Hydrothermal Synthesis Of3D-rGO Supported MnO₂Composites And Its Electrochemical Properties

In twenty-first Century, the sustainable development of society has become the commongoal of the human society, and it has also been concerned by the society. Renewable greenenergy will gradually become the main body of social energy supply.The development ofthe energy storage device is considered as a strategic technology for the development ofrenewable energy, and has been widely concerned by governments and enterprises.In recent years, supercapacitors as a advanced power storage device received widespreadattention through the word. The performance of supercapacitor is mostly determined by theelectrode materials, among which graphene and manganese dioxide have actively studiedbecause of their excellent physical and chemical performance. Unlike common dispersegraphene, three-dimensional structured graphene has more outstanding electron transportproperties, large specific surface area and three-dimensional cross-linked porous structure,and becomes the focus of researches in carbon materials and supercapacitors.In this paper, we designed two hydrothermal routines to prepare three-dimensionalstructured reduced graphene oxide/manganese dioxide (3D-rGO/MnO2) composites,directly as a free-binder and free-standing electrochemical electrode. For this compositeelectrode, various techniques including X-ray diffraction (XRD), X-ray photoelectronspectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), differential thermalanalysis (TG), scanning electron microscopy (SEM) and transmission electron microscopy(TEM) were employed to characterize the phases and microstructures, electrochemicaltests such as cyclic voltammetry, AC impedance, constant current charge discharge andcyclic stability were used to analyzed the electrochemical properties.In routine Ι (two-step routine),3D-rGO/MnO2was obtained by firstly VC reducing GOgiving3D-rGO, followed by immersing3D-rGO in KMnO4solution. By varying the rationof rGO to KMnO4, the MnO2loading fraction in3D-rGO can be easily adjusted. The resltsshow, under a scan rate of1A/g, the specific capacitance of3D-rGO/MnO2composite canreach308F/g, and the corresponding retention rate is with90.2%after500cycles.In routine ΙI(one-step routine),3D-rGO/MnO2was obtained by direct hydrothermal reaction of GO and Mn2+at135℃for12h, in which the MnO2loading fraction in3D-rGOwas controlled by the ration of rGO to Mn2+. Under a scan rate of1A/g, the specificcapacitance of3D-rGO/MnO2composite reaches406F/g, and the retention rate is with92%after1000cycles.