-Fe 2 O 3 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-Fe 2 O 3 into γ-Fe 2 O 3 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-Fe 2 O 3 under alkaline conditions. Theoretical results reveal that the same spin configuration of Fe and O atoms in γ-Fe 2 O 3 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 Fe 2 O 3 and deep insights for understanding the OER behavior of Fe-based electrocatalysts under magnetic fields.

The mechanism of water oxidation using transition metal-based heterogeneous electrocatalysts

“…Transition metal-based catalysts (Fe, Co, and Ni) exhibit catalytic activity comparable to that of iridium and ruthenium-based OER catalysts. 38,152–154 The OER activity of iron-based catalysts is not as good as that of nickel-based or cobalt-based catalysts because of their poor conductivity. In general, OER performance is highly correlated with the adsorption strength of oxygen-containing intermediates to the active site.…”