The Applications of Metal Oxide and Carbon/Polymer-based Composites in Asymmetric Supercapacitor

• Main Authors: Wen-Jay Liu, 劉文傑
• Other Authors: 鄭紀民
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/51802382348502368236

博士 === 國立中興大學 === 化學工程學系所 === 102 === Increasing the electrochemical efficiency of supercapacitors, which has more potential applications for enhancing the lower conversion of recycle-energy-electron- saved system, is useful to saving-energy and rising up economy of the market. Supercapacitors on lower prices and the stable electrochemical properties of the materials are still worthy of being studied and discussed. The purpose of this study is that modifying or compositing materials for preparing different positive electrode materials of supercapacitors, testing the electrochemical properties and improving the performance of gel electrolyte. Finally, we discuss the electrochemical properties and applicability of the asymmetric supercapacitors. In Chapter 3, nanoscale alloys of nickel and magnesium were synthesized by polyol process. These catalysts were used to form synthesizing multi-walled carbon nanotubes through the thermal chemical vapor deposition process and the activator of nitric acid was used to enhance the specific surface area. Using 5 M of HNO3 to activate carbon nanotubes for 12 hours, the specific surface area increases to 145.29 m2 g-1 (about enhancing 37.5％), and the specific capacitance increases from 8.86 to 22.64 F g-1 (about enhancing 256％) after the modified procedures. In Chapter 4, the three kinds of MnO2 samples which are MO（composites of α-MnO2 and δ-MnO2 types）, HMO（α-MnO2 type）and FeMO（δ-MnO2 type） have been prepared by using sol-gel reaction of fumaric acid and KMnO4 in a mixed alcohol/aqueous solution, and measured the electrochemical properties. The results show that Fe metal is intercalated into MnO2 structure is easy to form δ-MnO2 phase, and specific surface area is improved from 14.5 to 83 m2 g-1. It also can enhance the Na ion adsorption/ desorption of reversibility and capacitance. At the charge/discharge current density of 0.4 A g-1 after 1000 times, the specific capacitance of FeMO sample is still 210 F g-1 and the cycle efficiency is close to 100%. In Chapter 5, the Ni-based nanoparticles supported on graphene nano sheet（GNS） composites have been prepared by using polyol reduction process and fabricated the NiO dispersed layer on Ni metal by thermal treatment process at 250℃ for 1 hour to form the core/shell nanocomposites. The reducing size of particles can improve the activated reactive sites and the thermal treatment can enhance the cyclic stability. The 60Ni-250 sample possesses 385 F g-1 at current density of 1 A g-1 in the potential window of 0 to 0.55 V. In the asymmetric supercapacitor combined with the negative electrode of GNS/Plant Fibber, the energy density can reach up to 21.3 W h kg-1 at a specific power density of 0.8 kW kg-1 in 1 M KOH, and the cyclic efficiency is almost 100% after 50 cycles. In Chapter 6, three kind morphology of MnO2 which are the rod, flake and petal-like type have been prepared by sol-gel reaction, and blending polypyrrole（Ppy） by chemical synthesis as the positive electrode for supercapacitors. The results show that 5% weight ratio of the Ppy blending possesses the well effect of enhancing activated sites. The flake δ-MnO2 as nano-scale two-dimension layered structure provides more surface area than the rod α-MnO2 to approval Ppy and enhances the Faradic effect of the Na ion adsorption/desorption relatively. The samples of AMn5P, DfMn5P and DpMn5P as the electrode materials can get the better electrochemical properties, and show the good cyclic efficiency of 98% after running 1000 times cyclic prolonged test. In Chapter 7, to fabricate the reversed micelles by adding ethylene diamine tetraacetic acid disodium salt dihydrate in ethylene carbonate/ propylene carbonate solution for polymerizing shell-like poly methyl methacrylate（PMMA） in the reverse micelles to control the morphology, size and well dispersed in the liquid phase. The polymeric electrolyte is manufactured by blending PMMA with poly vinylidene fluoride-co-hexafluoropropylene, and the approach simplifies the manufacturing cost and process steps. Wherein the porosity of the sample of M0.5 is 56.43%, the suction rate can reach to 505% and the ionic conductivity is 13.423 mS cm-1. In Chapter 8, we mixed graphene with plant fibers to prepare the graphene/ plant fiber paper with high conductivity and flexibility. The papers are used as the negative electrodes of the asymmetric supercapacitor and tested the electrochemical performance. The Gel electrolyte in Chapter 7 can enhance the potential window voltage up to 2 V and degree voltage up to 3 V. The Ragone plot shows that nickel-based/GNS nanocomposites in chapter 5 have the higher power density output, while manganese-based/Ppy composites in Chapter 6 have high energy density at low power density.