Loading...

Using of Oxides, Hydroxides and Sulfides of Some Transition Metals and Carbon Nanostructures in Supercapacitors

Mohammadi, Rahim | 2018

993 Viewed
  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 51344 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Shahrokhian, Saeed
  7. Abstract:
  8. Electrochemical capacitors are type of electrical energy storage devices that research on them has grown due to the development of hybrid vehicles. It is proved that lectrodes configuration has vital role in electrochemical capacitors performance. In this thesis, transition metal hydroxides, oxides and sulfides along with carbonaceous materials have benn used as active materials in supercapacitors. In first section, graphite has been poroused by applying anodic potential of 2V in acidic electrolyte which results in exfoliation of graphite planes due to gas diffusion to the interlayer of graphite sheets. The prepared porous graphite was used as precursor for electrodeposition of nickel hydroxide nanostructures. Results revealed that porous graphite could be suitable candidate for electrodeposition of nickel hydroxide nanostructures. Electrodeposition of nickel hydroxide structures has been done for different periods between 100 and 700 s and the electrode which prepared at time of 500 s showed the highest areal capacitance of 5.2 F cm−2 at a current density of 2 mA cm−2. Graphene oxide nanosheets have been synthesized by modified Hummer’s method and used with nickel ions in a one-step electrochemical co-deposition. Electrochemical measurements indicate that potential scan rate influences the capacitance of the ERGO/NiO composite electrode. The highest specific capacitance was 1715.5 Fg-1 at current density of 2 Ag-1 and obtained for composite electrode prepared at scan rate of 200 mV s-1. However, the composite electrode showed specific capacitance of 1066.7 F g-1 at very high current density of 40 A g-1 which demonstrates high ratability of the composite electrode. In third work presented, we used corrosion charateristics of transition metals for formation of active sites on the transition metal surface in hydrothermal conditions in acidic media. Then, the active sites which really fabricated by dissolution of copper in acidic media at nearly high temperature and pressure, converted to copper oxide nanosheets by electroactivation in alkaline solution. Results demonstrated that both hydrothermal media and also the time of hydrothermal treatment have significant effect on the performance of CuO electrodes. Highest specific capacitance of 125.4 mF cm-2 was obtained in alkaline electrolyte for electrode prepared at 110 ºC and in HCl solution as hydrothermal media. Last part of the thesis, incleds preparation of ternary dendritic transition metal (Ni-Co-Cu) using H2 as hydrodynamic template by applying cathodic potential in acidic media. Then, the prepared ternary dendritic transition metal was converted to their corresponding tetranary dendritic transition metal sulfides by direct sulfidization in thiourea in hydrothermal conditions. The tetranary dendritic transiton metal sulfides have been used as cathode material in supercapacitors. For negative electrode, electro-etched carbon fiber has been used. Etching of carbon fiber electrode has been done in mixed solution of concentrated HNO3:H2SO4 (v: v ,1:1) by applying anodic potential of 5V. Finally, an asymmetric supercapacitor (ASC) cell was fabricated with dendritic sulfide structures as cathode and electro-etched carbon fiber as anode which showed large potential window of ~1.6 V with good rate capability and rate performance in alkaline media
  9. Keywords:
  10. Supercapacitor ; Carbon Nanomaterials ; Pseudocapacitor ; Transition Metal Oxides ; Hybrid Supercapacitor ; Porous Media ; Electrical Double Layer Supercapacitor ; Transition Metal Hydroxide ; Transition Metal Sulfide

 Digital Object List

 Bookmark

No TOC