Metal Oxide Supercapacitor

In recent ten years, the new power technology has been accelerated to meet the requirement of portable electrical appliance and electric vehicle. The supercapacitor is a kind of green energy storage device characterized by high power and long-life. It is a practical answer to the world's pressing need for clean and efficient power due to its advantages. Supercapacitors are divided into three categories; electric double layer supercapacitor, Faraday pseudocapacitance supercapacitor, and hybrid supercapacitor respectively. The Faraday pseudocapacitance, due to the metal oxide electrodes/solution in the interface reaction, is much more than carbon double-layer capacitance. Thus it attracted many researchers interest. My work focused on some different transition metal oxides and studied their Faraday pseudocapacitance performance.However, the energy density of supercapacitors is still much less than that of recharge batteries. The lower energy density restricts the development of supercapacitors. Thus, many researches on the supercapacitors aim to increase energy density of supercapacitors. According to the equation E=1/2 CV2, two effective approaches can be used to improve the energy density of supercapacitors. One is to develop hybrid system with higher work voltage (V); the other is increasing the capacitance(C). The capacitance is influenced by two factors-the electrode material and the electrolyte. My work mainly focused on the study about increasing the capacitance through change the electrode material and the electrolyte:1. Electrochemical capacitance performance of ordered mesoporous Co3O4 synthesized by template method:The Faraday pseudocapacitance is produced by the redox reaction on the surface of electrode. Based on this principle, nanoporous electrode materials will increase the capacitance. The contact surface between the electrode material and electrolyte will be enlarged obviously due to nanoporous structure, in order to increase the utilization and the capacitance of the materials. At the same time, this kind of structure is good for the transfer of the electrolyte ions.In this part, ordered crystallized Co3O4 nanoarrays were synthesized by replicating mesoporous silica template and its electrochemical capacitance performance was evaluated in 6 mol/L KOH electrolyte solution. The ordered structure has a pore size distribution of 3-4nm and a large surface area of 83m2/g. The electrochemical tests results indicated that the ordered mesoporous structure of Co3O4 nanoarrays provide a higher capacitance of 250 F/g and exhibit a good rate capability. This is due to that the well ordered mesoporous structure provides large specific surface area and facilitates the fast transport of the electrolyte.2. Electrochemical capacitance performance of nanostructure MnO2 by precipitation method:MnO2 has been taken more attention and attraction in terms of cheaper, more abundant, and more environmentally friendly than noble metal oxides and other transition metal oxide systems as supercapacitor material. A significant approach for increasing specific capacitance of MnO2 is decreasing the particle size during the research work.In my work, a simple precipitation method was used to synthesize the MnO2 material. The amorphous MnO2 with a nanosheet structure was prepared by the reaction of KMnO4 and aniline in different concentration SDS solution. The electrochemical test was evaluated in 1 M Li2SO4 electrolyte solution. Through the experiment, the pre-MnO2 had a largest capacitance of 237 F/g when the concentration of SDS is 0.2 M. Further, the calcination experiment was carried out by different calcinated condition. The Li+ insertion reaction is observed in the calcined-MnO2. Two pairs of redox peak were observed between 0.7V to 1V. It indicated that the spinel LiMnO4 was produced by the electrochemical process. The obtained calcined-MnO2 electrode could exhibit a good capacitance of 229F/g and a wider working potential window than pre-MnO2.3. Effect of the pore size on the charge/discharge efficiency for the pseudo-capacitive NiO in the mixed electrolyte of KOH and hexacyanoferrate:A major breakthrough in electrochemical capacitor electrodes is the development of various alternatives as a replacement for RuO2. As these cheap transition metal oxides usually exhibit lower electrochemical capacitance performance, many researches have been carried on developing these metal oxides with various morphologies to increase their surface area, while very few works have investigated the electrolytes used in capacitors except selecting aqueous solutions. In this research, our interest is the active addition of the electrolyte.Five kinds of NiO materials with different pore size distribution were synthesized and their electrochemical capacitance characterizations were studied in 3 M KOH electrolyte solution with the hexacyanoferrate as the addition. The capacitance is improved because of the reaction of the hexacyanoferrate. But the hexacyanoferrate diffusion will induce self-discharge. We synthesized five kinds of NiO materials with different surface areas and. And the electrochemical test results indicated the pore size distribution of the material impacts the self-discharge. Through the experiment, the optimum pore size distribution is about 15 nm. The material with this pore size distribution would shackle hexacyanoferrate ion effectively due to decrease the fading of the capacitance which the diffusion induced. Consequently, the capacitive performance was improved during the optimization.