The Preparation Of Silver/manganese Oxide Nanocomposites And Their Capacitance Performance Study

Because the synergy effect between each component of the nanocomposites may compensate the drawback of single functional material, nanocomposites have been widely investigated and applicated by researchers in the field of optical, electrical, magnetic, and biological sensors. Manganese oxides with different structure and morphology have not only abundant resource, low cost, environment compatibility, but also high theoretical capacitance, and they are important functional materials. Although manganese oxides show high theoretical capacitance, the semiconductor character restricts their application in supercapacitor as electrode material. Therefore, by using the synergy effect of each component of nanocomposites, the metal nanoparticles with good conductive property will be intercalated into the interlayer of the layered manganese oxide, and the nanocomposites with high capacitance and good conductive property are expected to be prepared.This paper mainly consists of three sections, review, experiments and electrochemical peoperties of the prepared materials. The structure, property, preparation method, exfoliation technology of the layered manganese oxide and its application are firstly reviewed, and the overview of nanocomposites and their synthetic methods, as well as the preparation of MnO2-based nanocompounds by using for supercapacitor as electrode materials are also reviewed in Chapter1. In the experiment section (Chapter2, and Chapter3), Ag/MnO2nanocomposites are prepared by an ion exchange method and an exfoliation/reassembling technology, respectively, in which layered manganese oxide is acted as precursor. The research on the electrochemical property of the Ag/MnO2nanocomposite obtained by an exfoliation/reassembling technology is carried out in Chapter4.The main research works are as follows:(1) The preparation of Ag/MnO2nanocomposites by an ion-exchange method. By using H-type layered manganese oxide (H-BirMO) as precursor, it is exchanged with AgNO3solution with different volumes for48h, Ag+intercalated layered manganese oxide is obtained. Ag+intercalated layered manganese oxide is then soaked in a solution of ethanol containing poly(N-vinylpyrrolidone)(PVP), the Ag+ions existed in the interlayer are reduced into Ag nanoparticles, and Ag/MnO2nanocomposite is finial obtained. The reserch results show that the amount of Ag+ions intercalated into the interlayer of manganese oxide is little because of the inetrcalation resistance of the layered structure, and Ag/MnO2nanocomposite with good dispersation and uniform size of Ag nanoparticles is not obtained by the ion-exchange method. The obtained materials at different stages are characterized by XRD, TEM and AAS.(2) The preparation of Ag/MnO2nanocomposite with good dispersation and uniform size of Ag nanoparticles by an exfoliation/reassembling technology. H-type layered manganese oxide is firstly delaminated into manganese oxide nanosheets in a tetramethleamine hydroxide (TMAOH), the delaminated manganese oxide suspension is then mixed with a AgNO3solution with different volumes for24h, the intermediate product, Ag2O intercalated manganese oxide is obtained. Ag2O/MnO2intercalated manganese oxide is soaked in a solution of ethanol containing poly(N-vinylpyrrolidone), the Ag2O existed on the surface of manganese oxide are reduced into Ag nanoparticles, and Ag/MnO2nanocomposite with good dispersation and uniform size of Ag nanoparticles is finial obtained by an exfoliation/reassembling technology. The effect of AgNO3solution and PVP on the structure and morphology of the obtained materials is investigated. The research results show that the reassembling process of the manganese oxide nanosheets is effectively prevented and manganese oxide nanosheets exist in a complete exfoliation state in Ag/MnO2nanocomposite. Ag nanoparticles with a size of about5nm are highly monodispersed on the manganese oxide nanosheets without agglomeration. The obtained materials at different stages are characterized by XRD, TEM, XPS and AAS.(3) Electrochemical property of Ag/MnO2nanocomposite. By using a three electrode system, the electrochemical property of Ag/MnO2nanocomposite is characterized by cyclic voltammetry and electrochemical impedance spectroscopy in1mol L-1Na2SO4electrolyte. Ag/MnO2nanocomposite electrode shows a characteristic Faradic capacitance behavior, and the specific capacitance value is272F g-1at a scan rate of10mV s-1,much higher than that of the manganese oxide nanosheet electrode (90F g-1). The introduction of Ag nanoparticles into manganese oxide nanosheet electrode can significantly improve the electrical performance due to the increase in conductivity.