Study On The Synthesis And Electrochemical Capacitance Performance Of Quasi Graphene-based Nanocomposites

The multi-walled carbon nanotubes can be split along the longitudinal directionto form carbon nanomaterials which are similar to graphene nanoribbon by usingmodified Hummers method. This quasi graphene material combines the advantages ofgraphene and carbon nanotubes, not only avoids the preparation of grapheneirreversible agglomeration but also makes specific surface area relative to carbonnanotubes be greatly improved, which has a very important research value insupercapacitors application. The high resistivity of pure carbon materials reduces thecapacitive properties. In order to solve this problem, it is more focused on the study ofmetal oxides, conductive polymer or composite with other carbon nanomaterials toform three-dimensional nanocomposite materials to improve electrochemicalcapacitance properties. In this thesis, we mainly focus on the study of quasi graphene-metal oxides and quasi graphene-reducd graphene oxide to improve theelectrochemical capacitive performance of quasi graphene. The main results obtainedare as follows:(1) Multi-walled carbon nanotubes (MWCNTs) were split along the longitudinaldirection to form quasi graphene oxide (QGO) by modified Hummers method andquasi graphene nanosheets/RuO2(QGN/RuO2) composites with40.0wt.%RuO2loading were prepared by a one-step hydrothermal synthesis without any reducingagent. The characterization of morphology and structure shows that the amorphousRuO2nanoparticles are uniformly dispersed on all the surfaces of QGN. Theelectrochemical measurements show that the QGN/RuO2composites exhibit betterelectrochemical capacitive properties than pure RuO2and pure QGN in acidic,alkaline and even in neutral electrolytes. The specific capacitances of QGN/RuO2in1M KOH,1M H2SO4, and1M Na2SO4are453.7,415.7,287.5F g-1. Significantly, theQGN/RuO2composites can achieve a high voltage window of1.6V and greatlyincrease the energy density (102.2W h kg-1) and power density (1600W kg-1) ofsupercapacitors in1M Na2SO4(1A g-1). These results demonstrate that theQGN/RuO2composites are a promising material for high-performancesupercapacitors.(2) Quasi graphene nanosheets/MnO2(QGN/MnO2) composites have beenfabricated by using a facile physical mixing method. The prepared composites were characterized by means of X-ray diffraction (XRD), Fourier transform infraredspectroscopy (FTIR), Scanning electron microscopy (SEM). Electrochemicalperformances are evaluated using cyclic voltammetry (CV), galvanostaticcharge-discharge. The results show that the ratio of MnO2to QGN in compositematerials has significant influence on the electrochemical performance of composites,the optimum mass ratio is5:5. We have achieved the maximum specific capacitance of319.2F g1at a scan rate of5mV s-1in1M H2SO4aqueous solution. Additionally,QGN/MnO2composites exhibit the highest energy density of19.4Wh kg1at powerdensity of80W kg1and excellent capacitance retention with no more than7%capacitance loss after1000cycles at the most favorable composites ratio.(3) A convenient hydrothermal co-reduction method was used to synthesizethree-dimensional quasi graphene nanosheets/reduced graphene oxide (QGN/RGO)composites. The QGN intercalated between RGO, not only increased the specificsurface area of QGN and inhibited the aggregation of RGO, but also enhanced thesurface area utilization of both them. Therefore, the prepared QGN/RGO compositematerials can greatly improve the electrical conductivity and electrochemicalcapacitance properties. The electrochemical measurements show that the hybridmaterial exhibits good synergistic effect leading to higher capacitance compared witheither RGO or QGN alone. The maximum specific capacitance of705F g-1wasachieved at1A g-1. Moreover, the satisfactory cycling stability is also obtained.