Evaluation of Mg2+-substituted NiFe2O4 as a green anode material

In recent years, the awareness of energy, environment and economy for the metallurgical industries, has necessitated the development of mixed oxide-based oxygen-evolving anode materials to avoid the emission of greenhouse gases, such as CO2, CO, and CF6, during electrolysis. In this regard, the noncarbon anode material Ni1-xMgxFe2O4 (x = 0.0, 0.3, 0.6, 0.9) has been prepared by nonconventional citrate gel process using metal nitrate salts as cation precursors and citric acid as a chelating agent. The X-ray analysis showed the existence of single-phase spinel structure with increase of lattice parameter and tetrahedral radius with increasing Mg2+ ion concentration, as against a decrease in density. The FT-IR spectra show the characteristic features of the synthesized ferrite compounds. The DC electrical conductivity increases with increasing temperature. It also increases with an increase of Mg2+ ion concentration and reaches a maximum value of 3.3 S cm-1 at x = 0.6 at which, the activation energy for conduction is found to be minimum. The effect of the Mg2+ substitution on the electrocatalytic activity of the electrodes towards the oxygen evolution reaction (OER) is studied by using steady state potentiostatic polarization measurements in alkaline KOH solution. The Roughness factor (Rf) and the Double layer capacitance (Cdl) of the synthesized electrodes were measured by using Electrochemical Impedance Spectroscopy. The chemical stability of the Ni0.4Mg0.6Fe2O4 electrode, which is observed to possess optimum properties, was ascertained in a saturated cryolite-alumina melt at the 960DGC, the operating temperature of aluminium electrolysis.