【作者】 李焕新；

【导师】 周海晖； 冯斌；

【作者基本信息】 湖南大学 ， 化学工程（专业学位）， 2016， 硕士

【摘要】 超级电容器是一种重要的储能装置,其电极材料的电化学性能很大程度上决定了超级电容器的容量。而生物质是重要的可再生能源之一,利用可再生能源取代部分化石能源可以一定程度上缓解环境恶化和气候变暖。我国现阶段对生物质的利用率还不是很高,很多生物质如：秸秆、玉米杆和玉米芯都被焚烧或废弃,造成资源的浪费和环境的污染。尽管不同生物质的成分有所差异,但其基本元素大同小异,例如植物生物质主要含有纤维素、半纤维素、木质素、植物蛋白和植物脂肪等成分,基本都由碳、氢、氧、氮、硫这几种元素构成,且碳元素占主要成分。因此,利用生物质制备高性价比的活性碳材料应用于超级电容器电极材料既可提高可再生能源的利用率,又有望于解决储能技术的关键问题。本论文采用废弃的生物质去粒玉米芯,制备了高比容量且性能稳定的超级电容器电极材料,该材料在大功率超级电容器储能装置方面具有良好的应用前景。经表征,该材料是一种具有三维多孔结构,且均匀负载过渡金属氧化物纳米颗粒的氮掺杂碳纳米复合材料,其中孔网结构的碳纳米材料提供了巨大的比表面积和良好的导电性,而掺杂的氮原子很好地改善了材料的电荷分布并提高电子转移速率,同时过渡金属氧化物的赝电容可进一步提高材料的电容值。论文取得了以下几个方面的研究结果：(1)利用一步煅烧法直接制备了玉米芯活性碳纳米材料。通过对升温程序的调控,确定了最佳升温速率、煅烧温度和保温时间。对最优条件下制备的样品进行氮气吸脱附和孔径分布测试,结果表明其Brunauer-Emmett-Teller (BET)比表面积高达1055 m2 g-1,且孔径均匀分布在4-5 nm。同时利用扫描电子显微镜(SEM)和X-射线衍射(XRD)表征其形貌和组成成分,发现该纳米材料为三维多孔结构并均匀负载着Fe203纳米粒子。在6 M KOH溶液中,利用电化学工作站通过循环伏安法和恒电流充放电法测试其电化学电容性能,在1 A g-1的电流密度下其电容值达345 F g-1。(2)利用三聚氰胺作为氮源前驱体,将玉米芯粉末与其充分混合再一起煅烧,制备了掺氮功能化碳纳米材料。经对煅烧温度、煅烧时间和三聚氰胺比例调控,确定了最优条件。对最优条件下制备的样品进行氮气吸脱附和孔径分布测试,结果表明其BET比表面积达到了1100 m2 g-1,孔径分布在40-50 nm之间。利用XRD、X射线光电子光谱分析法(XPS)、SEM、超高分辨透射电子显微镜(HRTEM)和mapping表征其形貌及组成,结果表明掺氮后的碳纳米材料在孔网结构的介孔碳表面生长了许多的薄壁碳纳米管,且纳米管的端口附着球形颗粒。其主要成分为C、N、O和Fe,还有微量的S元素。纳米管形成区域由氮和氧两种元素组成,端口处球形颗粒为Fe2O3纳米粒子。同样在6 MKOH溶液中测试了其电化学性能,结果表明其电容值高达579 F g-1。更多还原

【Abstract】 Supercapacitor is an important energy storage device and its electrochemical properties of the electrode material basically determine its capacity. Besides, biomass is one of the most important renewable energies and rationally using it to replace the fossil energy could alleviate environmental degradation and global warming to some extent. However, in our country, the utilization rate of biomass is not high at present. Many biomass, such as straws, corn stalks and corn cobs, were burned or abandoned, causing resources waste and environment pollution. Although the compositions of various biomass are different, their basic elements are similar. For example, plant biomass mainly contains cellulose, hemicellulose, lignin, plant protein, plant lipid and so on, and substantially consists of carbon, hydrogen, oxygen, nitrogen, sulfur, especially carbon occupying the main element. Therefore, utilizing biomass to prepare cost-effective carbon materials for the electrode of supercapacitor not only improves the utilization rate of renewable energy but also provides a promising way to solve the key problems of energy storage technology. In this essay, corn cobs were selected to synthesize supercapacitor electrode material with high capacitance and stable performance, which is a promising material for high-power supercapacitor energy storage device. The characterization results show that this nitrogen doping carbon nanocomposite owns a three-dimensional pore-network structure, loaded with transition metal nanoparticles. The pore-network structure of the carbon nanomaterial provides high specific surface and good electrical conductivity, and the doped nitrogen atom greatly improves the charge distribution and electron transfer. Meanwhile, transition metal oxide possesses a certain pseudocapacitance to enhance the capacitive property of the material. The results obtained are as follows:(1) The corncobs activated carbon nanomaterial was prepared by one-step calcining method. The optimal heating rate, annealing temperature and holding time were determined by regulating the temperature program. The optimized sample was measured with nitrogen adsorption-desorption test to characterize its specific surface area and pore size distribution, and the results show that its specific surface area reaches as high as 1055 m2 g-1 while the pore size distribution uniformly concentrates at 4-5 nm. Moreover, scanning electron microscopy (SEM) and X-ray diffractometer (XRD) were used to characterize its morphology and composition, finding that the material possesses a three-dimensional pore-network structure and is uniformly loaded with Fe2O3 nanoparticles. Electrochemical capacitance performance was tested in 6 M KOH solution using electrochemical workstation with cyclic voltammetry and chronopotentiometry, and the result demonstrates that the capacitance is 345 F g-1 at a current density of 1A g-1.(2) Melamine served as a nitrogen precursor, was mixed with corncobs powder and then calcined together to prepare nitrogen-doped functional carbon nanomaterial. The calcining temperature, calcining time and melamine ratio were adjusted to determine the optimμm condition. The sample prepared under the optimized condition was characterized by a BET test, and the results show that the specific surface area is up to 1100 m2 g-1 while the pore size distributes between 40-50 nm. Further, XRD, X-ray photoelectron spectroscopy (XPS), SEM, high resolution transmission electron microscopy (HRTEM) and mapping were used to characterize its morphology and composition. The results display that the nitrogen-doped carbon nanomaterial shows a pore-network structure with plenty of thin-walled carbon nanotubes growing on the surface of mesoporous carbon and some spherical particles attaching on the port of nanotubes. This carbon nanomaterial is made up of four main elements (C, N, O and Fe) and few S element. The nanotubes consist of two elements (C and N) and the spherical particles on the port are Fe2O3 nanoparticles. The electrochemical performance was also tested in 6 M KOH solution, and the result shows that the capacitance value is up to 579 F g-1.更多还原