Evaluation of a ZnO–NiO/rGO hybrid electrocatalyst for enhanced oxygen reduction reaction (ORR) applications

Abstract

The development of oxygen reduction reaction (ORR) catalyst that are affordable and long-lasting is crucial for the expansion of energy conversion applications. In this study, we synthesized a ZnO–NiO/reduced graphene oxide hybrid electrocatalyst by using the co-precipitation method. X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Brunauer–Emmett–Teller (BET) analysis were used to characterize the synthesized ZnO–NiO/rGO hybrid catalyst. The XRD analysis showed that ZnO had a wurtzite structure, whereas the phase of NiO had a cubic structure. The TGA and BET investigations of the hybrid catalyst revealed its excellent thermal stability and large specific area (395.8 m² g⁻¹) compared to bare catalysts. Through transmission electron microscopy (TEM) analysis, we observed that ZnO nanorods and NiO nanoparticles are distributed evenly on the rGO surface. The electrochemical analysis showed that the ZnO–NiO/rGO hybrid catalyst had highly efficient catalytic activity for the ORR. It had a high limiting current density (7.1 mA cm⁻²), a positive onset potential (0.95 V), a low rate of H₂O₂ formation (less than 15%), and long-term stability. The oxygen reduction process on the ZnO–NiO/rGO hybrid catalyst was demonstrated to occur via a highly efficient 4e⁻ mechanism using rotating ring-disk and rotating disk electrode investigations. The ZnO–NiO/rGO hybrid catalyst demonstrated significant promise as an expensive metal-free catalyst for alkaline fuel cell cathodes.