▎ 摘　　要

A 2 V asymmetric supercapacitor is developed using reduced graphene oxide-carbon nanofiber-MnCO3 nanocomposite (RGO-CNF-MnCO3) as positive electrode and RGO as negative electrode in a neutral 1 M Na2SO4 aqueous electrolyte. The RGO-CNF-MnCO3 composite positive electrode is prepared using hydrothermal method, and the X-ray diffraction (XRD) studies reveal the formation of crystalline rhodochrosite MnCO3 in the as-prepared nanocomposites. The electron microscopic images show the formation of MnCO3 nanoparticles on RGO-CNF surface in the nanocomposites. Fourier transform infrared (FT-IR) and Raman spectroscopic analyses confirm the existence of various functional groups in RGO-CNF-MnCO3 nanocomposite. RGO is prepared using modified Hummers and Offeman's method. Cyclic voltammetry and galvanostatic charge-discharge experiments of symmetric RGO-CNF-MnCO3 and RGO cells show a poor energy density of 4.8 and 3.6 Wh/kg at 0.1 A/g, respectively. Cyclic voltammetry and galvanostatic charge-discharge experiments of asymmetric RGO//RGO-CNF-MnCO3 cell in aqueous 1 M Na2SO4 solution show the stability of asymmetric cell up to 2 V with a high energy density of 21 Wh/kg. The RGO//RGO-CNF-MnCO3 asymmetric cell shows excellent capacitance retention of 97 % even after 1000 cycles charge-discharge at 1 A/g. In addition, a high energy density of 15 Wh/kg is retained when the power density increases to 1.07 kW/kg for the asymmetric cell. The high energy density and stability of prepared asymmetric RGO//RGO-CNF-MnCO3 cell is promising for electrochemical energy storage in aqueous electrolyte.