Nano Assembled Graphene Layer - Nickel-manganese-cobalt And Its Nanocomposite Capacitance Properties

Electrochemical capacitor has attracted considerable attention over the past decades because of their high power density and long cycle life, and they can be used as the assistant and buffering systems for several primary power sources (e.g., electric vehicles, hybrid electric vehicles, and many typical stop-and-go systems) and the renewable energy generation systems. Although manganese cobalt nickel oxide (MnCoNiO2) is one of the most promising pseudocapacitor electrode materials due to its high specific capacitance, environmental compatibility and cost effectiveness, small specific surface area and low electrical conductivity restrict its application. Functionalized graphene (FRGO), a two-dimensional carbon nanosheet material with unique mechanic and electronic properties, offers a good opportunity to improve the electrical conductivity of manganese-based composite electrodes.This thesis mainly consists of three sections:Review, experiments and conclusion. Review part (chapter1) shows the preparation of MnCoNiO2nanosheets and FRGO nanosheets, their structure, property and application. In addition, the nanocomposites and their prepared methods as well as the preparation of carbon-based and transition metal oxide-based material electrodes by using for supercapacitor are also reviewered in this part. Experiment part (chapter2and chapter3) shows the assembly behavior between MnCoNiO2nanosheets and FRGO nanosheets by layer-by-layer self-assembly and spontaneous flocculation technique, and the electrochemical property of the FRGO-MnCoNiO2material electrode obtained by flocculation technique and (PDDA/MnCoNiO2/PDDA/RGO)10multilayer film obtained by layer-by-layer self-assembly method are investigated. A conclusion for the research is given in Chapter4. The main research works are as follows:1. Both MnCoNiO2nanosheets and FRGO nanosheets are firstly prepared from their precursors. Then FRGO-MnCoNiO2layered nanomaterial and (PDDA/MnCoNiO2/PDDA/RGO)8multilayer film is prepared by both a flocculated technology and a layer-by-layer assembling technology. The nanosheet assembling behavior is investigated by XRD, TEM, SEM, AFM, elemental analyses.2. Preparation of (PDDA/MnCoNiO2/PDDA/RGO)8multilayer films. Multilayer film is constructed on a quartz slide by a sequential adsorption of the positively-charged PDDA, the negatively-charged MnCoNiO2nanosheets, and the negatively-charged RGO nanosheets. In a typical process, the substrate is dipped in PDDA aqueous solution (2.5g dm-3) for20min to form a positively-charged surface and then rinsed thoroughly with ultrapure water and dried in flowing nitrogen gas. The PDDA-precoated substrate is then immersed in a colloidal suspension of MnCoNiO2nanosheets (0.4g dm-3) for20min, rinsed with ultrapure water, and dried in flowing nitrogen gas. The substrate is then dipped into the PDDA aqueous solution (20g dm-3) again to deposit another layer of PDDA. After rinsing with water and drying in flowing nitrogen gas, the substrate is dipped in the RGO nanosheet suspension (0.4g dm-3) for20min, then rinsed with ultrapure water and dried in flowing nitrogen gas to obtain the first MnCoNiO2/RGO nanosheet bilayer. A series of these operations is repeated n times to obtain the multilayer films (PDDA/MnCoNiO2/PDDA/RGO)n.3. Electrochemical property of FRGO-MnCoNiO2nanomaterial electrode and (PDDA/MnCoNiO2/PDDA/RGO)10multilayer film electrode. The FRGO-MnCoNiO2material cathode and (PDDA/MnCoNiO2/PDDA/RGO)10multilayer film cathode take full the pseudocapacitance advantage of the manganese-cobalt-nickel oxide, as well as the high electrical conductivity and stability of graphene. A strong synergistic effect between the MnCoNiO2and FRGO nanosheets is found in the FRGO-MnCoNiO2layered material and (PDDA/MnCoNiO2/PDDA/RGO)10multilayer film. This approach of exploiting synergies can be used to prepare the functional materials with desired properties for various applications.