Synthesis of mesoporous NiCo2O4-rGO by a solvothermal method for charge storage applications

The spinel NiCo2O4 material has received considerable attention as an excellent supercapacitor material. In this study, we report a facile and cost-effective solvothermal method for the synthesis of mesoporous NiCo2O4 anchored on reduced graphene oxide (rGO). The electrochemical activity of the NiCo2O4-rGO and pristine NiCo2O4 materials were evaluated by cyclic voltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS). The NiCo2O4-rGO composite electrode shows a high specific capacitance value of 870 F g(-1) at a current density of 2 A g(-1) and it retains 600 F g(-1) capacitance even at a high current density of 20 A g(-1). Pristine NiCo2O4 shows a poor capacitance value of 315 F g(-1) at 2 A g(-1) and it retains only 191 F g(-1) at 10 A g(-1). Furthermore, the NiCo2O4-rGO nanocomposite shows an excellent cyclic performance with 90% capacitance retention even after 5000 charge-discharge cycles at a high current density of 4 A g(-1), whereas a pristine NiCo2O4 electrode shows only 45% capacitance retention. The high specific capacitance, remarkable rate capability and excellent cycling performance offered by the NiCo2O4-rGO composite is attributed to the high surface area and high conductivity. In addition, rGO is believed to shorten the diffusion, migration paths for electrolyte ions and an easy access for electrolyte ions into redox centers.