Synthesis of MFe₂O₄ (M=Ni, Co) Nanoparticles by a Bicontinuous Microemulsion Method for the Oxygen Evolution Reaction

Abstract Developing efficient and low‐cost electrocatalysts for the oxygen evolution reaction (OER) is crucial for sustainable hydrogen production through water splitting. In this study, CoFe₂O₄ and NiFe₂O₄ nanoparticles as electrocatalysts were prepared via an inexpensive method involving the use of bicontinuous microemulsions as nanoreactors. The crystalline structure, morphology, and elemental composition of the electrocatalysts were characterized by XRD, Raman spectroscopy, TEM, and EDS elemental mapping. The electronic structure and textural properties were examined using XPS and the nitrogen adsorption‐desorption method. The OER measurements were carried out in a standard three‐electrode system. CoFe₂O₄ demonstrated relatively higher OER catalytic activity than NiFe₂O₄ in 1 M KOH solution, with a smaller overpotential of 410 mV to achieve a current density of 10 mA cm⁻² and a smaller Tafel slope of 80 mV dec⁻¹. In contrast, NiFe₂O₄ offered a higher overpotential of 450 mV to reach the same current density. The superior performance of CoFe₂O₄ is ascribed to higher ECSA, better conductivity, and lower charge transfer resistance. However, both electrocatalysts showed stability up to more than three hours of continuous performance.