Effect of Co-substitution on the Electrocatalytic Properties of Ni1.5Fe1.5O4 for Oxygen Evolution in Alkaline Solutions

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 1.25 mol Co-substitution. At E = 850 mV vs Hg/HgO in 1M KOH at 25 degrees C, the electrode showed apparent current density 137.1 mA cm(-2), which is about 2.5 times higher than the base oxide. The Tafel slope values were ranged between 53-90 mV decade-1. A pair of redox peak, an anodic (E-Pa = 522 +/- 28 mV) and corresponding cathodic (E-Pc= 356 +/- 9 mV), was observed in the cyclic voltammetry (CV) study of the material. The thermodynamic parameters namely, standard apparent electrochemical enthalpy of activation (Delta H-el degrees(not equal)), standard enthalpy of activation (Delta H degrees(not equal)) and standard entropy of activation (Delta s degrees(not equal)) for the oxygen evolution reaction (OER) have also been determined by recording anodic polarization curve in 1M KOH. The value of Delta H degrees(not equal) was observed to be almost similar with each oxide electrode. The Delta s degrees(not equal) values were highly negative and ranged between similar to -165 and similar to -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.