Evaluation of Mg 2+-substituted NiFe 2O 4 as a green anode material

Abstract

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 CO 2, CO, and CF 6, during electrolysis. In this regard, the noncarbon anode material Ni 1−xMg xFe 2O 4 ( 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 Mg 2+ 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 Mg 2+ 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 Mg 2+ 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 ( R f) and the Double layer capacitance ( C dl) of the synthesized electrodes were measured by using Electrochemical Impedance Spectroscopy. The chemical stability of the Ni 0.4Mg 0.6Fe 2O 4 electrode, which is observed to possess optimum properties, was ascertained in a saturated cryolite–alumina melt at the 960 °C, the operating temperature of aluminium electrolysis.