Preparation And Characterization Of Composite Electrodes Capacitance Nanotubes / Manganese Oxide Nano

With wide usage of the new energy, the energy storage devices with high energy and power densities, low cost and long cycle life have drew wide attentions. Supercapacitor is one of the key technological systems that lead the state-of-the-art electrical energy storage systems, which can charge and discharge more quickly than battery, and have much higher capacitance than common capacitor. Over the past few decades, the hybrid nanocomposites show a synergy effect between each component and the material functional drawback can be compensated. Therefore, these hybrid nanocomposites have been widely applied in many fields such as optical, electrical, magnetic, and biological sensors. In particularly, the faradaic pseudocapacitor based on transition metal oxides has attracted significant attention owing to its high specific capacitance, excellent reversibility and long cycle life. Among these transition metal oxides, manganese oxide is good candidate supercapacitor electrode material because of its abundance, low-cost, good electrochemical reactivity and environmental friendliness in comparison with the ruthenium oxides or other transition metal oxides. Although bulk manganese oxides show good capacitance, the small specific surface area and low electrical conductivity seriously limited their applications as the electrode materials of supercapacitors. Therefore, manganese oxide hybrid electrode materials with good capacitance, large specific surface area and high electrical conductivity are expected.Manganese oxide nanosheets have not only distinctive physicochemical properties, associated with dimensions in the nanometer scope, but also a large specific surface area. They can be obtained through the delamination reaction of the layered MnO2and can be employed as a new class of nanoscale materials. Because of the excellent electronic conductivity of carbon nanotubes it would be an ideal conductor to form electron-transferring channels during manganese dioxide discharging. Therefore, the MnO2-carbon nanotube hybrid nanomaterials are expected to improve the capacitance and electrical conductivity of the obtained materials as supercapacitor electrodes. Sophisticated functionalities or nano-devices may be designed through the selection of manganese oxide nanosheets and carbon nanotube over their arrangement at the molecular scale. This paper mainly consists of three sections, review, experiments and research results. The structure, property, preparation method of the layered manganese oxide and carbon materials as well as the exfoliation technology are firstly reviewed, and the overview of nanocomposites and their synthetic methods, as well as the preparation and characterization of MnO2-based nanocompounds by using for supercapacitor as electrode materials are also reviewed in Chapter1.In the experiment section (Chapter2, Chapter3, and Chapter4), the research on the preparation and electrochemical property of manganese oxide nanosheets/functional carbon nanotube hybrid nanomaterial and the manganese oxide nanobelt/functional carbon nanotube hybrid nanomaterial is carried out.The main research works are as follows:(1) The preparation of both MnO2nanosheets and the functionalized carbon nanotube. Na-type layered manganese oxide is prepared as reported in the literature. The obtained Na-type layered manganese oxide is treated with HCl solution to produce H-type layered manganese oxide, which is abbreviated as H-BirMO. Delamination of the precursor H-BirMO is carried out by an ion-exchange method. The precursor H-BirMO is treated in the solution of TMAOH at room temperature. After soaking, the obtained colloidal suspension is centrifuged to remove any unexfoliated layered manganese oxide, the delaminated manganese oxide nanosheets was obtained. The functionalized CNTs (CNT-NR34) were obtained by follow three steps. At firstly, carbon nanotube is refluxed in a mixed solution of H2SO4/HNO3(3/1v/v) at70℃for3hour, carboxylic acid functionalized CNTs (CNT-COOH) are obtained. Secondly, CNT-COOH is reacted with SOC12and refluxed for12h at70℃, and then reacted with NH2(CH2)2N (CH3)2in dehydrated toluene for24hour at room temperature after evaporating remaining SOCl2, amine functionalized CNTs (CNT-NR2) is obtained. Thirdly, amine functionalized CNTs (CNT-NR2) is followed by reacting with CH3I in acetone for24hour at room temperature, the resulting precipitate is washed with deionized water and drying at vacuum for24hour, the functionalized CNTs are finally obtained, which is abbreviated as CNT-NR3+and dispersed in deionized water for using.(2) The preparation of CNTs-MnO2hybrid layered nanomaterials by a flocculation technology. The delaminated layered manganese oxide (MnO2) suspension (1mg mL-1) and the functionalized CNTs (CNTs-NR3+) dispersion (1mg mL-1) are mixed, treated by ultrasonic treatment, the resulting sediment is collected by centrifugation, followed by washing with distilled water and finally freeze-dried in vacuum for24h, CNTs-MnO2hybrid layered nanomaterial is obtained.(3) Preparation of manganese oxide nanobelt/CNTs hybrid nanomaterials. The precursor K-birnessite layered MnO2is prepared by a Sol-Gel method. Then the manganese oxide nanobelt and the functionalized CNTs are dispersed into NaOH solution (6mol L-1) and the obtained suspension is hydrothermally treated at150℃for30h, the manganese oxide nanobelt/CNTs hybrid nanomaterials are obtained.(4) Electrochemical property of both CNTs-MnO2hybrid layered nanomaterials and manganese oxide nanobelt/CNTs hybrid nanomaterials. The electrochemical performances of the as-obtained nanomaterial electrodes are tested using a cyclic voltammetry (CV) method and electrochemical impedance spectroscopy (EIS) with a three-electrode electrochemical setup in Na2SO4electrolyte. The working electrode is prepared by mixing the prepared hybrid nanomaterials (75wt.%) as active one with acetylene carbon black (20wt.%) and polyvinylidene fluoride (5wt.%). For the CNTs-MnO2hybrid layered nanomaterials, a strong synergistic effect between the functionalized CNTs and exfoliated manganese oxide nanosheets is observed. The doped CNTs not only increase the utilization of manganese oxide nanosheets in the active cathode material, but also enhance its performance at the high rate charge and discharge. The capacitance of CNTs-MnO2hybrid layered nanomaterial electrode still keeps about285F g"1by doping low capacitance CNTs from-0.2to0.8V at a scan rate of5mV s-1. A relative high specific capacitance of151Fg-1can be maintained even at a high scan rate of100mV s-1. For the manganese oxide nanobelt/CNTs hybrid nanomaterials, the specific capacitance is178F g-1from-0.2to0.8V at a scan rate of5mVs-1.The obtained materials at different stages are characterized by FT-IR, XRD, SEM and TEM.