Manganese dioxide (MnO2) needle-like nanostructures are successfully synthesized by a sonochemical method from an aqueous solution of potassium bromate and manganese sulfate. Also, hybride of MnO2 nanoparticles wrapped with graphene oxide (GO) nanosheets are fabricated through an electrostatic coprecipitation procedure. With adjusting pH at 3.5, positive and negative charges are created on MnO2 and on GO, respectively which can electrostatically attract to each other and coprecipitate. Then, MnO2/GO pasted on stainless steel mesh is electrochemically reduced by applying −1.1 V to obtain MnO2/RGO nanohybrid. The structure and morphology of the MnO2 and MnO2/RGO nanohybrid are examined by Raman spectroscopy, X-ray diffraction (XRD), atomic force microscopy (AFM), field emission-scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDX), and thermal gravimetric analysis (TGA). The capacitive behaviors of MnO2 and MnO2/RGO active materials on stainless steel meshes are investigated by cyclic voltammetry (CV), galvanostatic charge/discharge test and electrochemical impedance spectroscopy (EIS) by a three-electrode experimental setup in an aqueous solution of 0.5 M sodium sulfate in the potential window of 0.0–1.0 V. The electrochemical investigations reveal that MnO2/RGO exhibits high specific capacitance (Cs) of 375 F g−1 at current density of 1 A g−1 and good cycle stability (93% capacitance retention after 500 cycles at a scan rate of 200 mV s−1). The obtained results give good prospect about the application of electrostatic coprecipitation method to prepare graphene/metal oxides nanohybrids as effective electrode materials for supercapacitors.
