Synthesis, physicochemical and electrochemical properties of nickel ferrite spinels obtained by hydrothermal method for the Oxygen Evolution Reaction (OER)

The electrocatalysis of oxygen evolution reaction (OER) has been studied at the face centered cubic (FCC) Ni_xFe_3-xO₄ (0 ≤ x ≤ 1.0) anodes in 1M KOH solutions at 25 °C. These oxides were synthesized by the hydrothermal method and reproduced in the form of film on a nickel support by an oxide-slurry painting technique. The effect of Ni substitution in the base oxide (Fe₃O₄) was investigated with regards to morphology, structure and catalytic performance by using techniques, such as, scanning electron microscopy (SEM), infrared (IR), X-ray diffraction (XRD), cyclic voltammetry (CV), Tafel polarization, and electrochemical impedance spectroscopy (EIS). Among synthesized oxides, the NiFe2O4 electrode was found to be the most active anode for oxygen evolution (OE). Tafel slope values (b = 41±6 mV decade^-1) were approximately the same for each electrocatalyst in spite of the amount of the Ni-metal being doped and the order for the OER with respect to OH^- concentration were found to be ~ 2. The electrocatalytic activities of the electrodes are correlated with their surface roughness. Based on the electrode kinetic results, mechanism of the oxygen evolution is suggested.