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URN etd-0910115-150835 Statistics This thesis had been viewed 820 times. Download 0 times. Author Shu-Wei Chou Author's Email Address No Public. Department Chemical Engineering Year 2014 Semester 2 Degree Ph.D. Type of Document Doctoral Dissertation Language English Page Count 165 Title Electrodeposition of metal sulfides as cathode material for hybrid supercapacitors Keyword Hybrid supercapacitor Cathode Cobalt sulfide Nickel sulfide electrodeposition Pulse-reversal deposition Pulse-reversal deposition electrodeposition Nickel sulfide Cobalt sulfide Cathode Hybrid supercapacitor Abstract In recent years, nanostructure metal sulfides have been widely employed as electrode materials in hybrid supercapacitors (SCs) due to their high specific capacity and excellent electrochemical stability. Generally, the metal sulfides are usually prepared by using chemical method, such as chemical precipitation and hydrothermal methods. However, the metal sulfide powders still need polymer binder, conducting agent and high pressure coating on the conductive substrate, which could contribute extra contact resistances.
In the chapter 3 of this thesis, metal sulfides (cobalt sulfide and nickel sulfide) were successfully deposited on Ni foam substrates by the facile potentiodynamic (PD) deposition method. The CoS and Ni3S2 electroactive materials delivered remarkable specific capacity up to 224.7 mAhg-1 at 4 A g-1 and 99.6 Fg-1 at 2 Ag-1, respectively. Moreover, the CoS electrode exhibited about 100% retention of specific capacity around and 99% Columbic efficiency after consecutive 1000 cycles with a fairly high current density of 8 A g-1.As for the Ni3S2 flaky electrode, it can still possess specific capacity retention around 91% after cycling of 500-1000 cycles at a high current density of 4 Ag-1.
In the chapter 4 of this thesis, the corresponding deposition mechanism of metal sulfides has been investigated by using cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS). The CV results suggested that the partial metal (M=Ni2+, Co2+) ions complexes with the electroreduced product of TU in the form of [MTU]2+ and the formation of electroreduction of [MTU]2+ complexes onto the Ni foam surface. Then the [MTU]2+ would further reduce to MS onto the Ni foam surface. In order to comprehend the electrodeposition mechanism of MS, the XPS analyses were carried out the results.
The Ni3S2 is successfully prepared on a Ni foam substrate by the proposed potentiodynamic, the required power-supply equipment for the PD deposition is relatively expansive. It would be unfeasible for practical applications. Therefore, the pulse reversal deposition technique have been developed to prepare Ni3S2 electrode in the chapter 5 of this thesis. The NSPR-2 electrode delivered remarkable specific capacity up to 179.5mAhg-1 at 2 A g-1 and 105.9 mAhg-1 at 32 A g-1 charge–discharge current density in 1.0 M KOH aqueous electrolyte. Furthermore, a hybrid SC with the flaky Ni3S2 as the positive electrode material and carbon fiber cloth (CFC) as the negative electrode, exhibited a high energy density (26.4 W h kg−1) at an power density of 1978 W kg−1.
Advisor Committee Jeng-Yu Lin - advisor
Chao-Hong Wang - co-chair
Chiung-Cheng Huang - co-chair
Fu-Ming Wang - co-chair
Tsung-Wu Lin - co-chair
Wen-Ching Shih - co-chair
Files Date of Defense 2015-07-17 Date of Submission 2015-09-10