【作者】 周应和；

【导师】 刘洪波；

【作者基本信息】 湖南大学 ， 材料学， 2006， 硕士

【摘要】 本文以中间相炭微球(Mesocarbon Microbeads,简称MCMB)为原料,以KOH为活化剂制备球形高比表面积活性炭(High Surface Area Activated Carbon,简称HSAAC)。系统考察了碱炭比、活化温度、保温时间与升温速率等工艺因素对活性炭微球的收率、粉末电阻率、碘吸附性能及孔结构的影响,确立了调控活性炭微球孔结构与性能的工艺方法和工艺条件。通过考察活化工艺条件对活性炭微球比表面积与孔结构的影响,同时结合XRD、SEM、DSC和能谱分析手段,探讨了MCMB的KOH活化机理与活化成孔过程。将所制备的活性炭微球通过适宜的工艺制成活性炭电极,组装成双电层电容器(Electric Double-layer Capacitor,简称EDLC),考察其在30wt%的KOH电解液中的直流充放电性能、循环伏安性能与交流阻抗性能,研究了活化工艺条件对EDLC比电容、等效串联电阻和频率响应特性的影响,以及比电容、频率响应特性与孔结构之间的关系。活化机理分析表明,MCMB的KOH活化过程中同时包含活化反应与炭化反应两个既相互独立又相互联系的过程。在炭化过程中芳族扁平分子不断缩聚长大,并向炭六角网格平面转化。与此同时,有序堆叠区域即所生成的石墨微晶尺寸也随着热处理温度的提高而增大。MCMB的KOH活化实质上是发生氧化-还原反应以主要生成K2CO3而消耗碳的过程,由于实验所用的MCMB具有独特的Brooks-Taylor结构,因此MCMB在KOH活化成孔过程中表现出明显的各向异性,孔隙更容易在平行层面方向上形成。研究表明,与固态混合法相比,采用溶液混合法制备的活性炭微球具有更高的比表面积、总孔容和碘吸附性能,从而具有更高的比电容,并且活化收率也有所提高。在MCMB的KOH化学活化过程中,碱炭比、活化温度、保温时间是影响活性炭微球结构和性能的主要工艺因素。随着碱炭比的增大,活化温度的升高,保温时间的延长,活性炭微球的收率逐渐减少,比表面积、总孔容、碘吸附值和比电容均呈先增大后减小的变化规律。升温速率和KOH溶液浓度对活性炭微球结构与性能的影响较小。通过正交试验优化出制备活性炭微球的最佳工艺条件为碱炭比5:1,活化温度850℃,保温时间1h。在该工艺条件下所制备的活性炭微球的比表面积达3337.2m2/g,总孔容达2.04cm3/g(中孔含量41.2%),碘吸附值为2705.2 mg/g。与石油焦和无烟煤等炭质原料相比,由MCMB制备的HSAAC具有很高的比表面积和总孔容,且孔径分布窄、中孔含量高、吸附性能优异,因此MCMB是制备HSAAC的理想原料,特别适合用作EDLC电极材料。按上述优化工艺制备的活性炭微球电极在30wt%的KOH电解液中的比电容高达88.3 F/g,以该活性炭微球作电极材料的EDLC具有较小的漏电流和内阻,优良的循环性能和频率响应特性,既可小电流长时间充放电,也可大电流短时快速充放电,完全能满足不同用途的需要。更多还原

【Abstract】 In this paper, the high specific surface area activated carbon (HSAAC) was prepared from mesocarbon microbeads (MCMB) by the activation of KOH. The influences of the weight ratio of KOH to MCMB, the velocity of pyrogenation, the activation temperature and activation time on yield, powder specific resistance, adsorption properties and pore structure of activated mesocarbon microbeads had been systematically investigated. Based on these, the technologic methods and conditions which the pore structure and properties of activated mesocarbon microbeads were established. After analyzing the effects of the activation conditions on BET specific surface area and pore structure, the activation mechanism of KOH and the process of pore formation were discussed by use of SEM, XRD, DSC and energy spectrum analysis. Activated mesocarbon microbeads were used as electrode materials of electric double-layer capacitor (EDLC), its performance in 30wt% KOH electrolyte was determined by DC charge-discharge, cyclic voltammetry and AC impedance. The effects of activation conditions on specific capacitance, equivalent series resistance(ESR) and frequency response properties were investigated. Furthermore, the relations between the pore structure and the properties mentioned above were discussed.The analysis of activation mechanism shows that, there are two aspects of reaction such as activation and carbonization resisting in course of activation of MCMB by KOH. During carbonization, the polymerized flat aromatic molecules of microbeads grow and synchronously transform into hexangular-plane carbon layer. Meanwhile, the activation is an oxidation-reduction reaction which turns C into K2CO3. Due to the unique“globe-like”(Brooks-Taylor) structure, anisotropy is obviously observed in activation process. It means that pores are much easier to form and develop in the parallel direction of carbon layer compared with the vertical direction.Experiment results show that, compared to being mixed with KOH solid powder, the BET specific surface area, total pore volume and value of iodine absorption were enhanced when MCMB was mixed with KOH solution before activation. Moreover, the specific capacitance and yield of activated mesocarbon microbeads were also increased. The KOH/MCMB weight ratio, activation temperature and activation time are the main factors which influence the structure and performance of activated mesocarbon microbeads. When KOH/MCMB weight ratio, activation temperature and activating time increased, the BET specific surface area, total pore volume and value of iodine absorption increase firstly and then decrease. However, the yield of activated mesocarbon microbeads decreases gradually with the increasing of these factors. However, the velocity of pyrogenation and concentration of solution have a little influence on structure and performance.The optimum process conditions of preparing activated mesocarbon microbeads are KOH/MCMB ratio of 5, activation temperature at 850℃and activation time for 1 hours. When at the optimum process conditions mentioned above, the activated mesocarbon microbeads’BET specific surface area reaches 3337.2m~2/g, and its total pore volume and iodine absorption value are 2.04cm~3/g, 2705.2 mg/g respectively. The value of BET specific surface area, total pore volume and iodine absorption are much higher than those of HSAAC based on anthracite or petroleum coke. Moreover, activated mesocarbon microbeads have high mesopore content (41.2%) which is benefit for using as electrode materials of EDLC. Using activated mesocarbon microbeads as electrode materials, the specific capacitance of electrode in 30wt% KOH electrolyte reaches 88.3 F/g. This EDLC has good cycle performances and excellent properties of frequency response. It can charge-discharge not only under the small current and long time, but also under the large current and short time. In addition, its internal resistance and drain current are very small, so can suit with different practical application.更多还原