Graphene/zno Nano Structure Materials In The Flexible Application Of Electrochemical Capacitors

Since the discovery of graphene in2004, it has been received wideresearch attention due to its good electronic conductivity, highlyoptical transparency, and extraordinary mechanical elasticity. Thepreparation and application of graphene and its composites inelectrochemical capacitors are currently research hot spots.In graphene-based electrochemical capacitors, mainly those usingreduced graphene oxide (rGO) devices, reduced graphene oxidesheets easily agglomerate in the electrode fabrication process. Eventhough this problem can be solved partially through constructing metaloxide/graphene or conducting polymer/graphene composites, theelectrodes will sacrifice the porous structure at the same time. Toaddress this problem, in this thesis, we first focus on the preparation of1D ZnO nanorods on CVD-graphene (chemical vapor depositiongraphene) and rGO films through hydrothermal method and themorphologies of1D ZnO. Then AZO (Al-doped Zinc Oxide) orCVD-graphene (chemical vapor deposition graphene) on flexible PET(polyethylene therephthalate) substrate is adopted as currentcollectors. On these current collectors, three-dimensional rGO/ZnO/rGOnanoscale composites that act as active materials of the electrodesare prepared under the temperature range of80-100℃usinghydrothermal method. ZnO nanorods with well control of densityprovide porous skeletons which enable the penetration of small rGOsheets into the space between nanorods. Large rGO sheets aresupported by vertically aligned ZnO nanorods to from thin rGO films. Thisstrategy enables the fabrication of porous structure as well as thecombine use of double-layer capacitance and pseudocapacitance.The main points and conclusions of this thesis are summarized as follows:1. Fabrication of one-dimensional vertically aligned ZnO nanorods on AZO, rGO and CVD graphene：（1）Preparation of AZO films with DC sputting. These AZO films serveas seed layers in the hydrothermal growth of ZnO or current collector inthe flexible electrode. Reduce graphene oxide with hydrazine and rGOsheets of the thickness of1nm are obtained.（2）Study of the impact of different substrates and reaction time onthe morphologies of ZnO nanorods. CVD graphene films are smoothand ZnO nanorods grown on them are highly oriented with high densitywhile ZnO nanorods on rGO films show bush-like morphologies due tothe rough nature of rGO films.2. Fabrication and characterization of the as-prepared flexiblegraphene/ZnO nanocomposites electrochemical capacitorelectrodes：（1） Fabrication of graphene/ZnO three-dimensional structureelectrodes and the morphologies study; By controlling the density ofZnO nanorods, large rGO sheets are supported to form films and smallsheets penetrate into space among ZnO nanorods.（2）Cyclic voltammetry (CV), charge-discharge behaviors andImpedance spectroscopy measurements of the graphene/ZnOthree-dimensional structure electrodes. The specific capacitance of thePET/CVD graphene/rGO/ZnO/rGO flexible electrode is68F/g underthe scanning rate of20mv/s. Its ERS is found to be50.