碳化物衍生碳的形成机理及其超级电容性能研究

发布时间：2018-08-22 19:23

【摘要】：碳化物衍生碳(Carbide-derived carbon,简称CDC),是以碳化物晶格为模板,通过逐层去除其中的非碳原子而获得的一类新型纳米骨架碳。CDC除了拥有高比表面和发达的孔隙外,还具有其它碳材料所没有的特性,例如孔径大小及分布精确可调,形貌丰富等。这些特性使CDC在很多领域拥有巨大的应用潜力,如氢储、超级电容器电极材料、催化剂载体、自润滑涂层等。本论文针对目前关于CDC形成机制认识的不足,以碳化物/CDC转变界面为研究对象,分析揭示了CDC中各微结构的形成机制;研究了在碱性电解液中不同结构CDC作为超级电容器电极材料时的电容性能,探索了通过改善CDC的润湿性以提高其在碱性KOH电解液中超级电容性能的思路与途径;系统研究了在碳化物前驱体中球磨引入铁催化剂对CDC微结构及超级电容性能的影响。主要的研究工作和结果如下:(1)分别采用VC,TiC和NbC作为前驱体,通过短时(10分钟)氯化蚀刻获得相应的碳化物/CDC界面结构,借助HRTEM等对其微观结构特征进行表征,探索分析了CDC的形成机制,并且研究比较了具有不同结构特征的的CDC在碱性电解液中的电容特性。结果表明:CDC属于共形转变,碳化物向CDC的转变时刻伴随应力的存在,这是导致CDC中微结构不同的重要原因;对于具有相同结构的碳化物前驱体,单位体积碳化物中的碳原子浓度越低,转变界面处产生的应力越大,相同条件下形成的CDC结构越无序;CDC中的孔是由于界面附近石墨层间应力积聚过大造成层间撕裂形成的,它可被看成是前驱体空间被蚀刻后生成的石墨层分割所形成,CDC中的石墨层越厚,孔尺寸越大,相应的比表面越低;具有低碳原子体积浓度的NbC,转变界面处的巨大应力致使所得CDC主要为1~2层的卷曲石墨烯,具有2200m~2g~(-1)的高比表面微孔结构使NbC-CDC作为电极材料时具有更高的比电容值,其值高达147Fg~(-1)。(2)以不同有序度的CDC为对象,研究了它们在KOH水系电解液中的润湿情况以及对超级电容性能的影响。为解决石墨化CDC润湿性差,在水系电解液中超级电容性能不佳的问题,探索了KOH电解液中添加乙醇以及CDC硝酸活化改性等措施对石墨化CDC的润湿性及超级电容性能的影响。结果表明:CDC在碱性电解液中的润湿性随石墨化程度的增加而降低,这使材料的电容性能受到了严重影响;通过在KOH电解液中添加乙醇可有效地改善石墨化碳在KOH电解液中的润湿性,并使材料的电容性能得到极大改善,且当乙醇添加量为10wt.%时电容性能达到最优,其比容由6Fg~(-1)增加到65Fg~(-1)。硝酸活化改性可在CDC结构内部引入含氧官能团,使石墨化CDC在碱性电解液中的润湿性得到极大改善,从而有效提升材料的超级电容特性,进行高浓度活化后,其比容值可由原来的6Fg~(-1)增加到近130Fg~(-1)。(3)分别以VC,TiC和SiC为前驱体,蚀刻前利用球磨在碳化物前驱体中引入催化剂,系统研究了铁催化剂的引入对所得CDC的微结构以及超级电容性能的影响。结果表明:球磨引入催化剂过程中,碳化物前驱体不断被破碎焊合,部分铁催化剂被包埋在颗粒内部,确保在氯化蚀刻过程中起有效催化作用;破碎造成的缝隙因共形转变而以中孔的形式保留在蚀刻所得的CDC中;在低温蚀刻时,铁催化剂使TiC和VC蚀刻所得CDCs的石墨化度得到了极大提升,但当温度提升到一定值时,石墨化度发生了急剧降低,微孔得到了极大提升,伴随球磨引入的中孔使所得的CDC表现出了优异的超级电容性能;在SiC中球磨引入铁催化剂致使所得CDC中形成了大量具有较大晶面间距的中空碳纳米洋葱。
[Abstract]:Carbide-derived carbon (CDC) is a new type of nano-skeleton carbon, which is obtained by removing non-carbon atoms from the lattice of carbide layer by layer. In addition to having high specific surface area and developed pores, CDC also has the characteristics that other carbon materials do not have, such as pore size and distribution of accurate adjustable, shape. These characteristics make CDC have great potential applications in many fields, such as hydrogen storage, electrode materials for supercapacitors, catalyst supports, self-lubricating coatings and so on. The capacitive properties of CDCs with different structures in alkaline electrolyte as electrode materials for supercapacitors were studied, and the way to improve the Supercapacitive properties of CDCs in alkaline KOH electrolyte by improving their wettability was explored. The main research work and results are as follows: (1) Using VC, TiC and NbC as precursors, the interfacial structure of carbide/CDC was obtained by chlorination etching in a short time (10 minutes). The microstructure characteristics were characterized by HRTEM, and the formation mechanism of CDC was explored and compared. The results show that CDC belongs to conformal transition and the stress exists when the carbide changes to CDC, which is an important reason for the different microstructure of CDC. For the precursors with the same structure, the lower the concentration of carbon atoms per unit volume of carbide, the production of transition interface occurs. The