Effect of Co-substitution on the electrocatalytic properties of Ni1.5Fe1.5O4 for oxygen evolution in alkaline solutions

Abstract

Some ternary ferrites having composition CoxNi1.5-xFe1.5O4 (0.0 ≤ x ≤ 1.25) have been synthesized by NH4OH co-precipitation method at 11.5 pH. Materials, so obtained, were tested for their electrocatalytic properties towards oxygen evolution reaction (OER) in the form film on Ni-support in alkaline solution. The study showed that the electrocatalytic properties the material increased with partial substitution of Co for Ni in the base oxide (Ni1.5Fe1.5O4). The value being highest with 0.5 mol Co-substitution. At E = 850 mV vs Hg/HgO in 1M KOH at 25 ºC, the electrode showed apparent current density 206.2 mA cm-2, which is about 3 times higher than the base oxide. The Tafel slope values were ranged between 46-82 mV decade-1. A pair of redox peak, an anodic (EPa = 522±28 mV) and corresponding cathodic (EPc= 356±9 mV), was observed in the cyclic voltammetry (CV) study of the material. The thermodynamic parameters namely, standard apparent electrochemical enthalpy of activation ( ), standard enthalpy of activation ( ) and standard entropy of activation ( ) for the oxygen evolution reaction (OER) have also been determined by recording anodic polarization curve in 1M KOH. The value of was observed to be almost similar with each oxide electrode. The values were highly negative and ranged between ~ -165 and ~ -207 J deg-1 mol-1. Phase and morphology of materials have been investigated by using physical techniques X-ray diffraction, infrared spectroscopy (IR) and scanning electron microscope (SEM), respectively.