Preparation Of Graphene And Graphene Based Binary And Ternary Nanocomposites And Their Application In Supercapacitors

Super capacitor with high power density, long cycle life, andenvironmental protection has been a research hotpot. Scientists and researchunits around the world at present are dedicated to the study on how toimprove the energy density and power density of super capacitor, shorten thecharging and discharging time? However, the key to solve these problems isto find a good super capacitor electrode material. Graphene has the goodelectrical conductivity, the large specific surface area and strong mechanicalstrength. Graphene in the field of super capacitor electrode materialsshowed great application prospect. At present, for the sake of large-scale,low-cost preparation of graphene, chemical reduction of graphene oxide isused. However in the process of reduction, a traditional hydrazine hydratereductant is toxic, environmental pollution, and the as-prepared graphene iseasy to renite, severely limiting the graphene and graphene compositeapplication. Therefore, this paper based on the analysis of graphene based on recent research and application of the results, carried out a water solublegraphene and graphene-conductive polymer binary composite,graphene-conductive polymers-transition metal oxides ternary composites.The structure and morphology of the composites were characterized by SEM,XPS, XRD, FT-IR and BET. Graphene and graphene-based compositematerial as a super capacitor electrode material of electrochemical capacitorare also studied, and achieved the following results:（1） The thermal alkali reduction process of graphene oxide was studiedby carbonate sodium, compared with traditional chemical reduction agenthydrazine and reported potassium hydroxide. The research found that specificsurface area of Na₂CO₃-Graphene and K-Graphene were789and632m²/g,respectively. However, specific surface area of H-Graphene was420m²/g.The conductivity of Na₂CO₃-Graphene and K-Graphene were10and12.8S/m. however, the conductivity of H-Graphene was187.5S/m.Electrochemical tests show that Na₂CO₃-Graphene has ideal specificcapacitance of228F/g at the current density of5mA/cm². Therefore, Na₂CO₃thermal solution is an effective and low cost green chemical reduction agentfor the reduction of graphene oxide. It can be used for mass productionreduction graphene oxide and a large number of the graphene electrodematerial for electrochemical capacitors.（2） With graphene oxide acid solution as the water phase,trichloromethane as the oil phase, respectively, the ammonium persulfate （APS） and aniline were added to the water phase and oil phase.Graphene-oxide/polyaniline composite was prepared via oil/water interfacialpolymerization. The results showed that hydroxyl （-OH） and carboxyl（-COOH） groups of graphene oxide and polyaniline had chemical bonds andhydrogen bonds. HRTEM and SEM show that the generated fibrous ofpolyaniline is evenly distributed on the surface of graphene oxide.Electrochemical results indicated that a high specific capacitance of893F/gfor the hybrids was measured at the potential scan rate of5mV/s in a6MKOH aqueous solution compared to244F/g for pure PANIF and26F g-1forGO.（3） Using sulfonated graphene acid solution as the water phase,trichloromethane as oil phase, the APS and aniline were added to the waterphase and oil phase, respectively. Different mass feed ratios ofSDBS-Graphene and aniline in the interfacial polymerization was alsoinvestigated to select the SDBS-Graphene-PANI-F （SGEPA） composites bytheir effect on the supercapacitor performance. It can be found that thecomposites show high specific capacitance and good cycling stability whenmass ratio of PANI-F to SDBS-Graphene is10. The SGEPA compositeelectrodes with a mass ratio of1:10showed better electrochemicalperformance than pure polyaniline nanofiber and graphene. A high specificcapacitance of962F/g was obtained at a potential scan rate of2mV/s and thespecific capacitance value of SGEPA-110retained about78%after1000 cycles. It also exhibited a high energy density of68.86Wh/kg at a powerdensity of102W/kg. The extraordinary electrochemical properties of thecomposites were attributed to the well-designed structural advantages ofbinary nanocomposites and the good combination and synergistic effectsbetween graphene and polyaniline.（4） Aniline is used to restore graphene oxide. The use of aniline on theoxidation process lost electrons. Electrons are captured by graphene oxide.Graphene-polyaniline oligomer is formed. Then directly adding concentratedhydrochloric acid in a solution and then dispatch the pH of the solution to1,to join the initiator APS, reaction in the ice water bath to get graphene-polyaniline composite material. This advantage is one step solution method isused to preparation of graphene-polyaniline composites, it avoidagglomeration of graphene in the solution, at the same time the graphenesurface adsorption of aniline oligomer, which also limits its further together,thereby ensuring the polyaniline state before single layer graphene dispersionpolymerization. And this reaction did not plus a reducing agent for reductionof graphene oxide, thus avoid the effect of reducing agent on the compositematerial. Different mass ratio of graphene oxide and aniline were studied.Electrochemical tests show that when aniline and graphene oxide mass ratiowas1:8（GPA8）, the specific capacitance values can reach2033F/g at1mv/s.It is noted that the specific capacitance of GPA8is959F/g at0.5A/g and stillkeeps as high as480F/g even at5A/g. However, the specific capacitance of PANI decreases from155to38F/g at current densities of0.5and5A/g,respectively. After100cycles, the redox peaks for GPA8electrode are stillpresent, indicating a good cycling performance with capacitance retention of80%.（5） Using GO+SnSO₄+H₂O-Graphene+SnO₂+H₂SO₄, we adopt one-potmethod to prepare graphene-SnO₂-polyaniline ternary composite; itselectrochemical performance was studied. Research found that as polyanilinein the proportion of ternary composite increased, capacitance value will beincreased dramatically. When the scan rate is5mV/s, the capacitance value ofGSP118ternary composite can reach913.4F/g. However, the capacitancevalue of GS11composite can only reach38.4F/g. Moreover, GSP ternaycomposite can become more stability due to the indroduction of SnO₂.Capacitance retention of GSP ternary composite can reach about90%.