| Nowadays,problems in energy and environment areas are becoming more and more challenging,which leads our whole society to great demand of more efficient energy-consuming and new energy developing.Electricity,which is a kind of convenient,low-cost and clean power source,has become indispensable in the modern world.The power density of batteries is commonly lower than supercapacitors’,which allow much more charge-discharge cycles than the former.Supercapacitors can manager to work in large temperature windows.Although supercapacitors are attracting more and more researchers’ attention,they are still faced with a bottle-neck,that is low energy density.In the near 20 years,nano-technologies have been increasingly booming,which inject new blood into supercapacitor’s research.The purpose of this thesis is to develop better transition metal compound（TMC）/graphene composite materials for supercapacitors,which possess better electrochemical performance including specific capacitance,cyclic-stability,etc.As Ni or Co-based pseudocapacitors,which are more inexpensive than Ru-based ones and have bigger specific capacitance than Mn-based ones,are regarded as new a generation of pseudocapacitors.But otherwise,Ni or Co hydroxide is limited by poor cyclic-stabilities.Thus we chose NiCo2O4 as the expected materials.Supercapacitors have stepped into a rapid developing route since the discovery of graphene by two Russian-British researchers.Graphene is formed by honey-comb shape 2-dimentional lattice of pure carbon atoms,which allows it presents a promising application for supercapacitor devices.It has a large specific surface,onto which other active substrate can be combined,providing higher capacitance and energy densities.Firstly,we synthesized high-qualified single-layer graphene-oxide（GO）nano-mateiral as the precondition for the following devices development.Secondly,we combined NiCo2O4 active materials and graphene materials through an electrodeposit method,which enhances the pseudocapacitor performance of NiCo2O4 electrode including specific capacitance,cyclic-stability,etc.The following is the main content of this thesis:（1）A modified Hummers method was adopted to synthesize graphite oxide,followed by a sonication method to exfoliate it into single-layer graphene oxides,which was the fundamental of subsequent electrode developing.Single-layer GO（graphene oxide）was characterized by AFM.We discussed the difference between modified Hummers method and original Hummers method and explained how the former modified GO’s property.After GO was chemically or electrochemically reduced,single-layer graphene was made,which possesses large specific surface area,good electrical conductivity and electrochemical stability according to the literature.Single-layer graphene can avoid some unpredictable problems caused by multiple-layer one,that make it easier to combine with pseudocapacitor materials.（2）Electrodeposit method was adopted to develop NiCo2O4 pseudocapacitor electrodes,followed by characterizations.Ni,Co compounds,of which the raw materials are inexpensive,possesses relatively higher specific capacitance and stronger chemical-stability,becoming a kind of promising pseudocapacitors.（3）We made NiCo2O4/RGO hybrid electrodes by electrodeposit method,followed by electrochemical characterizations,of which the results were compared with（2）.We found out what the role of RGO is in the electrodes and the determine factors.NiCo2O4/RGO electrodes exhibited larger specific capacitance than NiCo2O4 electrodes,contributing to the good electrical conductivity of graphene that activated the second oxidation peak of NiCo2O4.Meanwhile,because of its electrochemical stability and physical stability,graphene had enhanced electrode’s cyclic stability. |
