Magnetic Field Enhancing the Electrocatalytic Oxygen Evolution Reaction of FeMn-Based Spinel Oxides

For the widespread application of electrolytic water hydrogen production technology, it is crucial to prepare electrolytic water catalysts via inexpensive and abundant transition metals. Commercially, Mn3O4 can be utilized extensively since it is cheap, abundant, and stable, but its electrocatalytic performance still needs to be enhanced. In this paper, we adopted the conventional hydrothermal method to introduce Fe atoms into Mn3O4 to form spinel-structured FeMn oxides on Ni foam (marked as FexMn3–xO4); then, an external magnetic field was applied to further improve its oxygen evolution reaction (OER) performance. The overpotential of FeMn2O4 is 258 mV (current density at 20 mA·cm–2), and the Tafel slope is 28.7 mV·dec–1 when the magnetic field strength is 105 mT and the angle between the electric field and the magnetic field is 45°. The introduction of Fe and the synergistic effect of the mixed Mn and Fe promote the reaction kinetics and thus improve the OER performance of Mn3O4. The enhanced performance of FexMn3–xO4 under the magnetic field may mainly originate from the magnetohydrodynamic (MHD) effect, charge transfer effect, and energy effect.