The Synthesis Of Graphene-based Composites、 Urchin-like MnO₂via A Hydrothermal Method And Their Application In Supercapacitors

In this thesis, different supercapacitor electrode materials were prepared by a hydrothermalmethod, including graphene/conductive polymer composites, graphene/metal oxide composites andpure metal oxide nanomaterials. The morphology, structure, and composition of the products wereexamined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-rayphotoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR).The electrochemical properties of these nanocomposite materials were also studied. The maincontents of the thesis are summarized as follows:1, A ternary nanocomposite of graphene/polyaniline (PANI)/porous silica MCM-41(MCM-41)was prepared by hydrothermal method. The different amount of graphene oxide (GO) ingraphene/PANI/MCM-41nanocomposites had strong effect on the supercapacitor performance. Theexperimental results showed that the specific capacitance of graphene/PANI/MCM-41could reachthe highest value when the GO content was50%. The specific capacitance of the nanocompositewas405F g-1at a current density of0.8A g-1. Furthermore, over91.4%of the original capacitancewas retained after repeating the galvanostatic charge-discharge for1000cycles. The performance ofthe prepared supercapacitor by different content of GO were studied in detail.2, The novel MnO2petal nanosheet and nanorod/graphene composite are successfully fabricatedby a facile one-step hydrothermal method through changing the content of Mn source. Theformation mechanism of different morphologies MnO2/graphene composites have been studied. Thestructure of MnO2/graphene is like to sandwich, which MnO2petal nanosheets and nanorod arehomogeneously anchored on each side of graphene. Furthermore, the MnO2/graphene compsiteswith different shapes can be used to supercapacitor electorde materials. The experimental resultsshow that the MnO2petal nanosheet/graphene composite has better capacitance performance thanthat of the MnO2nanorod/graphene composite. The MnO2petal nanosheet/graphene compositeshows the excellent specifc capacitance as high as516.8F g-1at a scan rate of1mV s-1in1MNa2SO4electrolyte and good long-term cycle stability, indicating its potential application to act as apromising electrode material for high-performance supercapacitors. This study provides a facile andin situ method to prepare metal oxide/graphene composite materials and a novel scaffold toconstruct other metal oxide with graphene for energy storage.3, In this part, we described a simple hydrothermal method to synthesize hollow urchin-like manganese dioxide without template and surfactant.3D Hollow urchin-like manganese dioxide wasconsisted of single manganese dioxide hollow tube with stable structure. The nano-material exhibitsexcellent stability and capacitive, as high as254.6F g-1in1M Na2SO4electrolyte at a scan rate of1mV s-1, and over97.5%of the first cycle capacitance was retained after repeating the galvanostaticcharge-discharge for1000cycles, indicating its potential application to act as a promising electrodematerial for supercapacitors.