Transition Metal Oxide / Preparation And Capacitance Properties Of Nano-electrode Material Graphite Ene

Electrochemical capacitors have attracted considerable attention over the past decades because of their great advantages such as high power supply, long cycle life, and low cost. The capacitive property of the electrochemical capacitors is influenced by the electrode materials, electrolyte, and the assembled device, with the most important factor being the electrode materials. Because graphene has high electrical conductivity, good electrochemical stability, high surface area and superior mechanical property, it is considered to be the most potential electrical double-layer capacitor material. However, the actual capacitive behavior of pure graphene is much lower than its theory value due to the serious agglomeration during preparation. It has been found that the capacitance of graphene can be improved by combining with some pseudocapacitive electrode materials, such as transition-metal oxides. Among the transition-metal oxides, layered manganese oxide, layered ruthenium oxide, and vanadium oxide have received tremendous attention for electrochemical capacitors. Therefore, the capacitive performance of electrochemical capacitor is expected to be improved by a nano-scale hybriding between graphene and metal oxide nanosheets. In the present thesis, a series of metal oxide/graphene with excellent capacitive property have been prepared by a nanosheet assembling technology between graphene and metal oxide nanosheets, and their capacitance are systematically investigated. The main content of the research is as follows:The manganese oxide/graphene (MnO2/GR) layered nano-scale electrode material has been prepared by a nanosheet assembling technology between graphene nanosheets and manganese oxide nanosheets at room temperature, and the capacitance of the prepared hybrid materials is investigated. The experimental results indicate that the MnO2/GR layered nano-scale electrode material with MnO2content of18%shows the highest specific capacitance. An asymmetric electrochemical capacitor with high energy and power densities is assembled based on MnO2(18%)/GR electrode material as positive electrode and GR as negative electrode in a neutral aqueous Na2SO4solution as electrolyte. The asymmetrical electrochemical capacitor could cycle reversibly in a voltage of0-1.7V and gives an energy density of10.03Wh kg-1even at an average power density of2.53kW kg-1. Moreover, the asymmetrical electrochemical capacitor also exhibits excellent cycle stability, and its capacitance retention is69%after repeating the galvanostatic charge-discharge10000cycles at a constant current density of2.23A g-1.Graphene/multiwall carbon nanotubes/MnO2(GR/MCNT/MnO2) nano-scale electrode material with a specific capacitance of126F g-1within a potential window of0to1.1V vs. saturated calomel electrode has been synthesized by a simple redox reaction between graphene/multiwall carbon nanotubes (GR/MCNT) and KMnO4at room temperature. The research results indicate that the GR/MCNT/MnO2electrode material with MnO2content of37%shows the highest specific capacitance, in which MnO2posses a layered structure. An asymmetric electrochemical capacitor is assembled by using GR/MCNT/MnO2electrode material as positive electrode and GR/MCNT material as negative electrode, respectively in1mol L-1Na2SO4aqueous electrolyte. The asymmetric EC can cycle reversibly in a potential window of0-2.0V and gives a high energy density of28.33Wh kg-1, which is much higher than those of symmetric electrochemical capacitors based on GR/MCNT/MnO2//GR/MCNT/MnO2(6.20Wh kg-1) and GR/MCNT//GR/MCNT (3.92Wh kg-1). Moreover, the asymmetric electrochemical capacitor presents a high power density (5kW kg-1at13.33Wh kg-1) and excellent cycling performance of83%retention after2500cycles.Ruthenium oxide with layered structure has been synthesised by heating a mixture of Na2CO3:Ru:RuO2·xH2O=2:1:3under an argon flow at900℃for12h. The layered ruthenium oxide is delaminated into ruthenium oxide nanosheets in a tetramethylammonium solution at TMA+/H+(molar ratio of tetramethylammonium ions over exchangeable protons in H-RuO2)=1, and RuO2nanosheets with a thickness of about1.3nm are obtained. Ruthenium oxide/graphene (RuO2/GR) nano-scale layered electrode materials for high performance electrochemical capacitor are prepared by a solution-phase assembly technology between RuO2nanosheets and GR nanosheets at room temperature. RuO2/GR electrode materials with different RuO2amounts keep a layered structure and show randomly dispersed, thin, crumpled sheets morphology. The high dispersion and strong interaction between the RuO2and GR nanosheets maintains a high structural stability for the layered electrode material, and causes an obvious synergistic effect between the RuO2and GR nanosheets. A specific capacitance of998F g-1is obtained for RuGR46electrode material electrode based on the RuO2content of40%. The utilization of RuO2in the RuGR46electrode material increases by adding GR, and the capacitance of RuGR46is quite comparable to that of the pristine RuO2·xH2O while60wt%of RuO2could be saved. The charge transfer resistance of RuGR46electrode is larger than that of GR electrode while smaller than that of the pristine RuO2·xH2O electrode. A symmetric electrochemical capacitor based on the RuO2/GR electrode is assembled in0.5mol L-1H2SO4solution as the electrolyte in a voltage of0-1.2V, and it could cycle reversibly and gives a high energy density of20.28Wh kg-1, also exhibits a high energy density of14.03Wh kg-1even at a power density of12kW kg-1and presents an capacity retention of94%at a constant current density of5A g-1for1000cycles.Graphene/VO2(GR/VO2) nano-scale electrode material has been prepared by hydrothermal treatment the suspension of ammonium metavanadate and graphite oxide. The research results indicate that VO2particles are embedded uniformly on the surface of graphene and the content of graphen is8.3%in the GR/VO2electrode material. A specific capacitance of225F g-1is obtained within a potential window of-0.2to0.8V vs. saturated calomel electrode for GR (1.0)/VO2electrode, which is higher than that of pure GR and VO2electrodes. Moreover, the cycle stability for GR (1.0)/VO2electrode becomes excellent due to the adding of GR in compare with pure VO2. An asymmetrical electrochemical capacitor is assembled by using GR (1.0)/VO2electrode material as positive electrode and GR material as negative one. The asymmetrical electrochemic capacitor can cycle reversibly in a cell potential of0-1.7V and gives a high energy density of22.8Wh kg-1, which is much higher than those of symmetric electrochemical capacitors based on GR(1.0)/VO2(8.33Wh kg-1) and GR (4.03Wh kg-1).