Graphene/MnO2-based composites reduced via different chemical agents for supercapacitors

Graphene/MnO2 composites are synthesized by the chemical reduction of GO/MnO2 using both hydrazine hydrate (H-RGO/MnO2) and sodium borohydride (S-RGO/MnO2) as reducing agents. The morphology and microstructure of the as-prepared composites are characterized by X-ray diffractometry, field-emission scanning electron microscopy, Raman microscopy, thermogravimetric analysis and X-ray photoelectron spectroscopy. Characterizations indicate that MnO2 is successfully formed on the GO surface and GO is reduced successfully by using both hydrazine hydrate and sodium borohydride as reducing agents. H-RGO/MnO2 shows higher electrical conductivity than that of S-RGO/MnO2 since it has a lower concentration of oxygen-containing functional groups. The capacitive properties of the H-RGO/MnO2 and S-RGO/MnO2 electrodes are measured using cyclic voltammetry and galvanostatic charge/discharge tests and electrochemical impedance spectroscopy in a three-electrode experimental setup using a 1 M Na2SO4 aqueous solution as the electrolyte. The H-RGO/MnO2 electrode displays a specific capacitance as high as 327.5 F g−1 at 10 mV s−1, which is higher than that of the S-RGO/MnO2 electrode (278.6 F g−1). It is anticipate that the formation of nanoneedle structures of MnO2 on graphene oxide surfaces after the hydrazine reduction procedure is a promising fabrication method for supercapacitor electrodes.