Nitrogen doped graphene quantum dots (N-GQDs)/Co3O4 composite material as an efficient bi-functional electrocatalyst for oxygen evolution and oxygen reduction reactions

In this work, a facile development of a bi-functional electrocatalyst for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is reported. A composite material comprising of tiny particles of nitrogen doped graphene quantum dots (N-GQDs) embedded into cobalt oxide (Co3O4) flakes is prepared by sodium borohydride reduction method and followed by annealing at 600 °C under inert atmosphere. Structural, morphological and crystalline features are analyzed using FESEM, TEM, HRTEM, XRD and XPS studies. Moreover, optical and fluorescence properties of N-GQDs are studied using UV–visible and fluorescence spectroscopic techniques. These studies clearly reveal and confirm the formation of a composite material. Further electrochemical characteristics toward OER and ORR are investigated by using linear sweep voltammetry (LSV) and cyclic voltammetry (CV) techniques. Compared to the individual entities of pure Co3O4 and N-GQDs alone, the electrocatalytic activity of N-GQDs/Co3O4 composite material is significantly higher towards ORR. Similarly, the same composite material is also used as an electrocatalyst for OER in 0.1 M KOH aqueous electrolyte and it exhibits a lower overpotential of 330 mV to obtain a current density of 10 mA/cm2 along with higher electrocatalytic activity and the reason is mainly attributed to the synergistic effect between N-GQDs and Co3O4. Thus, N-GQDs/Co3O4 composite material is demonstrated to be a high performance bi-functional electrocatalyst for ORR and OER.