| Climate change and the limited availability of fossil fuels have greatly affectedthe world economy and ecology. With a fast-growing market for portable electronicdevices and the development of hybrid electric vehicles, there has been an everincreasing and urgent demand for environmentally friendly high-power energyresources. Supercapacitors is an efficient, clean and sustainable energy device, whichhave attracted significant attention. This is due to supercapacitors’high power density,long cycle life, rapid charging–discharging rates, which is better than traditionaldielectric capacitors and batteries/fuel cells.The electrode material is one of the most important factors that directly affect theperformance of supercapacitor. The metal hydroxide/oxides and conductive polymersis the constraint of capacitor electrode material, which is through the redox reaction toimprove high capacitance. However, their high cost and worse electrochemicalstability is one of the main factors to limit their commercialization. Compared withmetal oxide hydroxide electrode materials, carbon-based supercapacitor have a longercycle life. Because of electric double layer capacitor storage energy is pureelectrostatic attraction between ions and the charged surface of an electrode, which isa physical process, without structure changing and the redox reaction.The low capacity and energy density is the fatal flaws of EDL. Therefore, whenwe preparing supercapacitor should be on the premise of cost savings at the same timeimproving the capacitance. There are many kinds of ways to improve the capacitanceof electric double layer capacitors. Recently, many researchers reported the methodsto improve the capacitance of activated carbon with added redox-active material in theelectrolyte, which can set off redox reaction on the surface of the electrolyte andelectrode to contributing artifact capacitance.So the purpose of this paper is to choose the low cost activated carbon as electrode materials,then improving the capacitance byadding the oxidation reduction material. The main contents of this thesis aresummarized as follows:Firstly, EDLCs were also produced by using commercial ACs for electrodematerials,and the electrochemical performance of ACs has been investigated. Theresults show that the activated carbon electrodes have good electric double layercapacitance. The quality of active material and the ratio of active carbon, conductivegraphite and binder have a certain influence on the specific capacitance.To increase the potential window and specific capacitance at the same time, theperformance of carbon fiber paper/activated carbon electrode in different electrolytehave been studied.The carbon fiber paper/activated carbon electrode in0.1MKOH+3MKCl solutioncan achieve a higher potential window (-1V~0.4V) and specific capacitance (230F/g).The mixed solution of0.1MKOH+3MKCl were respectively added0.1MK3Fe(CN)6,0.1MK4Fe(CN)6and0.05MPPD, the CV curves of carbon fiber paper/activatedcarbon electrode have an obvious redox peak, and the specific capacitance increasesobviously, which is respectively355F/g,224F/g and353F/g.Finally,four types of supercapacitor with different electrolyte was assembled.Thespecific capacitance of AC/KOH-AC/KOH supercapacitor is37F/g when currentdensity of1A/g.And the energy density could reach5.1Wh/kg at a power density of496w/kg; AC/KOH+KCl-AC/KOH+KCl supercapacitor can get wide potentialwindow (0V~1.4V) with the specific capacitance of40F/g, and the energy densitycould reach10.9Wh/kg at a power density of719W/kg; AC/KOH+K3Fe(CN)6–AC/KOH+K4Fe(CN)6contribute to the pseudocapacitance, specific capacitance boostwith the increase of potassium ferricyanide and potassium ferrocyanide, the highestspecific capacitance is91.7F/g when n=0.4M, the energy density could reach18.34Wh/kg at a power density of600W/kg; AC/KOH+KCl+K3Fe(CN)6–AC/KOH+KCl+PPD supercapacitor can get wide potential window (0V~1.5V) andhigh specific capacitance of100F/g, the energy density could reach31.3Wh/kg at apower density of750W/kg. |
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