Synthesis and electrochemical properties of hollow-porous MnO2-graphene micro-nano spheres for supercapacitor applications

Hollow-porous MnO2-graphene (GR) micro-nano spheres for supercapacitors were synthesized via a simple, quick and cost-effective strategy at room temperature. The crystal structure and morphology of the as-prepared materials were investigated by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and nitrogen adsorption–desorption. The experimental results showed that the obtained pure MnO2 and MnO2-GR composite has a typical birnessite-type MnO2 structure with hollow-porous micro-nano spheres morphology. Furthermore, the electrochemical properties of the as-prepared samples were examined using cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) and electrochemical impedance spectroscopy (EIS). Surprisingly, the hollow-porous MnO2-5 wt.% GR micro-nano sphere displays a high specific capacitance (256.8 F g− 1 at 150 mA g− 1), excellent cycling stability, smaller equivalent series resistance and charge transfer resistance. The superior capacitive performance is related to its unique structure and poor crystallinity. Therefore, the hollow-porous MnO2-GR micro-nano sphere can be promising electrode materials for supercapacitors with enhanced properties.