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Fabrication and Investigation of Supercapacitors Based on Graphene Nanocomposites

Jokar, Effat | 2014

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 46932 (48)
  4. University: Sharif University of Technology
  5. Department: Institute for Nanoscience and Nanotechnology
  6. Advisor(s): Iraji Zad, Azam; Shahrokhian, Saeed
  7. Abstract:
  8. Development of renewable energy production from sun and wind and the development of hybrid electric vehicles seem to be integral components in modern societies in order to overcome the environmental pollution and reduce the use of fossil fuel sources. In such devices energy storage plays an important role and supercapacitor is one the important energy storage devices. Structure of supercapacitor electrodes has considerable effect on supercapacitor performance. Graphene as a 2D carbon structure can improve electrochemical properties of electrodes. Here three different hybrid structure of graphene have been realized. The high capacitance and cyclic stability of graphene nanosheets decorated with Co3O4 nanoparticles as a material for supercapacitor electrodes are synthesized. Hydrothermal method is adopted to deposit cobalt oxides on the reduced graphene oxide (RGO) sheets in a mixture of water and dimethylformamide (DMF) as the solvent with different volume ratios. The water volume ratio presents a crucial factor in the nucleation and growth process. Electrochemical measurements indicate that water volume ratio in the mixture solvent influences on capacitance of the RGO/Co3O4 composite electrodes. The highest obtained specific capacitance is 440.4 Fg-1 with 50% volume ratio of water at current density of 5 Ag-1. A novel and facile procedure for functionalization of graphene with some electroactive molecules is presented. The graphene has been functionalized by catechol-based molecules, which are electroactive molecules with electrochemically reversible properties. The functionalized graphene exhibits very effective pseudocapacitor behavior for charge storage. As a result, the functionalized graphene sheets show a reversible electrochemical behavior and can be used as pseudocapacitor electrodes with an excellent stability. The electrochemical results of the prepared electrodes reveal rather high specific capacity of 288 F g-1 at a high current density of 28 A g-1, which shows remarkably enhanced performance for supercapacitor applications. A high rate capability supercapacitor based on fluorine-doped graphene-carbon nanotubes aerogel network (FG-CNT) are fabricated. Based on the electrochemical impedance spectroscopy data, fluorination decreases the charge resistance of graphene sheets while CNTs act as spacer in the 3D structure both improved the electrochemical properties of the resulted aerogel. Based on the Fourier transform infrared spectroscopy, these excellent performance is related to semi-ionic bonds between fluorine and carbon. The specific capacitance of graphene aerogel drops 78% when discharge current increases from 2 to 40 mA, while the G-CNT and G-CNT-F electrode loses 63.8 and 33.3 % of its specific capacitance, respectively
  9. Keywords:
  10. Supercapacitor ; Catechol ; Pseudocapacitor ; Graphene ; Hybrid Supercapacitor ; Cobalt Oxide

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