Co–Co3O4 nanostructure with nitrogen-doped carbon as bifunctional catalyst for oxygen electrocatalysis

In view of the development of advanced bi-functional oxygen electrodes for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), herein, we report the synthesis of Co–Co3O4 nanostructure encased in N-doped carbon (Co–Co3O4/NC) by carbothermal reduction followed by controlled oxidative treatment. The formation of a protective-active oxide layer on the metallic-Co not only facilitated the effective charge separation and transport but also displayed improved stability of Co–Co3O4/NC in an alkaline operating condition. The Co–Co3O4/NC catalyst afforded 0.810 V overvoltage between ORR and OER in 0.1 M KOH solution, consequently, this lower reversible overvoltage would result in energy saving of around 0.246 V if Co–Co3O4/NC is used as an oxygen electrode instead of commercially available 40 wt % Pt/C. Furthermore, in comparison with the use of Pt/C + IrO2 as an ORR and OER catalyst, respectively the single bi-functional electrocatalyst i.e., Co–Co3O4/NC would result in energy saving of around 0.13 V.