Photothermal–Magnetic Synergistic Effects in an Electrocatalyst for Efficient Water Splitting under Optical–Magnetic Fields

Abstract The slow oxygen evolution reaction (OER) limits water splitting, and external fields can help improve it. However, the effect of a single external field on the OER is limited and unsatisfactory. Furthermore, the mechanism by which external fields improve the OER is unclear, particularly in the presence of multiple fields. Herein, a strategy is proposed for enhancing the OER activity of a catalyst using the combined effect of an optical–magnetic field, and the mechanism of catalytic activity enhancement is studied. Under the optical–magnetic field, Co₃O₄ reduces the resistance by increasing the catalyst temperature. Meanwhile, CoFe₂O₄ further reduces the resistance via the negative magnetoresistance effect, thus decreasing the resistance from 16 to 7.0 Ω. Additionally, CoFe₂O₄ acts as a spin polarizer, and electron polarization results in a parallel arrangement of oxygen atoms, which increases the kinetics of the OER under the magnetic field. Benefiting from the optical and magnetic response design, Co₃O₄/CoFe₂O₄@Ni foam requires an overpotential of 172.4 mV to reach a current density of 10 mA cm⁻² under an optical–magnetic field, which is significantly higher than those of recently reported state‐of‐the‐art transition‐metal‐based catalysts.