Core–shell reduced graphene oxide/MnOx@carbon hollow nanospheres for high performance supercapacitor electrodes

Abstract

We demonstrate a novel and efficient approach to fabricate reduced graphene oxide (RGO)/MnOx@carbon hollow nanospheres (HCNs) nanohybrids for high performance supercapacitor application. Mn2+ ions can bind with negatively charged O atoms on graphene oxide (GO) via electrostatic forces to generate RGO/MnOx (x⩽2) under hydrothermal condition. This process was utilized to grow MnOx layers on the surfaces of RGO, and the RGO/MnOx was encapsulated within the outer carbon shell to obtain RGO/MnOx@HCNs. RGO/MnOx@HCNs have a regular hollow structure with uniform outer shells (∼10nm) and inner spherical pores (∼150nm), high surface areas (493–668m2g−1), and high contents of MnO2 (12.2–19.6wt%). As-designed ternary core–shell 3D nanoarchitecture prevents the leaching of loaded manganese oxides and avoids the aggregation of RGO within the carbon shell, which effectively guarantees the electrochemical activity of each electroactive components. Consequently, a typical RGO/MnOx@HCNs as a supercapacitor electrode exhibits a high specific capacitance (355 and 270Fg−1 in a three-electrode and two-electrode system at 1.0Ag−1, respectively) in 6M KOH electrolyte. Besides, the electrode shows a high rate charge–discharge capability (20.0Ag−1), and good electrochemical stability (88% capacitance retention after 5000 cycles at 0.5Ag−1). The results suggest that the core–shell RGO/MnOx@HCNs nanostructures provide promising prospects for electrochemical energy storage applications.