Sonochemical assisted synthesis MnO₂/RGO nanohybrid as effective electrode material for supercapacitor

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 -1.1V 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 0.5M sodium sulfate in the potential window of 0.0-1.0V. The electrochemical investigations reveal that MnO₂/RGO exhibits high specific capacitance (C_s) of 375Fg^-1 at current density of 1Ag^-1 and good cycle stability (93% capacitance retention after 500 cycles at a scan rate of 200mVs^-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.