Synthesis of Ultrasmall NiCo2O4 Nanoparticle-Decorated N-Doped Graphene Nanosheets as an Effective Catalyst for Zn-Air Batteries

Developing oxygen electrocatalysts with outstanding activity and low cost is vital to the promotion of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) of Zn-air batteries. Herein, an NiCo2O4 nanoparticle-decorated nitrogen-doped graphene nanosheet (NiCo2O4/N-G) is synthesized as a bifunctional electrocatalyst. The ultrasmall NiCo2O4 nanoparticle with an average particle size of 4 nm can introduce plentiful reaction active sites. Furthermore, the N-G nanosheets with small dimensions of 200 nm possess an extremely large specific surface area and can effectively restrict the aggregation of NiCo2O4 nanoparticles and promote species transport. Compared with NiCo2O4 and N-G, NiCo2O4/N-G exhibits a higher ORR and OER electrocatalytic activity in alkaline electrolytes, and it demonstrates almost comparable ORR activity but superior stability to commercial Pt/C. Using the NiCo2O4/N-G catalyst, a home-built Zn-air battery demonstrates a peak power density of 108.3 mW cm(-2), an excellent discharge capacity of up to 792.6 mAh g(Zn)(-1), and a superior energy density of up to 879.9 Wh kg. Moreover, stable charge-discharge voltage gaps and an energy efficiency of similar to 63% at 10 mA cm(-2) can sustain for over 540 cycles during cycling, indicating excellent cycling stability.

Automated summary

In this study, a NiCo2O4 nanoparticle-decorated nitrogen-doped graphene nanosheet (NiCo2O4/N-G) bifunctional electrocatalyst was synthesized, showing excellent ORR and OER activity with superior stability through stable charge-discharge cycling.