Catalytic Synthesis And Supercapacitor Performance Of Graphene-based Materials Using Nanoporous Nickel

With the fast-growing demand of miniaturized and portable devices,tremendous efforts have been devoted to the research of the supercapacitor with remarkablely high volumetric energy density.Three dimensional(3D)graphene with excellent conductivity and stability,and nickel cobalt layered double hydroxides(NiCo-LDHs),with abundant oxidation states and high theoretical capacity,exhibit great potential to advanced supercapacitor storage systems.However,the applications of 3D graphene and NiCo-LDH in the micro-power system are usually limited by some drawbacks,such as sizable pores,poor conductivity and inferior utilization of electrodes.Therefore,it is urgent to explore a novel method to fabricate the free-standing electrodes with high mass loading and superior utilization.In this thesis,the free-standing 3D nanoporous graphene and its hybrids films are successfully fabricated by chemical vapor deposition(CVD)approach using nanoporous nickel as the substrate and catalyst.The effects of CVD parameters,doping treatment and deposition time on the morphology and structure of as-fabricated samples are studied systematically.In addition,the factors influencing the performance of 3D nanoporous graphene and heterogeneous NiCo-LDH are discussed,as well as the electrochemical performances and interaction mechanism.Using as the supercapacitor electrodes,the heteroatom doping and pore size of3D graphene films are systematically studied in the electrochemical experiment.Compared with macroporous graphene films,nanoporous graphene films exhibit an extraordinarily high packing density and large operational window in neutral,acidic and alkaline aqueous electrolytes.Nitrogen and oxygen doping play different roles in different aqueous electrolytes on the electrical conductivity and pseudocapacitance of3DNG.The high packing density of 3.65 mg/cm~2,the maximum working window and the synergistic effect between N and O doping,give rise to a high areal capacitance of435 mF/cm~2 in neutral electrolyte and excellent cycle stability of 99.5%after 5000cycles.Nanotubular Ni supported N-doped graphene(ntN-NG)film with hydrophilic surface,high specific surface area and appropriated pore size is obtained using the combination of pre-calcination and CVD approachs,where the coarsing process of NPN at high temperature is controlled.In addition,hierarchical NiCo-LDH nanoneedles/nanosheets architecture are deposited onto the surface of ntN-NG film via hydrothermal approach.Furthermore,the active mateirals almost fully fill the naonotubular pores of ntN-NG,which enhance the mass loading and utilization of electrode dramatically.The hybrids exhibit a record high volumetric capacitance of 867 F/cm~3 at 1 mA/cm~2 and remarkable cycling stability of 89.4%retention after 10000 cycles.