Based On Super Capacitor Graphene Hydrogels And Its Preparation And Properties Of Composite Materials

Supercapacitors have been recognized as a unique kind of energy storage devices which exhibit high power density, long cycle life, and fast charging/discharging rate, having attracted enormous attention all over the world due to the increasing demand of power systems instantaneously delivering considerable energy. In recent years, most research in this area has been focused on the development of different electrode materials such as various forms of carbon, and transition metal oxides.Graphene, with its outstanding properties including a high theoretical surface area of over2600m2/g, good electrical conductivity, thermal stability, chemical tolerance and a broad electrochemical window, can be considered as an ideal candidate for electric double-layer capacitor (EDLC) electrode materials.In this dissertation, a three-dimentional (3D) self-assembled graphene hydrogel (GH) was prepared via a one-step chemical reduction at60℃using graphene oxide(GO) dispersion as the starting materials. Different reduction degree of GH were obtained by controlling the amount of the hydrazine hydrate. The effects of the specific surface area, disorder, wrinkling degree and oxygen-containing functional groups on electrochemical properties have been systematically investigated. The results demonstrate that the content of oxygen-containing functional groups on the GH sheets was the crucial factor. In two-electrode system, the highest specific capacitance of195F/g through galvanostatic charge/discharge measurements at a current density of lA/g was obtained using lmol/L H2SO4aqueous solution as electrolyte with addition of53ul hydrate hydrazine.Based on the above results,3D GH using different dispersion agents, such as water and ethanol were synthesized. Different reduction degree of graphene were obtained by controlling the amount of the hydrazine hydrate. The electrochemical properties demonstrate that the similar results was obtained for different dispersion agents. Meanwhile, compared with the samples obtained in the dispersion agent of ethanol, the better electrochemical properties can be presented using water as dispersion agent.In addition, the graphene-MnO2composite hydrogel (GH-MnO2) was prepared via a facile and cost-effective redox process. The reaction in situ between carbon atoms of graphene and KMnO4can lead to the deposition of MnO2nanoparticles throughout the porous3D GH network in order to obtain graphene-MnO2composite hydrogel with high specific surface area and mass-loading of the MnO2nanoparticles. When the concentration of KMnO4was0.1mol/L and reaction time was4h at room temperature, the as-prepared composite hydrogel exhibit high specific capacitance, excellent rate capability, and exceptional cycling stability. With the graphene-MnO2composite hydrogel as electrodes, the specific capacitances of254F/g can be obtained at a current density of0.2A/g using6 mol/L KOH aqueous solution as electrolyte. Furthermore, the80.3%capacitance was retained after1000cycles. The composite expect to have potential applications as electrodes for supercapacitors.