Study On Carbon-based Composite Electrode Materials For Supercapcaitor

Supercapacitors are newly power devices that occupy a region between batteries and dielectric capacitors on the Ragone plot describing the relation between energy and power. They have been touted as a solution to the mismatch between the fast growth in power required by devices and the inability of batteries to efficiently discharge at high rates. The electrode materials are supposed to be the most important factor that influences the performances of supercapacitors. Recently, considerable attention has been paid to develop three types of electrode materials for supercapacitors, including carbon materials, conducting polymers and metal oxides. Carbon materials are the most promising electrode materials for supercapacitors due to their large specific area, high electrical conductivity and high stability. However, low specific capacitance restricts their applications in high-power storage devices. The specific capacitance of conducting polymers or transition metal oxides are higher, nevertheless, the stability is relatively lower. Therefore, one promising approach is the fabrication of hybrid nanostructured electrodes by integrating polymers or transition metal oxides with a carbon host, where the carbon host serves as the conductive network.In this work, carbon-based composite electrode materials were prepared and used as electorde materials of supercapacitor. The main contents of this work are as follows:(1) Oxygen-rich activated carbon with three-dimensional network structure was prepared by chemical activation of coal tar residues with potassium hydroxide and subsequent carbonization treatment. Nanostructured FesO4/AC composite was then prepared by a simple chemical coprecipitation method and were used as a active electrode material for supercapacitor. The electrochemical behaviors of Fe3O4/AC nanocomposite were characterized in1.0mol dm-3Na2SO3electrolyte. It was shown that the specific capacitance of Fe3O4/AC nanocomposite was up to150F g-1at current density of3.0A g-1and was highly improved compared with that of Fe3O4or AC. Furthermore, as-prepared Fe3O4/AC nanocomposite exhibited excellent long cycle life without obvious capacitance fading even after1000charge/discharge cycles.(2) FeMoO4doped graphene composite was prepared by a facile hydrothermal method. The morphological and structural characterizations of FeMoO4/graphene composite were investigated by field emission scanning electron microscopy and X-ray diffraction measurements. The electrochemical behaviors were investigated using cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy in1.0mol dm-3Na2SO3electrolyte. It was shown that the specific capacitance of FeMoO4/graphene composites could reached to135F g-1at current density of1.0A g-1and was highly improved compared with that of graphene (66F g-1) or FeMoO4(96F g-1). Moreover, in comparison with pure-FeMoO4, FeMoO4/graphene composite exhibited lower electrochemical resistance and better cycle life.(3) Commercial CNT was refluxed in concentrated HNO3and H2SO4to achieve oxidised CNT. NiCoFe2O4/CNT composite was prepared by a facile hydrothermal method. The electrochemical behaviors of prepared composite were evaluated in6.0mol dm-3KOH electrolyte. It was shown that the specific capacitance of NiCoFe2O4/CNT composite could reached to145F g-1at current density of0.5A g-1and was highly improved compared with that of individual CNT (35F g-1) or NiCoFe2O4(121F g-1). Moreover, the specific capacitance of NiCoFe2O4/CNT composite retained around85.8%after500cycles.