Kinetic and Thermodynamic Insights into Oxygen Evolution Reaction on Defect-Engineered Metal Oxide Nanocatalysts

Developing sustainable hydrogen production from water electrolysis is an important topic in which the design of earth-abundant, high-performance electrocatalysts for the oxygen evolution reaction (OER) remains a central challenge. We have synthesized oxygen vacancy-enriched iron–nickel composite oxide nanocatalysts Ov-Fe₂O₃/NiO from Iraqi natural hematite sourced from Derbendikhan district of Sulaymaniyah. In this work, we report. The preparation of catalysts occurred via alkaline co-precipitation and following hydrothermal crystallisation and thermal annealing in dilute H₂/Ar. Using X-ray diffraction (XRD), BET surface area, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and electron paramagnetic resonance (EPR) characterisation the oxygen vacancy defects were confirmed to be introduced in the material and a successful hetero-structure with a surface area of 78.3 m² g⁻¹ (crystallite size 12.4 nm).
 In alkaline electrolyte (1 M KOH), the Ov-Fe₂O₃/NiO composite achieved an overpotential of 285 mV at a standard 10 mA cm⁻² current density, a Tafel slope of 48 mV dec⁻¹, and a charge-transfer resistance of 3.2 Ω, which are all significantly superior to those of the undoped composite, single-phase oxides, and the reference IrO₂ catalyst. The scientists conducted electrochemical measurements of the selected nickel catalyst at 298–338 K. This enabled them to carry out rigorous kinetic analysis using the Arrhenius and Eyring formalism. The analysis yielded an activation energy of 28.4 kJ mol⁻¹, an enthalpy of activation of 25.9 kJ mol⁻¹, and an entropy of activation of −48.3 J mol⁻¹ K⁻¹ for the defect-engineered catalyst. The above values reflect lower barriers relative to those of the reference materials. Based on findings related to density of states reasons and XPS analysis, these thermodynamic characteristics suggest that the presence of oxygen vacancies boosts the adsorption of reactive oxygen intermediates while improving the efficiency of charge carriers and reducing O–O bond intrinsic kinetic barriers. This research provides a way to quantify designed structural defects in relation to the thermodynamic landscape of OER catalysis and shows that locally sourced Iraqi mineral precursors can serve as a feedstock for advanced manufactured electrocatalysts.