Controlled Synthesis of Novel NiCo₂O₄–Co_1–<i>x</i>Cr_<i>x</i>Fe₂O₄ (0 ≤ <i>x</i> ≤ 0.8) Composites for Electrolytic Oxygen Evolution and Methanol Oxidation in Alkaline Medium

The electrochemical performance of spinel oxide-spinel oxide composites [NiCo2O4–Co1–xCrxFe2O4 (0 ≤ x ≤ 0.8)] for the oxygen evolution reaction (OER) and methanol oxidation reaction (MOR) has been investigated. Materials were obtained by utilizing coprecipitation and sol–gel techniques. Fourier-transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) studies revealed the existence of nearly pure spinel phase composite materials. The valence distribution of the materials was assessed via X-ray photoelectron spectroscopy (XPS). The particle size of the materials was determined using transmission electron microscopy (TEM). The morphological analysis of the materials was performed using scanning electron microscopy (SEM). Electrochemical investigations like cyclic voltammetry (CV) and Tafel experiment were performed in KOH solution as well as KOH and CH3OH solution at 25 °C. Anodic polarization curves were used to determine the electrocatalytic performance of the materials and NiCo2O4–CoFe2O4 was observed to be most active toward the OER (j = 129.9 mAcm–2) and MOR (j = 138.2 mAcm–2) at a potential of 750 mV. The stability of the electrodes was examined via chronoamperometric experiments and further perception of the increment of electrocatalytic activity was acquired through the electrochemical active surface area (ECSA) assessments by means of electrochemical impedance spectroscopy (EIS). Thermodynamic parameters like standard electrochemical energy of activation (ΔHel°#), standard enthalpy of activation (ΔH°#), and standard entropy of activation (ΔS°#) were analyzed via capturing Tafel plot at various temperatures in KOH solution as well as KOH and CH3OH solution.