الفهرس 
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Abstract
The rapidly growing interest for flexible energy storage systems has tempted researchers to develop new materials that can store a large amount of energy. Carbon Nanofibers (CNFs)-based materials have been the subject of broad exploration from the perspective of energy storage because of its unique ability to trap charges coupled with its favorable electronic conductivity, high aspect ratio along with a very high specific surface area. This was also accompanied by an outstanding intrinsic double-layer capacitance, excellent mechanical flexibility, and environmental stability as well. This thesis work is related to explore and build up new approaches for further enhancing the performance of stand alone CNFs based electrodes that can be effectively used to fabricate high-performance and flexible supercapacitors devices. The thesis is divided into three main parts related to the approaches employed to improve the electrochemical performance of CNFs electrode and boost the specific capacitance of the fabricated CNFs -based devices. The First section of this thesis is dedicated to develop and characterize a new all-carbon design for free-standing interconnected CNFs electrodes for supercapacitors application. The fibers are obtained via carbonization of three components electrospun nanofibers mats based on polyacrylonitrile (PAN) polymer, as a carbon backbone precursor, polyvinyl alcohol (PVA), as a sacrificial copolymer, and 0-1.0 wt.% multi-walled carbon nanotubes (MWCNTs). Carbonizing the fibers made from these ternary composites resulted in CNFs with about two times larger in surface area and one order of magnitude higher in electrical conductivity compared to those obtained by the carbonization of neat polyacrylonitrile and binary polyacrylonitrile 0-1.0 wt% carbon nanotubes mats. Carbonized polyacrylonitrile-polyvinylalcohol-0.3 wt% carbon nanotubes mat also attained the highest surface area and significant improvement capacitive performance was also achieved. Therefore, this new design offers a potential free-standing carbon nanofibers electrode for future supercapacitor devices fabrication. In the second section, three hierarchical hybrid nanostructures composed of nickel oxide (NiO), cobalt oxide (Co3O4), and nickel cobalt oxide NiCo2O4 nanoparticles and ultra-thin nanosheets on standalone carbon nanofibers (CNFs) electrode are controllably synthesized through hydrothermal method. The metal oxide nanostructure has been controlled by changing the concentrations and the ratios of the metal salt in the procurer solution. The electrochemical performance of the three nanostructured hybrid electrodes is systematically studied. The three hierarchical hybrid nanostructured electrodes exhibited high capacitance and excellent cycling stability compared to the blanked electrodes. The remarkable electrochemical performance will undoubtedly make these hybrid structures attractive for high-performance supercapacitors with high power and energy densities. The third section is discussing the asymmetric electrode approach that has been used to improve the electrochemical performance by widening the potential window of the supercapacitor device. Well-uniformly distribution of NiCo2O4 nanorods anchored on CNFs was successfully synthesized by in-situ growth under hydrothermal process and used as the positive electrode. Whereas, the negative electrode comprises from an activated multichannel carbon nanofibers (AMCNFs) that were fabricated by the electrospinning and followed by alkaline activation. CNFs superior to its symmetric supercapacitor counterpart, a very high energy density of 38.5 Wh/kg at maximum power density of 1.6 kW/kg was achieved from the well fabricated asymmetric device.