Study Of FeO_x/N_y Composite Electrode Materials-based Supercapacitors

Enter twenty-first century, the traditional fossil energy resources are being exhausted and the problems of energy shortages and environment deterioration are increasingly serious. Therefore, new renewable clean energy, such as solar energy, nuclear energy, tidal energy etc., is regarded as alternative energy. Meanwhile, the solution to the high-efficiency storage of the green sustainable energy is becoming an important topic of the global research. Supercapacitors, also called electrochemical capacitors, arouse researchers’great concern in recent years due to its high power density, long cycle life and wide working temperature. Moreover, electrode material plays a crucial role in supercapacitors. Among the various electrode materials, metal oxides/metal nitrides are considered as the most promising materials due to the high capacitance. Composited with carbon materials, it can effectively improve the electrical conductivity, electrochemical properties and cycling performance of metal oxides/metal nitrides.In this thesis, iron-based composite fibers with different morphology, such as Fe2O3 nanofibers, FeO3-C nanofibers and FexNy-C nanofibers, were prepared by electrospinning and their electrochemical performances were measured. We proposed and developed a kind of excellent electrode material by controlling the morphology and composition of iron-based fibers. The main contents in this paper are summarized as follows:1. Fe2O3 nanofibers were prepared by electrospinning method and subsequent heat treatment process. The morphology, structure and electrochemical property of Fe2O3 nanofibers were influenced by iron source quality and heat treatment temperature. The results indicate that Fe2O3 fibers with 3D structure (600℃,0.6 g Fe(acac)3) shows a specific capacitance of 244.6 F/g under the scan rate of 5 mV/s.2. Fe2O3-C nanofibers were prepared by electrospinning method and a series of improved heat treatment process under N2. The influence of different ratio of Fe(acac)3 to PVP K90 on the structure, morphology and electrochemical performance of Fe2O3_C nanofibers were studied. When the ratio of Fe(acac)3 to PVP K90 is 6:17, Fe2O3 are distributed evenly on the Fe2O3-C fiber surface, which resulted in a better electrochemical performance (Csp=373.2 F/g, at 5 mV/s) than that of pure Fe2O3, due to the combination of double layer capacitance and pseudocapacitance.3. FexNy-C nanofibers were prepared by electrospinning method and a series of heat treatment under NH3 gas atmosphere. The influence of heat treatment temperature on the component, structure, morphology and electrochemical performance of FexNy-C composite nanofibers were studied. The research shows that since FexNy are distributed evenly on the fiber surface, the FexNy-C nanofibers exhibits the most significant electrochemical performance (Csp=560.8 F/g, at 5 mV/s) at 700℃, which is much better than pure Fe2O3 nanofibers and Fe2O3-C nanofibers.