Low Temperature Synthesis of spinel-type Co x Fe 3-x O 4 (0 ≤ x ≤ 1.5) Oxide and its Application for Oxygen Evolution Electrocatalysis in Alkaline Solution

Spinel-type Fe 3 O 4 and its Co-substituted products were synthesized at 80°C by a co-precipitation method and investigated for their electrocatalytic properties in the form of oxide film electrode on Ni-support towards oxygen evolution reaction (OER) in alkaline medium. X-ray diffraction study indicated the formation of almost pure spinel ferrite phase with some impurities, which is found basically in the case of Co 0.5 Fe 2.5 O 4 oxide. The formation of spinel ferrite was also confirmed by recording the IR spectra. The cyclic voltammogram was carried out in the potential region 0.0 – 0.7 V and shows a pair of redox peaks; one an anodic (E Pa = 524±36) and corresponding cathodic (E Pc = 351±6) peak prior to the onset of oxygen evolution reaction. The anodic polarization study showed that the substitution of Co for Fe in the Fe3O4 lattice strongly affects the electrocatalytic properties of the materials. The optimum improvement in the activity is being with 1.0 mol Co-substitution. At E = 850 mV vs Hg/HgO/1M KOH (25±C), the current density with CoFe 2 O 4 (j = 315.6 mA cm -2 ) oxide was about 13 time higher than Fe 3 O 4. The Tafel slope values also decreased from 68 mV decade -1 to 44 mV decade-1 with Co-substitution. The thermodynamic parameters have been calculated for the oxide electrode, CoFe 2 O 4, at different potentials. It appears that as the potential is increased, the electrochemical standard enthalpy of activation (ΔH el °# ) of the oxide is decreased. SE-micrograph indicates that the substitution of Co for Fe decreases the crystallite size of the materials.