| Due to the large surface area, small size and other characteristics, nanomaterials have their particularity in quantum effects, price effects, quantum size effects and dielectric confinement effects. That’s why nanomaterials have important applications in energy conversion and storage and so on. The rational design and synthesis of diverse nano-structures and performance optimization of novel nanomaterials are the main trends of the continuous development of current material science and human society, expanding an important development direction in the field of energy and the environment applications. Heterostructural nanocomposites are a new class of hybrid nanomaterials, in which different component or functional compositions are uniformly and controllably assembled in different space but in one unit. They not only have the properties of the single component in namomaterials, but also possess some new functional effects due to the heterojunction of each single nanomaterial. Advantages of the nanocomposites expand their applications in a wide range of fields including energy conversion and storage, sensors, catalysis, biology and medicine and so on.Nowadays, more and more attention is paid on the research of the energy technology. In order to fulfill the requirements of the current energy storage system, to provide the electrochemical energy storage devices with high energy density at high power demands and low cost, such as lithium ion batteries or supercapacitors, is also a great challenge. So far, many heterogeneous nanostructured materials have been studied with multi-functionalization. One of the major challenges is how to design and fabricate creative nanomaterials with multifunction and excellent performance.This thesis focuses on the synthesis, property study and application of nanomaterials due to the demand of practical applications. This work mainly includes the following aspects:(1) Rational designation of nanocomposites based on the transitional metal oxide tin oxides, and the exploration of its application in lithium ion batteries; (2) Modification of mesoporous titania and device fabrication for the use of anode materials; (3) New device fabrication and exploration of photoelectric conversion for energy storage system.In Chapter 2, we fabricate the tin oxide nanosheets using a facile hydrothermal method. The structure changes from 2-D to 3-D through self-assembly method. Such nanomaterials have many advantages including short lithium ion transport path, and high surface area. As lithium ion battery anode materials,3-D flower-like tin oxide namosheets exhibit excellent electrochemical performance.In Chapter 3, We synthesize a new hierarchical SnO2/Fe2O3 heterostructure, consisting of a micron-sized primary SnO2 nanosheet base and sub-10 nm diameter Fe2O3 nanorod branches grown on the nanosheet surface, using a facile, two-step hydrothermal growth method. The two-dimensional SnO2 nanosheets offer a high surface area and fast charge transport pathways, and the one-dimensional α-Fe2O3 nanorods serve as structural spacers between individual SnO2 nanosheets, thus leading to an excellent anode material for lithium-ion batteries with enhanced capacity and cycling property. Hierarchical SnO2/Fe2O3 heterostructures as lithium-ion battery anodes show a high initial discharge capacity of 1632 mA h g-1 at 400 mA g-1, and retained at 325 mA h g-1 after 50 cycles, significantly better than the anodes made of pure SnO2 nanosheets and a-Fe2O3 nanorods grown in similar conditions.In Chapter 4, We demonstrate the control doping of Sn into mesoporous TiO2 thin films by a facile, direct growth on conducting substrates (e.g. Ti foil) using the ligand-assisted evaporation-induced self-assembly method. The obtained Sn-doped mesoporous TiO2 thin films are polycrystalline with an anatase structure. The mesoporous TiO2 frameworks provide efficient ion transport pathways and structural stability for Li+ insertion. The in-situ incorporation of Sn dopants into the mesoporous frameworks improves the charge transfer efficiency and the theoretical Li+ storage capacity of the electrode. In addition, the obtained mesoporous structures on Ti substrates provide close contact between the active material and the current collector, thus reducing the contact resistance and enhancing the charge transfer. As proof-of-concept, lithium-ion battery measurement of the Sn-doped mesoporous TiO2 thin film anodes with different Sn doping ratios shows that the specific reversible capacity increases to a maximum with～6% Sn doping ratio (～252.5 mA h g-1 at 0.5 C) compared to our best pristine mesoporous TiO2 thin film anodes (100.8 mA h g-1 at 0.5 C), and then decreases at higher Sn doping ratios.In Chapter 5, based on the research of the Chapter 4, we further fabricate other transitional metal oxides doped titania mesoprous films. Using a facile, direct ligand-assisted EISA method, we obtained mesoporous thin films on Ti substrates. The addition of Fe dopants into the mesoporous frameworks provides higher theoretical Li+ storage capacity. Our research suggests that selective doping of other transition metal oxides into the mesoporous TiO2 thin films may provide a potential approach for obtaining LIB anode materials with enhanced capacity and stability.In Chapter 6, we provide a new device-designing concept. First, using the TBOT as the Ti sources to fabricate the titania nanowire film on the FTO substrate by the facile hydrothermal method. The 1-D titania nanowire has excellent photoelectric performance. Second, based on the TiO2 nanowire, we get the titania-meso-carbon composites. A mesoporous carbon layer is coated on the TiO2 nanowire via organic-organic self assembly of resol precursors and F127 template followed by carbonization at high temperature. Due to the photoelectric property of TiO2 and the electric double layer capacity of mesoporous carbon, we design a new concept solar-self-charge capacitor and the capacitance of this device needs further development.In Chapter 7, the whole thesis is summarized. |
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