Reconstruction of Ferromagnetic/Paramagnetic Cobalt‐Based Electrocatalysts under Gradient Magnetic Fields for Enhanced Oxygen Evolution

Abstract The rational manipulation of the surface reconstruction of catalysts is a key factor in achieving highly efficient water oxidation, but it is a challenge due to the complex reaction conditions. Herein, we introduce a novel in situ reconstruction strategy under a gradient magnetic field to form highly catalytically active species on the surface of ferromagnetic/paramagnetic CoFe 2 O 4 @CoBDC core–shell structure for electrochemical oxygen evolution reaction (OER). We demonstrate that the Kelvin force from the cores’ local gradient magnetic field modulates the shells’ surface reconstruction, leading to a higher proportion of Co 2+ as active sites. These Co sites with optimized electronic configuration exhibit more favorable adsorption energy for oxygen‐containing intermediates and lower the activation energy of the overall catalytic reaction. As a result, a significant enhancement in OER performance is achieved with a large current density increment about 128 % at 1.63 V and an overpotential reduction by 28 mV at 10 mA cm −2 after reconstruction. Interestingly, after removing the external magnetic field, the activity could persist for over 100 h. This work showcases the directional surface reconstruction of catalysts under a gradient magnetic field for enhanced water oxidation.