多孔碳纳米球的制备及其电化学性能

摘要

以三嵌段共聚物F108为软模板,通过水热法合成酚醛树脂球并在氮气氛围下碳化、KOH活化处理,最终得到多孔碳纳米球材料.通过扫描电子显微镜、透射电子显微镜和氮气吸附分析仪对样品进行表征,结果表明样品的平均粒径为120 nm,球形度高,比表面积达到1403 m2/g,孔径分布广.通过X射线衍射研究样品的结晶度,傅里叶红外光谱分析样品表面官能团的情况,结果表明KOH处理和高温处理使得样品的微晶结构有序度提高,表面官能团含量降低.以多孔碳纳米球作为超级电容器电极的活性物质,电化学特性测试结果表明,多孔碳纳米球材料的比电容能够达到132 F/g(0.2 A/g),在10 A/g的电流密度下,经过10000次循环充放电后,电容量保留率为97.5%.本文采用水热法制备的多孔碳纳米球电化学性能良好,适用于超级电容器电极材料,研究结果表明,比表面积大、孔径分布合适(具有一定介孔含量)、结晶度高和含有少量表面官能团的理化特性的电极材料,其电化学性能更加优越.%Nanostructured carbon materials possessing good mechanical properties, adsorption characteristics and electro-chemical performances, are the most promising candidate for electrode materials of supercapacitors. Among all syn-thesis methods, hydrothermal synthesis of porous carbon nanosphere (PCNS) is mostly used. Structure-directing agent F108 (PEO132-PPO50-PEO132) has a similar function to popular agent F127(PEO106-PPO70-PEO106) and P123 (PEO20-PPO70-PEO20) used in hydrothermal synthesis, but has greater relative molecular mass and higher hydrophilic/hydrophobic volume ratio, so using block copolymer F108 as soft template will obtain PCNS with special physicochemical properties. In this paper, PCNS is prepared by post-processing, including carbonization and subsequent KOH activation, of phenolic resin nanoparticles obtained by hydrothermal synthesis through using phenolic resin as a carbon source and block copolymer F108 as a soft template. The as-prepared PCNS sample is characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction, nitrogen adsorption and FTIR, etc. The images of SEM, TEM and results of nitrogen adsorption show that the obtained PCNS has the advantages, such as uniform particle size about 120 nm, high spherical degree and large specific surface area of 1403 m2/g and also wide pore size distribution. The results show that post-processing has an important influence on the physicochemical property of PCNS sample such as specific surface area, pore size distribution, crystallinity and surface chemistry. The activation temperature plays an important role in forming pore structure as the specific area of PCNS sample increases from 519 m2·g?1 to 1008 m2·g?1 after activation at 700 ?C (PCNS700), while the activation temperature changes to 900 ?C (PCNS900), the specific area rises up to 1403 m2·g?1. The pore size distributions show that the peaks are at the same position, which suggests that KOH activation at high temperature makes the primary pore of PCNS deeper. PCNS900 contains more mesopores than PCNS700, so it can be concluded that at the higher activation temperature, the deeper pores inside PCNS are formed, and it is worth noting that pores near 2 nm are largely produced when the temperature arrives at 900 ?C. KOH processing and high temperature processing contribute greatly to structural ordering, which means that PCNS samples are greatly graphitized. Last but not least, both KOH processing and high temperature processing reduce the number of functional groups on the surface of PCNS samples. Using PCNS samples as activated material to make electrodes, we study how the different physicochemical properties of PCNS samples affect the performance of PCNS electrode. As a result, PCNS700 and PCNS900 show notably larger specific capacitance than PCNS due to their great larger surface specific areas and more structural orderings in graphitic layer stacking. However, PCNS700 shows a lager specific ca-pacitance of 146.75 F/g than PCNS900 (132 F/g) due to its higher number of surface functional groups than PCNS900, though its lower specific surface area. The pore size distribution has a huge influence on the supercapacitor rate capa-bility as the PCNS900 which has more mesopores and the most structural orderings in graphitic layer stacking shows excellent rate capability as well as superior long-term cycling stability (97.5% capacitance retention over 10000 cycles). In summary, PCNS obtained by hydrothermal synthesis through using block copolymer F108 as soft template shows the special physicochemical properties which make it an ideal candidate for the electrode materials of supercapacitor. Moreover, the larger the specific area, more structural orderings in graphitic layer stacking, more appropriate content of mesopores and surface functional groups, the superior performance the electrode materials of surpercapacitor exhibit.