Hierarchical NiCo2O4 hollow nanospheres as high efficient bi-functional catalysts for oxygen reduction and evolution reactions

• Hierarchical NiCo2O4 hollow nanospheres have been prepared via a hard template method.
• The synthesized NCO hollow consists of ultrathin nanosheets.
• The NCO hollow exhibits excellent catalytic activity for both ORR and OER.
• The NCO hollow also owns superior long-term stability.

High efficient, cost-effective catalysts for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are the key issue of the rechargeable lithium-air batteries. Herein, we report the facile synthesis of hierarchical NiCo2O4 (NCO) hollow nanospheres via a hard template method and following heat treatment. The synthesized hollow NCO consists of ultrathin nanosheets, which could provide larger specific surface area, more active sites and easy access channels for oxygen and electrolyte transport. The electrochemical studies reveal that the NCO hollow owns excellent ORR and OER catalytic activities, characterized with lower onset potential, higher diffusion limiting current density. Moreover, the NCO hollow shows superior stability compared to that of NCO urchin, Pt/C and RuO2 for ORR and OER, respectively. The excellent electrocatalytic activities, long-term stability for both the ORR and OER and the facile synthesis procedure make the NCO hollow a potential promising bi-functional catalyst for the metal-air batteries and fuel cells.