Evaluation of Mg~(2+)-substituted NiFe_2O_4 as a green anode material

摘要

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-x)Mg_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_(0.4)Mg_(0.6)Fe_2O_4 electrode, which is observed to possess optimum properties, was ascertained in a saturated cryolite-alumina melt at the 960 deg C, the operating temperature of aluminium electrolysis.