Phase Formation and Elemental Transport in the Electrosynthesis of Nickel Ferrite by Sacrificial Iron Anode in Nickel Salt Solution

Electrochemical methods are promising for the synthesis of ferrite particles with controlled sizes and morphologies. Nevertheless, the mechanisms of particle formation in these systems are still unclear. Here, we report the mechanisms of nickel ferrite (NiFe₂O₄) particle formation via an electrochemical method. Specifically, the iron anode was electrooxidized in a nickel salt solution, and the generated particles were sampled and characterized for their composition and crystal phase. High-purity NiFe₂O₄ particles were obtained at high voltages, whereas impurities in the form of β-Ni(OH)₂ and β-FeOOH existed at low voltages. Magnetite (Fe₃O₄) nuclei were initially formed when an appropriate proportion of Fe(OH)₂ and FeOOH in solution was attained. The growth of NiFe₂O₄ was caused by the diffusion of Ni atoms from the solution to the surface of the generated Fe₃O₄ particles, followed by atomic substitution. Ni diffusion toward the Fe₃O₄ powder surface and then through the Fe₃O₄ lattice started only after the formation of Fe₃O₄. The formation rate of Fe₃O₄ increased with increasing voltage. These results provide invaluable insight into the mechanisms of the formation of ferrite particles using a promising synthesis route for the production of ferrite particles in an electrochemical system.