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Preparation and Investigations of Flexible Supercapacitors Using Nanocomposites with Graphene-based Structures and Layered double hydroxide Ni/Co and Manganese Molybdate

Mehrabi Matin, Bahareh | 2019

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 52224 (48)
  4. University: Sharif University of Technology
  5. Department: Institute for Nanoscience and Nanotechnology
  6. Advisor(s): Shahrokhian, Saeed; Iraji-zad, Azam
  7. Abstract:
  8. In the first part of this research, for the first time, we introduced a flexible high performance graphene-based supercapacitor using silver fiber fabric as the current collector. The silver fiber fabric offers remarkable advantages such as light weight, mechanical flexibility and ease of integration with electronic textiles, which well-suited for wearable energy storage devices. A new hybrid material of graphene-silver fiber fabric (rGO/SFF) was prepared through a facile electrophoretic deposition of graphene and being used as a binder-free flexible supercapacitor electrode. In order to obtain the optimum condition, the effect of deposition time was investigated and a duration time of 10 minute was selected as an optimum condition. The as-prepared electrode based on rGO/SFF-10 showed excellent electrochemical performance in the three-electrode configuration using KOH (3 M) as the supporting electrolyte, with the highest capacity of 172 mF/cm2 at 4 mA/cm2 and a capacitance retention of 97% after 5000 charge_discharge cycles. The results suggest that the prepared electrode is a promising candidate for wearable energy storage applications.In the second part of this research, we have developed a flexible asymmetric supercapacitors (ASCs) using NiCo-layered double hydroxide (NiCo LDH) supported on three-dimensional nitrogen-doped graphene (NG) as a positive electrode material and NG as a negative electrode material. Highly conductive NG provides facilitate the (dis)charging of NiCo LDH deposited on it. The NiCo LDH@NG/CC composite electrode exhibited a high specific capacitance of 1421Fg−1 at a current density of 2 A g−1. The fabricated flexible ASC device shows a specific capacitance of 109 F g-1 at 0.5 A g-1 and a maximum energy density of 49 W h kg-1, which is comparable with or superior to previously reported electrodes based on nickel-cobalt hydroxides. Under repeated mechanical bendings, the ASC demonstrates high bending stability up to 450 bending cycles at 90o angle.In the third part of this research, we have reported for the first time, preparation of nitrogen and sulfur co-doped activated carbon (NSC) by one step pyrolysis using thiourea as nitrogen and sulfur sources. NSC material in combination with Mn and Mo precursors was used for synthesis MnMoO4/NSC composite as supercapacitor electrode material. The as-prepared composite in the three-electrode configuration using 0.5M Na2SO4, showed a high specific capacitance of 122 F g-1 at 0.5 A g-1, which displayed remarkable improvement over the NSC (94 F g-1) and MnMoO4 (19 F g-1). Such better electrochemical behavior of MnMoO4/NSC attributed to the higher conductivity of the NSC material. Furthermore, the presence of trivial amounts of N and S groups can effectively improve the surface wettability of the MnMoO4/NSC electrode in the aqueous electrolyte, which can enhance the capacitance performance of the MnMoO4/NSC electrode relative to the other electrodes. A symmetric supercapacitor device was assembled from two same MMoO4/NSC electrodes and showed 37 F g-1 at 0.5 A g-1
  9. Keywords:
  10. Supercapacitor ; Graphene ; Flexibility ; Nickel/Cobalt Layered Double Hydroxide ; Manganese Molybdate ; Nitrogen and Sulphur Co-doped Activated Carbon ; Silver Fiber

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