Graphene - Silver Preparation And Capacitance Properties Of Composite Materials Research

Graphene has been widely used in many fields, such as sensor, drug carrier, catalysts, lithium ion secondary battery and supercapacitor because of its special physical and chemical properties. In this thesis, graphene-silver nanocomposite has been prepared by a simple in-situ simultaneous reduction process of both Ag+ions and graphite oxide, and the influence of the Ag+concentration, the reduced condition, and the reductant type on the structure and morphology of the obtained materials has been researched. Moreover, the electrochemistry property of the obtained graphene-silver nanocomposite has also been investigated.This thesis mainly consists of three sections, introduction, experimental and conclusion. Introduction part (chapter1) reviews the structure, classification, preparation method and the application of graphite oxide, graphene, and graphene-based nanocomposite. Experimental part (chapter2) describes the preparation and characteristic of graphene-based nanocomposite by a simple in-situ simultaneous reduction process of both Ag+ions and graphite oxide, and the influence of the Ag+concentration, the reduced condition, and the reductant type on the structure and morphology of the obtained materials has been discussed. In chapter4, the electrochemical property has been investigated by cyclic voltammetry and electrochemical impedance spectroscopy in2.0mol L-1KNO3electrolyte. The research conclution is finally presented in chapter4.By using improved Hummers method, graphite oxide (GO) with a basal spacing of0.73nm is firstly prepared. Then the graphite oxide suspension (100mL0.5mg mL-1) and a AgNO3solution (100mL0.02mol L-1) is mixed, and the obtained suspension is treated by ultrasonic treatment (600W,80%amplitude) for1h and followed by stirring at room temperature for12h. The suspension is separated by centrifugation, and the obtained sediment is washed with deionized water for several times, Ag+ion intercalated GO is obtained, which is abbreviated as GO-Ag+. GO-Ag+nanocomposite (200mg) is soaked in200ml deionized water, and hydrazine hydrate (200μL) is then added into the suspension. The obtained suspension is stirred for30min and heated at95℃for12h, the black sediment is washed with deionized water and dried in air, and graphene-Ag nanocomposite is finally obtained by a simple in-situ simultaneous reduction process of both Ag+ions and graphite oxide, which is abbreviated as RGO-Ag. The optimal preparation conditions of RGO-Ag nanocomposite are as follows:the ion exchange ratio of Ag+ions is10, hydrazine hydrate is used as reductant, and the reduced temperature is95℃for12h. The structure and morphology of the obtained material are examined by XRD, SEM, TEM, FT-IR, and XPS.Electrochemical property is characterized by cyclic voltammetry and electrochemical impedance spectroscopy in2.0mol L-1KNO3electrolyte. RGO-Ag nanocomposite electrode shows a characteristic faradic capacitance behavior, and the specific capacitance value is220F g-1at a scan rate of10mV s-1, which is much higher than that of the graphene electrode (140F g-1). The high capacitance is ascribed to the large pseudocapacitance from the residual C-O and C=O function groups, high electrical conductivity, and less aggregation of the graphene nanosheets due to the existence of Ag particles.