In Situ Growth of Amorphous NiFe Hydroxides on Spinel NiFe₂O₄ via Ultrasonic-Assisted Reduction for an Enhanced Oxygen Evolution Reaction

Amorphous Ni–Fe hydroxides (NiFe­(OH)_x) are considered to possess promising potential as oxygen evolution reaction (OER) electrocatalysts, but amorphous NiFe­(OH)_x is hard to synthesize due to the complicated multistep synthesis process. Herein, amorphous NiFe­(OH)_x is successfully grown in situ on the surface of NiFe₂O₄ via an ultrasonic-assisted reduction method. This method takes advantage of ultrasonic cavitation to achieve a unique reduction effect, migration of Ni and Fe cations of NiFe₂O₄ to the crystal surface, and in situ growth of amorphous NiFe­(OH)_x, thereby forming a NiFe₂O₄/NiFe­(OH)_x composite. This material exhibits enhanced electrochemical performance with an overpotential of 276 mV at 10 mA cm^–2. The ultrasonic-assisted reduction method can be used to synthesize amorphous NiFe­(OH)_x with no residual reactants, providing a simple and facile way to synthesize amorphous hydroxide materials.