Co/Co3O4 nanoparticles embedded into thin O-doped graphitic layer as bifunctional oxygen electrocatalysts for Zn-air batteries

Abstract

Developing low-cost and efficient oxygen electrocatalysts for oxygen reduction and evolution reaction (ORR&OER) is critical for various energy conversion technologies. Herein, we report an arc discharge strategy coupled with an controllable oxidation to prepare Co/Co3O4 nanoparticles confined in ultrathin O-doped graphitic carbon layer (Co/Co3O4@ODGC) as highly active bifunctional oxygen electrocatalysts for Zn-air batteries (ZABs). The resultant Co/Co3O4@ODGC shows an impressive ORR performance with a half-wave potential of 0.80 V in 0.1 M KOH. It also exhibits remarkable OER performance with a small overpotential of 300 mV to reach a current density of 10 mA cm−2. Both experimental studies and theoretical calculations indicate that the high ORR and OER activities are attributed to the synergistic electronic effect between the Co/Co3O4 heterostructures and ultrathin O-doped graphitic layer (~1.5 nm). Particularly, the electron redistribution in graphitic layer caused by O-doping and carbon defects significantly decreases the energy barrier for oxygen adsorption/desorption. More attractively, the as-constructed ZABs with Co/Co3O4@ODGC cathode show an impressive open voltage (1.60 V), a high power density of 107 mW cm−2, and good stability without nearly no performance decay for 40 h at 2.0 mA cm−2. This work provides both fundamental understanding and easy strategy for developing the efficient bifunctional oxygen electrocatalysts for high performance metal-air batteries.