Controlled Synthesis Of Graphene Composites And Their Electrochemical Performances For Supercapacitors

As a new generation energy storage device,supercapacitors have great potential in the fields of information,electronics,transportation and energy.Electrode materials have an important effect on the performance of supercapacitor.An effective way to develop the performance of supercapacitor is to rationally explore and design electrode materials.In recent years,studies in the field of supercapacitor have focused on carbon-based materials,conductive polymer and transition metal oxides,such as activated carbon,glassy carbon,carbon fiber,high-density graphite,foam prepared by polymer pyrolysis,carbon nanotubes,highly-reactived carbon microspheres and graphene,polyaniline,polythiophene,manganese oxides and iron oxides,etc.The transition metal oxides or hydroxides with oxidation-reduction property have high theoretical specific capacitance.In addition,the oxidation-reduction reactions are highly reversible,which helps transition metal oxides and hydroxides to become ideal electrode materials for supercapacitors.However,their low electrical conductivity,easy aggregation,volume effects remain one of the major challenges to be addressed,which would lead to poor cycling stability and irreversible capacity loss.In this study,we report a simple,efficient and facile technology for preparing iron oxides,cobalt oxides,manganese oxides with a diversity of morphologies anchored on the reduction of graphene oxide?rGO?as the supercapacitor electrode materials.X-ray photoelectron spectroscopy?XPS?,X-ray diffraction?XRD?,raman spectroscopy?Raman?,scanning electron microscope?SEM?and transmission electron microscopy?TEM?method are used to analyze the morphology and structure of above-mentioned composites.In addition,electrochemical techniques,such as the galvanostatic charge-discharge at constant current?GCD?,cyclic voltammetry?CV?and electrochemical impedance spectroscopy?EIS?are used to test the electrochemical properties of the composites.The specific research contents and results as follows:?1?The reduced graphene oxide prepared by flame method?FrGO?is compared with the reduced graphene oxide prepared by high temperature annealing?ArGO?and the reduced graphene oxide prepared by hydrothermal method?WrGO?.In order to investigate the chemical and physical properties of the three kinds of reduction reaction products and their electrochemical performance,three electrodes system is assembled.The results show that FrGO has the best performance of supercapacitor.?2?A novel?-Fe₂O₃ anchored on reduced graphene oxide composite??-Fe₂O₃/rGO?is synthesised by flame method.The structural and morphological characteristics of the obtained composites are investigated.The results show that pyramid-type?-Fe₂O₃ is anchored on reduced graphene oxide evenly.The electrochemical measurement results show?-Fe₂O₃/rGO containing the GO mass ratio of 50%in precursors can achive high specific capacitance up to 385 F g^-1at current density of 0.5 A g^-1.?3?CoO nanoparticles about 20 nm anchored stably on the reduced graphene oxide?CoO/rGO?are synthesised by electrostatic adsorption and flame method.The obtained composite is characterized and tested,and the results show that the CoO/rGO has a large specific surface area and excellent electrical conductivity.Owning to the characteristics,the composite exhibits ultrahigh specific capacitance,outstanding cycling stability and good rate performance.?4?Mn₃O₄ nano-sheet anchored on reduced graphene oxide?Mn₃O₄/rGO?is synthesised by electrostatic adsorption and flame method.The morphological characterization show that the Mn₃O₄ nano-sheet was evenly distributed on the reduced graphene sheet.The strong interaction between graphene layers and Mn₃O₄ nanosheet could provide much active site to Farada redox reaction and have excellent electrical conductivity.Mn₃O₄/rGO used as electrodes in supercapacitor exhibits specific capacitance and outstanding cycling stability(85.47%of its initial value after 10,000cycles at a current density of 10 A g^-1).?5?Bimetallic oxides/reduced graphene composite?CoMn₂O₄/rGO?is synthesised by electrostatic adsorption and flame method.As can be seen from the SEM images,CoMn₂O₄ nano-particles are attached to the reduced graphene oxide sheet closely,which provides large surface area and much active site to Farada redox reaction.The electric performance test shows the optimized CoMn₂O₄/rGO composite exhibits high specific capacitance(1527 F g^-1)and excellent cycling stability?90.4%retention after2,000 cycles?in aqueous solution,demonstrating excellent electrochemical performance.In this study,an efficient and simple route is designed to reduced graphene oxides,and four new composite materials??-Fe₂O₃/rGO,CoO/rGO,Mn₃O₄/rGO and CoMn₂O₄/rGO?.We mainly focus on the large-scale preparation of graphene composites and try to explore their application.The four new composites used as supercapacitor electrode exhibit excellent electrochemical properties through the test and performance analysis.The above research results provide a theoretical basis for large-scale preparation of graphene composites and a reliable idea for the development,utilization of different graphene composites as energy storage devices and lay a practical foundation for further exploration of high-performance supercapacitors in the future.