The Preparation Of Graphene/Transition Metal Oxides Composites And Their Application In Supercapacitors

In this thesis,graphene/transition metal oxide compositesincluding NiO/graphene,MoO3/graphene,and MnO2/graphene were prepared by different methods.These composites coud be applied in supercapacitors as electrode materials,and the capacitive properties were investigated.The resulting productswere characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FT-IR),X-ray photoelectron spectroscopic analysis(XPS),thermogravimetry(TG),and Brunauer-Emmett-Teller(BET).The electrochemical properties of these composites were also studied.The main contents of the thesis are summarized as follows:1.NiO/graphene nanocomposites have been successfully synthesized by a facile hydrothermal method followed by a calcination process.When Graphene oxide(GO)precursorwas handled with vacuumfreeze-drying process,the as-prepared nanocomposite appeared a perfect flowerlike structure.On the contrary,the final corresponding composite presented a polyhedral structure.The formation mechanism of the two nanocomposites with different morphologies has been studied.The prepared NiO/graphene nanocomposites with different shapes can be used for supercapacitor electrode materials.Through electrochemical tests,the flowerlike NiO/graphene composite shows better supercapacitive performances than that of the polyhedral one.It shows a specific capacitance as high as 500 Fg' at a scan rate of 5 mVs-1 in 1 M KOH electrolyte and excellent long-term cycle stability after 1000 cycles charge-discharge cycleat a current density of 1 Ag-1.2.Novel nano flake-like and nanobelt-like ?-MoO3/graphene nanocomposites were synthesized by a facile hydrothermal method through tailoring the content of Mo source,respectively.The formation mechanisms of ?-MoO3/graphene nanocomposites with different morphologies had been investigated.As a model,the ?-MoO3/graphenenanocomposites were studied for electrochemical energy storage supercapacitor devices.The results showed that ?-MoO3 nanoflakes/graphene possessed better supercapacitive performances than that of ?-MoO3 nanobelts/graphene,arising from the structural superiority and optimum compositions.It exhibited a high specific capacitance(up to 360 Fg-1)at a current density of 0.2 Ag-1,good rate capability,and a nearly 100%long-term cycle stability.3.Ni fiber with a diameter about 0.15 mm was decorated by rGO and MnO2 via one-step electrochemical deposition method.The single rGO/MnO2/Ni fiber electrode showed highareal specific capacitance of 119.4 mFcm-2 at a current density of 0.5 mAcm-2 in 1 M Na2SO4.The rGO/MnO2/Ni fiber electrodes were assembled into freestanding,flexible,lightweight,fiber-shaped symmetrical fiber-based micro-supercapacitor devices with PVA/LiClgelsolid stateelectrolyte,which showed a maximum areal capacitance value of 26.9 mFcm-2.Moreover,the symmetrical supercapacitor demonstrated good flexibility and cyclic stability.This research provided a simple,facile,and low-costmethod for flexible,lightweight,high-performancewearableenergy conversion and storage micro-devices.