Abstract

The present study reports the synthesis and electrocatalytic evaluation of multi-metallic spinel oxides, NixFe1-xCo2O4 (x = 0, 0.3, 0.5, and 0.7), prepared via a co-precipitation method followed by annealing at 400°C. X-ray diffraction and Raman spectroscopy confirmed the formation of a spinel structure with a minor CoO impurity, with XPS revealing the presence of mixed-valence states (Co²?/Co³?, Fe²?/Fe³?, and Ni²?/Ni³?), indicative of complex redox chemistry. BET analysis showed mesoporous morphology, with the Ni0.5Fe0.5Co2O4 composition exhibiting the highest surface area (617.2 m²/g). Electrochemical measurements conducted in 0.1 M KOH demonstrated that all catalysts facilitated ORR through a dominant four-electron pathway. Among the compositions of NixFe1-xCo2O4 (x = 0, 0.3, 0.5, and 0.7) studied, Ni0.5Fe0.5Co2O4 displayed the best ORR activity with an onset potential of 0.75 V, half-wave potential of 0.62 V (vs. RHE), a limiting current density of ?2.82 mA/cm² and excellent cycling stability over 3000 cycles with minimal degradation. These highlight that an optimal Ni/Fe ratio in Co-based spinel oxide can synergistically enhance ORR kinetics and stability. The study provides new insights into how a minor CoO secondary phase and multivalent cations influence ORR activity, and underscores a novel, low-temperature route to tailor Ni0.5Fe0.5Co2O4 spinel oxide electrocatalysts for efficient oxygen reduction. © 2025 Elsevier B.V.