Electrophoretic Deposition Of Graphene-based Composites And The Electrochemical Performance Of Supercapacitor Electrode Materials

Supercapacitor is a new type of energy storage device between the traditional capacitor and the secondary battery.Due to the advantages of high power density,good cycle life and so on,the supercapacitor shows great potential in the field of green chemical power supply.It is probably the next generation Important energy storage devices,in which the electrode material is one of the main factors that determine the performance of the capacitor.In this paper,three-dimensional reduced graphene oxide?RGO?electrode materials were prepared by electrophoretic deposition and thermal reduction method.The morphology of the deposited graphene oxide?GO?was investigated by scanning electron microscope?SEM?.The low deposition voltage was applied?less than 60 V?,the frameworks in nickel foam were not covered with GO completely.The deposition voltage was too higher?higher than 60 V?,some gaps among the frameworks were sealed due to excess growth of GO.The thermal reduction effect at different temperatures was studied by X-ray diffraction?XRD?,Raman,Fourier transform infrared spectroscopy?FTIR?,thermal gravimetric analysis?TGA?and differential thermal analysis?DTA?.The oxygen-containing functional groups in GO were removed efficiently when GO was thermally reduced at 300°C,which contributed to the enhancement in electrical double layer capacitance.At the same time,some oxygen-containing functional groups in GO were maintained,which was beneficial to the increase in pseudocapacitance.The electrochemical properties of the prepared electrodes were investigated by cyclic voltammetry?CV?and galvanostatic charge-discharge test.The results showed that the highest specific capacitance of RGO was obtained when the deposition voltage was 60 V and the thermal reduction temperature was 300°C.The specific capacitance values calculated by CV and galvanostatic charge/discharge were 139 F·g^-1(0.005 V·s^-1)and 151 F·g^-1(1 A·g^-1),respectively.The specific capacitance of RGO still maintained 55%and 66%of the initial value when the scan rate and the current density were increased up to 0.3 V·s^-1 and 10 A·g^-1,respectively.RGO also displayed an excellent cycling stability with by maintaining 98%of the initial specific capacitance after 500 cycles.On this basis,a three-dimensional MnO₂/RGO composite electrode was prepared by a two-step method.At first,the RGO electrode was prepared by electrophoretic deposition and thermal reduction.The RGO was obtained when the deposition voltage was 60 V and the thermal reduction temperature was 300°C,and then the MnO₂ was deposited by a constant voltage of 0.6 V.The XRD,SEM,Transmission Electron Microscope?TEM?and Raman results showed that a layer of MnO₂ with high qualigy can be obtained at the deposition voltage of 0.6 V.Moreover,combined with CV and galvanostatic charge-discharge test of electrochemical methods to study its electrochemical properties.The specific capacitance values calculated by galvanostatic charge/discharge was 432 F·g^-1(1 A·g^-1).The specific capacitance of MnO₂/RGO/NF still maintained 55%of the initial value when the current density was increased up 10 A·g^-1.MnO₂/RGO/NF also displayed an excellent cycling stability with by maintaining 97.5%of the initial specific capacitance after 500 cycles.