Preparation Of Graphene/anthraquinone Composites And Their Performance

As a new type of energy storage, supercapacitors storage energy using either ion adsorption or fast surface redox reactions, with their high power density and long cycle life. They can complement the batteries and normal capacitors in electrochemical energy storage and applications, realizing their potential in the areas of aerospace, automobile, military, medical treatment and electronic portable equipments. Electrode materials are key to the performance of supercapacitors. Combining materials with double-layer capacitance and pseudocapacitancehas complementary advantages and could improve the properties of composites. Graphene, with large specific surface area, good mechanical and physical and chemical properties, is suitable for working as a substrate. Anthraquinone possesses redox-active quinone group and high theory specific capacitance, with a tunable structures.There have beenreported some researches on anthraquinone working as supercapacitor electrodes. In this work, graphene was chosen as substrate to prepare graphene/ 1,5-diaminoanthraquinone(DAA) composites, and factors which could influenced the polymerization of poly(1,5-diaminoanthraquinone)(PDAA) were studied.Reduced graphene oxide(RGO) /PDAA were prepared by in-situ polymerization, and the morphologies, structures and electrochemical properties of the samples were also analyzed.Hydrothermal was used to prepare RGO/DAA composites, different ratio of RGO/DAA were prepared by controlling the mass ratio of RGO and DAA. The morphologies and structures of composites were investigated by Field-emission Scanning Electron Microscopy(FESEM), Fourier Transform Infrared Spectroscopy(FTIR), X-ray Diffraction(XRD), Raman spectra. Electrochemical performance was studied by Cyclic voltammetry(CV), Galvanostatic charge-discharge(GC), Electrochemical impedance spectroscopy(EIS) and cycle ability test. Results showed that for the RGO/DAA composites, with the increasing addition of DAA, specific capacitance increases firstly then decreases.When the mass ratio of RGO and DAA is 5 to 1, specific capacitance reaches a maximum value of 196 F/g at current density of 0.1 A/g, it also shows good rate ability and cycle ability. In order to improve the performance of RGO/DAA, RGO was replaced by active Microwave Exfoliation Graphene Oxide(aMEGO) to prepare composites. Unfortunately, the addition of DAA can not improve the electrochemical properties of composites, even poorer than aMEGO, which may caused by the decrease of specific surface area after DAA was added into aMEGO, thus faradic capacitance generate from DAA contributes less than the loss of double-layer capacitance induced by the damage of the structure, leading to the declination of the performance. DAA behaves differently in different substrates indicates that selecting appropriate carbon material as substrate is important to fully realize its potential application.On the basis of hydrothermal reaction, physical blending and chemical grafting were utilized to prepare RGO/DAA. The morphologies and structures of the composites prepared in different ways were studied and their electrochemical properties were also analyzed. Results show that RGO/DAA prepared by chemical grafting exhibits the best comprehensive electrochemical performance, with a maximum specific capacitance of 234.3 F/g at 0.1 A/g.When current density increased to 2 A/g, its specific capacitance retains 57.3%, and after 1000 cycles, it keeps 87.1% of the original value.PDAA was polymerized through chemical oxidation,varying the polymerization conditions such as oxidant, solvent, reaction time, temperature, ratio of monomer and oxidant to investigate the optimum polymerization condition.The obtained PDAA showed a good electrochemical property, when chromiumtrioxide as oxidant, 1 M H2SO4/DMAc as solvent, molar ratio of DAA and oxidant is 1 and the reaction conducted at 20 ℃ for 24 h.Besides, redox-active quinhydrone was added into electrolyte to improve the performance. There are obvious redox peaks in the test curves and the specific capacitance can be improved. More importantly, it can enlarge the potential window, which is beneficial to improve energy density of supercapacitor. However, a poor rate ability was obtained with the addition of quinhydrone.RGO/PDAA composites were also prepared by in-situ polymerization to overcome the low conductivity of PDAA. It showed that the surface of RGO was covered with PDAA particles, and with the increasing ratio of DAA to RGO, accumulation of PDAA can be observed. Among the composites, RGO/PDAA(1:4) has a higher specific capacitance and good rate ability and cycle ability, while it seems no synergetic effect between RGO and PDAA. In-situ polymerization can not embody advantages of both components, maybe another method should be considered to make full a use of RGO and PDAA.