larger the stress generated, the more disordered the structure of CDC formed under the same conditions; the holes in CDC are formed by the tearing of the graphite layer caused by the excessive stress accumulation near the interface, which can be seen as the separation of the graphite layer formed by etching the precursor space. The thicker the graphite layer in CDC, the larger the pore size, and the lower the specific surface. The high specific capacitance of NbC-CDC as electrode material is higher than that of NbC-CDC with low carbon atom volume concentration and the tremendous stress at the transition interface, which results in the formation of 1-2 layers of convoluted graphene. The high specific surface microporous structure of 2 200 m-2 g-1 makes the specific capacitance of NbC-CDC as electrode material as high as 147 Fg-1. In order to solve the problem of poor wettability of graphitized CDC and poor performance of supercapacitor in KOH aqueous electrolyte, the effects of adding ethanol to KOH aqueous electrolyte and activation modification of CDC with nitric acid on the wettability and supercapacitor performance of graphitized CDC were investigated. The results show that the wettability of CDC in alkaline electrolyte decreases with the increase of graphitization degree, which seriously affects the capacitive properties of the material. Adding ethanol to KOH electrolyte can effectively improve the wettability of graphitized carbon in KOH electrolyte, and greatly improve the capacitive properties of the material, and when the ethanol content is 10 W. The specific capacitance of graphitized CDC increases from 6Fg~(-1) to 65Fg~(-1). Nitric acid activation can introduce oxygen-containing functional groups into the structure of CDC, which greatly improves the wettability of graphitized CDC in alkaline electrolyte, thus effectively improving the Supercapacitive properties of the material. After high concentration activation, the specific capacitance can be increased from 6Fg to 65Fg~(-1). (-1) was increased to nearly 130Fg (-1). (3) With VC, TiC and SiC as precursors, catalysts were introduced into carbide precursors by ball milling before etching. The effects of iron catalyst on the microstructure and supercapacitance properties of the obtained CDCs were studied systematically. In soldering, some iron catalysts are embedded in the particles to ensure effective catalytic action during chlorination etching; cracks due to conformal transformation remain in the form of mesoporous etched CDC; at low temperature etching, iron catalysts make TiC and VC etched CDCs graphitization degree has been greatly improved, but when the temperature is high. When the graphitization degree was raised to a certain value, the graphitization degree decreased sharply, and the micropores were greatly enhanced. The resulting CDC exhibited excellent Supercapacitive performance accompanied by the introduction of the mesopores by ball milling.
【学位授予单位】：燕山大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ127.12;TM53

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