Self-template synthesis of hollow flower-like NiCo₂O₄ nanoparticles as an efficient bifunctional catalyst for oxygen reduction and oxygen evolution in alkaline media

Abstract

A method was proposed to synthesize hollow flower-like NiCo2O4 composed of porous nanosheets using a self-template approach. The unique structure is attributed to the synergistic effect of the Kirkendall effect and the Ostwald ripening mechanism. The sheet-like and porous structure endowed the material with a specific surface area of 137.1 m2 g−1 and a pore volume of 0.418 cm3 g−1. The distinctive structure and high-density active sites imparted excellent catalytic performance in oxygen reduction (ORR) and oxygen evolution (OER) reactions. Electrochemical tests showed that the limit current density of ORR reached 5.58 mA cm−2, comparable to that of the noble metal Pt/C (20 wt%). The overpotential of OER at a current density of 10 mA cm−2 was only 380 mV, significantly lower than that of the noble metal RuO2. These results indicate that the synthesized hollow flower-like NiCo2O4 has the potential to replace noble metals in ORR and OER catalytic applications.