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碳包覆纳米金属氧化物的制备及其电容性能研究
Preparation and Capacitance Performance of Carbon-Encapsulated Metal Oxides as Electrode for Supercapacitor
【作者】 宋佳；
【导师】 宋怀河；
【作者基本信息】 北京化工大学 ， 材料科学与工程， 2011， 硕士
【摘要】 随着能源消耗的日益扩大,和全球变暖等环境问题的出现,人们对温室气体排放可控的新型的清洁能源以及更先进的储能器件的需求越来越紧迫。超级电容器作为一种新型的绿色、环保的储能器件应运而生,它集高能量密度、高功率密度、长使用寿命等特性于一身,具有十分广泛的应用领域。在超级电容器的研究中,高功率性能、高比容量的电极材料的开发具有重要的现实意义和理论价值。碳包覆纳米金属氧化物作为一种金属氧化物与碳复合的新型电极材料,兼具了碳材料的高功率性能以及金属氧化物的高比容量等优点,使其成为超级电容器电极材料的最佳选择之一。本文以碳包覆纳米金属颗粒(Carbon-encapsulated metal nanoparticles, CEMNP)为前躯体,采用直接氧化法和水热氧化法这两种方法来制备碳包覆纳米金属氧化物颗粒,研究了碳包覆纳米金属氧化物颗粒作为超级电容器的电极材料的电化学性能。分别用扫描电子显微镜、透射电子显微镜、高分辨透射电子显微镜、X射线衍射、傅里叶红外光谱对产物的外部形貌和内部结构进行研究,并在质量浓度为30%的KOH的电解液中,利用循环充放电、循环伏安和交流阻抗手段测试了作为超级电容器电极材料的电化学性能。研究表明,采用直接氧化法在300℃温渡下制备的碳包覆纳米氧化镍颗粒(NiO@C)的粒径在10～20 nm。根据氧化时间的不同,氧化10小时的反应产物呈现最高的电化学性能,在0.1 A/g的电流密度下,比容量可以达到193 F/g,且有较好的功率性能。直接氧化法在270℃高温下制备的碳包覆纳米氧化钴颗粒(Co3O4@C),粒径在30-40 nm,同时有一定量的空心结构Co3O4@C颗粒产生(Co3O4@C-HNPs)。其中氧化时间为24 h的样品电化学性能最佳,在0.1 A/g的电流密度下,比容量可以达到108F/g,且有较好的功率性能。水热氧化法是本文探索的制备碳包覆纳米金属氧化物颗粒的新方法,即以碳包覆纳米金属颗粒为前躯体,以30%的H202作为氧化剂,在高压水热釜中,200℃下反应不同时间。这种方法制得的碳包覆纳米金属氧化镍颗粒中,出现了一定量的空心结构。其中,氧化15小时的样品的电化学性能最好,其比容量在0.1 A/g的电流密度下高达966 F/g,即使在大电流密度2 A/g下也仍有402 F/g,表现出极好的电容性能。该结果表明：水热法制备的碳包覆纳米金属氧化镍的电化学性能远远优于直接氧化法制得的样品。究其原因,是由于该法生成的大量的空心结构为氧化镍的氧化还原反应提供了更多的反应活性点,同时碳包覆层表面被氧化形成的官能团也对赝电容做出了贡献。
【Abstract】 The ever worsening energy depletion and global warming issues call for not only urgent development of clean alternative energies and emission control of global warming gases, but also more advanced energy storage and management devices. As a green and friendly new energy storage device, supercapacitors emerge as the times require. Supercapacitors have been applied in many fields because they possess high power density, high energy density, long cycle-life, and so on. In the research of supercapacitors, the development of electrode materials, with high-rate performance and high specific capacity, has significant realistic meaning and theoretical value. Carbon-encapsulated metal oxides is a new kind of composite electrode material, which posses the high power density of carbon and the high energy density of metal oxide. As a result, they will become one of the optimal choice of electrode material in supercapacitors. In this thesis, carbon-encapsulated metal oxides nanoparticles(CEMONP) were synthesized by carbon-encapsulated metal nanoparticles(CEMNP) via direct oxidation or hydrothermal oxidation methods and were applied as the electrode materials for supercapacitor. The morphologies and structures of CEMONP were characterized by Scanning Electron Microscope(SEM), Transmission Electron Microscope(TEM), high resolution TEM(HRTEM), X-ray Diffraction (XRD), Fourier transform Infrared spectroscopy (FTIR). Electrochemical performances were investigated by constant current Galvanostatic charge/discharge test, cyclic voltammetry and alternating current impedance in 30wt.% KOH electrolyte.The results show that the particle size of carbon-encapsulated nickel oxide nanoparticles(NiO@C) synthesized from direct oxidation at 300℃is 10～20 nm. According to the different time of oxidation, the product oxidized at 300℃for 10 hours showed the best electrochemical performance with a high specific capacitance of 193 F/g under the current density of 0.1 A/g and good power performance. Besides, carbon-encapsulated cobalt oxide nanoparticles synthesized by this method at 270℃possessed uniform particle size of 30～40nm and hollow structure (Co3O4@C-HNPs), and the sample oxidized 24 hours at 270℃showed the best electrochemical performance, which exhibited the specific capacitance of 108 F/g under the current density of 0.1 A/g.In this thesis, we also founded a new approach called hydrothermal oxidation method to synthesize CEMONP, in which CEMNP was used as the starting material,30% H2O2 as the oxidant and oxidation took place in a Teflon-lined autoclave at the tempreture of 200℃for different time. By this way, carbon-encapsulated NiO hollow nanoparticles were obtained and the product oxidized 15 hours showed the specific capacitance as high as 966 F/g under the current density of 0.1 A/g and still keeping 402 F/g even under the higher current density of 2 A/g. Obviously, the electrochemical performance of NiO@C synthesized by this method was better than the former method. The reasons should be attributed to the hollow structure which provide more active sites for the redox reaction of nickel oxide. At the same time, the functional groups formed at the surface of carbon shell improved the pseudocapacitance.