Reactable Ionic Liquid Assisted Solvothermal Synthesis Of Iron Family Metal Oxide Composites And Their Electrochemical Performances

The growing environmental pollution and oil resource shortage have spurred the scientists to study and develop new energy storage devices replacing the traditional internal combustion engine. Due to high output power, fast charge/discharge rate, high cycle efficiency and long life, electrochemical supercapacitor with characteristics of ordinary capacitors and chemical batteries simultaneously, has attracted worldwide research interests and become an investigation focus since its birth. Of various influence factors on the performance of electrochemical capacitor, the electrode material is the most important, which directly determines the production cost and performance of the resulting supercapacitor. Carbon materials have been the ideal candidates for electrode materials, because of the advantages of rich in resource,lower cost, higher specific surface area, simpler preparation method, non-toxic, higher specific surface area, higher conductivity, better chemical stability and wider temperature range and so on. At the same time, transition metal oxides and hydroxides are relatively good redox pseudocapacitor electrode material, because their different oxidation states can provide more possibility of charge transfer. Therefore, the relate study has also been becoming a research hotspot in recent years. Especially, abundant,cheaper iron, cobalt and nickel oxides with high theoretical specific capacitances have been attracting the attention of many researchers.The current research hot spot in preparation of supercapacitor electrode materials is mainly focused on the composition of the carbon based materials and metal oxides to take full advantages of the components and the synergistic effect. Through decreasing the particle size, increasing the specific surface area, improving the porosity, preventing particle from agglomeration, improving the electronic and proton transfer, increasing the active sites, enlarging the voltage window, improving circulation stability and providing the pseudocapacitance so as to improve the electrochemical properties.In this thesis, some reduced grapheme(rGO) based and grapheme like carbon nitride(g-C3N4) iron based cobalt oxide composite materials were prepared by a solvothermal method and their structures, morphologies and electrochemicalproperties were studied using thermogravimetric analysis(TG), infrared spectroscopy(FT-IR), X-ray diffraction(XRD), field emission scanning electron microscope(SEM), cyclic voltammetry(CV) and constant current charge and discharge technology(GC). The main contents are as follows:1. The operation principles of electrochemical capacitors and main investigation techniques were introduced and the current progress on the electrode materials was reviewed.2. Using graphite oxide and CoCl2·6H2O as raw materials, a Co3O4/rGO(IL)composite material was successfully by a ionic liquid(IL) assisted solvothermal method through in situ growth of Co3O4 nanoparticles on reduced graphene oxide and influence of the addition amounts of graphene oxide on the electrochemical properties of the resulting electrode materials was studied. The morphology of the prepared composite material showed that it had a hierarchical broccoli–like structure where Co3O4 microspheres consisted of quantities of nanoparticles were immobilized on reduced graphene oxide. The composite material exhibited a good electrochemical performance, when the current density of 1A·g-1, its specific capacitance reached321.9 F·g-1. What is more, when the current density was increased to 5A·g-1the specific capacitance was still maintained to a higher value of 161.0 F·g-1, indicating this material had a good application potential.The results still indicated that the presence of ionic liquid remarkably improved the electrochemical properties of the resultant electrode material. The ionic liquid not only served as precursor supporter, but also as dispersing agent and template in the synthesis reaction, which effectively controlled the formation of the particular structure and played an important role to improve the electrochemical performance of the prepared material.3. Two kinds of the supercapacitor electrode materials Fe2O3/g-C3N4(IL) and Co3O4/g-C3N4(IL) were prepared using solvothermal method through compositions of hematite and cobalt oxide with graphite-like carbon nitride and their structures,morphologies and electrochemical properties were studied in detail. It was indicated that Fe2O3/g-C3N4 composite material showed a loose spherical structure in which g-C3N4 was coated by Fe2O3 nanoparticles and Co3O4/g-C3N4(IL) had a laminatedstructure of g-C3N4 sheets deposited Co3O4 nanoparticles. The results showed that these two kinds of composition materials possessed good electrochemical performance, and when the current density was 1A·g-1 their specific capacitances respectively reached 258.7 F·g-1 and 195.8 F·g-1 that were higher than those obtained in absence of the ionic liquid.The solvothermal synthesis procedure proposed in the thsis for preparing electrode materials was simple and convenient method very suitable for mass production.