Magnetic-field guided synthesis of highly active Ni–S–CoFe2O4 electrocatalysts for oxygen evolution reaction

The sluggish kinetics of the four-electron-proton coupled oxygen evolution reaction (OER) limits the efficiency of water splitting. Herein, Ni–S–CoFe2O4 magnetic nanosheets supported on Ni Foam (Magn-Ni-S-CoFe2O4/NF) as highly active OER electrocatalysts are synthesized via an extremely simple magnetic-field guided co-electrodeposition strategy. With the application of magnetic fields, the flower-like structures consisting of numerous nanosheets are obtained. This special interconnected structure can effectively reduce the transfer resistance to electrons during catalysis. The ultra-thin amorphous Ni–S layer at the edge of well-defined crystalline CoFe2O4 provides more active sites for the reaction because of the abundant defects, which greatly enhances the OER performance. At the same time, the application of magnetic fields changes the chemical state of the electrocatalyst. The well-designed Magn-Ni-S-CoFe2O4/NF exhibits excellent OER activity with a low overpotential of 228 mV at the current density of 10 mA cm−2, which is lower than the value of 253 mV for the Ni–S–CoFe2O4/NF without applied magnetic field, a small Tafel slope of 72 mV dec−1 and excellent stability for at least 24 h. This work provides a simple magnetic field-assisted synthesis method to prepare electrocatalysts with excellent OER activity.