Synthesis Of Graphene Based Nanocomposite Materials And The Application In Electrochemistry

As an ideal two-dimensional nanosheet with unique structure and excellent properties,graphene has been the research focus in recent years. The two-dimensional plane structure of graphene is suitable for loading different kinds of nanomaterials, and its excellent conductivity can improve the electrical conductivity of the nanocomposites. Multicomponent composite materials can exhibit the advantages of various components and realize the synergistic effects between different materials. Various methods have been used to synthesize graphene-based composites. Among them, electrochemical method has shown the advantages including low cost, easy operation and high production purity. Graphene can be directly formed on the surface of electrodes or nickel foam by electrochemical technique.In this thesis, electrochemical method was used to synthesize graphene film on the surface of carbon ionic liquid electrode(CILE) or nickel foam(NF). Then nanocomposite such as Zr O2/graphene, Zn O/graphene, Mn O2/graphene, Co(OH)2/graphene and Ni O/graphene were further prepared through electrochemical approach, which had excellent electrochemical performance and the application of these graphene based nanocomposite in electrochemical sensors or supercapacitors were further investigated. The main results of the research are summarized as follows:1. Multilayers of graphene(GR) and myoglobin(Mb) modified electrode was fabricated with a layer of chitosan film. Electrochemical behaviors of the modified electrode were studied by cyclic voltammetry, which exhibited a couple of well-behaved stable and nearly reversible redox peaks, indicating that Mb realized its direct electron transfer on the biosensor. The experimental result may be accredited to the existence of multilayers conductive GR nanosheets that could provide big specific surface area, fine biological compatibility and ultrahigh electron transfer route for the immobilized Mb. The catalytic reduction peak currents of this biosensor to the detection of trichloroacetic acid were established from 0.6 to 26.0 mmol/L accompanied with the detection limit as 0.15 mmol/L(3?). Therefore a novel third-generation mediator-free electrochemical sensor was successful prepared with the usage of multilayers of GR.2. An electrodeposited zirconia(Zr O2) nanoparticle and graphene(GR) nanosheets modified carbon ionic liquid electrode(CILE) was fabricated to get a modified electrode that denoted as Zr O2/GR/CILE, which was further used for the immobilization of myoglobin(Mb). The performances of Zr O2/GR/CILE were checked by scanning electron microscopy and electrochemical methods, and the result indicated the formation of nanocomposite on the electrode surface with increased surface area. Direct electrochemistry of Mb was realized on the modified electrode with a pair of well-defined quasi-reversible redox peaks appeared, which was ascribed to the typical electrochemical behaviors of Mb Fe(III)/Fe(II) redox couples. Therefore the presence of Zr O2/GR on the electrode could provide a specific interface for accelerating the electron transfer of Mb with the underlying electrode. Electrochemical behaviors of Mb were carefully investigated with the electrochemical parameters calculated. Under the selected conditions the Mb modified electrode exhibited excellent electrocatalytic activity to the reduction of trichloroacetic acid in the concentration range from 0.4 to 29.0 mmol/L with a detection limit of 0.13 mmol/L(3?).3. Zn O/graphene nanocomposite was prepared by electrodeposition on the surface of CILE step-by-step. Scanning electron microscopy(SEM) was used to check the surface morphorography of the nanocomposite. As an electrode material in supercapacitor, cyclic voltammetry, chronopotentiometry and A.C. impendance were used to check the eletrochemical performances. The results indicated that the presence of graphene improved the whole capacitance. The electrode material had a specific capacity of 46.31 m F/cm2 at the current density of 3 m A/cm2, and had a good cycling stability.4. Mn O2/graphene nanocomposite was synthesized by the electrochemical method.Scanning electron microscopic(SEM) images shown that Mn O2 nanoparticles were uniformly loaded on the surface of three-dimensional graphene. By using Mn O2/graphene as the electrode material in supercapacitors, different methods such as cyclic voltammetry,chronopotentiometry and A.C. impendance were used to check the capacitance properties.The results indicated that the Mn O2/graphene composite could improve the capacitance.The electrode material had a specific capacity of 36.42 m F/cm2 at the current density of 3m A/cm2, and had a good cycling stability.5. The Co(OH)2/graphene nanocomposite was successfully synthesized on the surface of CILE through a facile two-step electrodeposition approach and then directly applied as the electrode for a high-performance supercapacitor. The structure and morphology of the prepared Co(OH)2/graphene nanocomposite was characterized by field-emission scanning electron microscopy(SEM). The subsequent electrochemical measurements show that Co(OH)2/graphene nanocomposite possesses a superior specific capacitance of 730.23 m F/cm2 at a current density of 5 m A/cm2. And 80% of the specific capacitance is retained after 3000 cycles at a current density of 20 m A/cm2. Owing to its favorable electrochemical performance, the Co(OH)2/graphene nanocomposite has great potential in future commercial electrochemical supercapacitors.6. In this section, simple two-step electrodeposition was used to synthesize Ni O/GR nanoflake on the surface of nickel foam(NF). The results of scanning electron microscopy have shown that Ni O nanoflakes were uniformly loaded on the GR/NF. The cyclic voltammograms showed that the electrochemical performance of Ni O/GR nanocomposite had an obvious improvement compared with single materials, resulting from synergistic effects of two kinds of material. The subsequent electrochemical measurements showed that the Ni O/GR/NF electrode possessed a specific capacitance of 381 m F/cm2 at a current density of 1 m A/cm2, which was potential in the supercapacitor application.