Evolution of physicochemical and electrocatalytic properties of NiCo2O4 (AB2O4) spinel oxide with the effect of Fe substitution at the A site leading to efficient anodic O2 evolution in an alkaline environment

Within the framework of this work, spinel-type ternary transition metal oxides of nickel, cobalt and iron with the composition Fe_xNi_1−xCo₂O₄ (0 ≤ x ≤ 1) were prepared and tested as promising electrocatalysts for the oxygen evolution reaction (OER) in alkaline water electrolysis. The hydroxide precipitation method was used for the synthesis. The morphology, structure and specific surface area of the prepared electrocatalysts were determined by means of scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, the Brunauer Emmet Teller method and X-ray photo electron spectroscopy. The electrochemical properties were tested by thin-film technique on a rotating disk electrode and in a single-cell laboratory water electrolyzer coupled with electrochemical impedance spectroscopy. The OER studies indicate that substitution of Ni by Fe increases the electrocatalytic activity of the resulting material significantly. The highest activity was achieved for x = 0.1. Whereas the current density obtained using a pure nickel anode in the water electrolysis test was 54 mA cm⁻² at a cell voltage of 1.85 V, in the case of the anode modified with NiCo₂O₄ catalyst the value was 87 mA cm⁻². Using ternary transition metal oxides in the water electrolysis test and under identical conditions, the catalyst with the highest activity displayed a current density of 115 mA cm⁻².