Controlled Synthesis Of Carbon Nanofibers And Their Electrochemical Performance

Carbon nanofibers (CNFs) have attracted intensive attention worldwide, due to their promising potential applications in catalysis, adsorption, energy storage and conversion, etc. So far, researchers have made great progress in synthesis, functionalization, and application of carbon nanofibers. However, how to precisely design and synthesize porous carbon nanofibers with tunable porosity and well-defined structure is still a great challenge. In this thesis, based on the research background of carbon nanomaterials in our group, we have developed the designed synthesis and electrochemical application of porous carbon nanofibers, described as follows.(1) We have synthesized series of nanosized polymer materials including nanospheres, nanorods and nanofibers, which were fabricated via hydrothermal approach by using surfactant F127as shape-directing agent and resorcinol and hexamethylene tetramine (HMT) as carbon precursor. The nanostructures and morphologies of as-synthesized polymer nanomaterials can be simply tailored by changing the concentrations of F127and HMT and hydrothermal conditions. Nanostructured carbon materials with different morphologies can be obtained after carbonization and activation of the resin polymer counterparts.(2) By careful control of the carbonization and steam activation conditions, the BET surface area and total pore volume of the final porous carbon nanofibers can be tuned in the range of529-1144m2g-1and0.284-0.666cm3g-1, respectively. The activated carbon nanofibers can be used as supercapacitor electrode, whose specific capacitance can be up to283F g-1at the scan rate of5mV s-1. Meanwhile, the Li-S batteries composed of microporous carbon nano fibers-encapsulated sulfur structure exhibit unprecedented electrochemical performance with high specific capacity and good cycling stability, i.e.,950mA h g-1after50cycles of charge/discharge. The excellent electrochemical performance of CNFs is attributed to their high-quality fiber morphology, proper porous structure, large surface area, and good electrical conductivity.(3) In order to improve the dispersibility and pore connectivity of as-reported carbon nanofibers, colloidal mesoporous carbon nanofibers can be obtained through confined nanospace pyrolysis. These carbon nanofibers can be synthesized by confined nanospace pyrolysis of their polymeric precursors. Distinctively, such process leaves out the need for grind and mixing steps. The supercapacitor electrodes which are fabricated via a simple dipping and rinsing approach exhibit a reversible specific capacitance of206F g-1at the current density of5A g’in6.0mol L-1aqueous KOH electrolyte. Porous carbon nanofibers are regarded as essential components of high-performance energy storage devices in the development of renewable and sustainable resources, due to their high surface areas, tunable structures, and good conductivities. The results show that the carbon nanofibers represent an alternative promising candidate for an efficient electrode material for energy storage and conversion.