Augmented and sustained oxygen reduction reaction activity of NiCo2O4 by the incorporation of Ag

Abstract

Developing a highly efficient and durable electro-catalyst for the oxygen reduction reaction (ORR) has received substantial attention for clean energy devices, including direct methanol fuel cells (DMFCs). Spinel structures such as NiCo₂O₄ tend to exhibit remarkable ORR activity. In this work, Ag-NiCo₂O₄ has been successfully synthesized via a solvothermal process combined with a solid-state reaction followed by thermal treatment to improve the activity of NiCo₂O₄ further. Ag-NiCo₂O₄ possesses a comparable ORR activity, higher stability, and excellent methanol tolerance with respect to the state-of-the-art catalyst Pt/C in alkaline media. It exhibited an onset potential of 0.82 V and a diffusion-limited current of −5.0 mA cm⁻² @1800 rpm, superior to the NiCo₂O₄ and Ag/C catalysts. The ORR catalyzed on Ag-NiCo₂O₄ proceeded via a 4e⁻ reduction pathway with minimal generation of peroxide intermediate. The intensified ORR performance of Ag-NiCo₂O₄ is ascribed to the synergistic effect of Ag nanoparticles and the spinel NiCo₂O₄.