Department of Chemical and Biomolecular Engineering, Sogang University , Seoul, 121-742, Republic of Korea.
ACS Appl Mater Interfaces. 2014 Jan 8;6(1):706-11. doi: 10.1021/am404960r. Epub 2013 Dec 23.
We have provided a design of the macroscopic morphology of carbon nanotubes (CNTs) using emulsion droplet confinement. The evaporation of CNT-dispersed aqueous emulsion droplets in oil produces spherical CNT assemblies, i.e., CNT balls. In this emulsion-assisted method, compact packing of CNT was obtained by the presence of capillary pressure during droplet evaporation. The size of the CNT balls could be controlled by changing the concentration of the CNT dispersion solution; typically, CNT balls with an average size in the range of 8-12 μm were obtained with a Brunauer-Emmett-Teller (BET) specific area of 200 m(2)/g. Heat treatment of the CNT balls, which was required to remove residual solvent, and cement CNTs was followed, and their effect has been characterized; the heat treatment at high temperature desorbed surface oxygenated groups of CNTs and created defective carbon structures, but did not change pore structure. The dispersion of CNT balls was applied to form CNT ball-assembled film for a supercapacitor electrode. The specific capacitance of 80 F/g was obtained at 500 °C heat treatment, but the CNT balls prepared at a higher temperature actually decreased the capacitance, because of the removal of surface oxygenated groups, thereby decreasing the pseudo-capacitance. The capacitive properties of CNT ball-assembled electrodes were compared to CNT films; the CNT ball electrodes showed 40% higher specific electrochemical capacitance and higher rate performance, which is attributed to the compact packing of CNTs in the CNT ball and the hierarchical porous structures in the ball assemblies.
我们提供了一种使用乳液液滴限制来设计碳纳米管（CNT）宏观形态的方法。在油中蒸发 CNT 分散的水乳液液滴会产生球形 CNT 组装体，即 CNT 球。在这种乳液辅助方法中，由于液滴蒸发过程中存在毛细压力，因此可以获得 CNT 的紧密堆积。通过改变 CNT 分散溶液的浓度可以控制 CNT 球的尺寸；通常，可以获得平均尺寸在 8-12 μm 范围内的 CNT 球，BET 比表面积为 200 m(2)/g。随后对 CNT 球进行热处理以去除残留溶剂并胶凝 CNT，对其效果进行了表征；高温热处理会解吸 CNT 的表面含氧基团并产生缺陷碳结构，但不会改变孔结构。将 CNT 球的分散体应用于形成用于超级电容器电极的 CNT 球组装膜。在 500°C 热处理下获得了 80 F/g 的比电容，但是在较高温度下制备的 CNT 球实际上降低了电容，因为表面含氧基团的去除降低了赝电容。比较了 CNT 球组装电极的电容性能与 CNT 薄膜；由于 CNT 球中 CNT 的紧密堆积和球组装体中的分级多孔结构，CNT 球电极表现出 40%更高的比电化学电容和更高的倍率性能。
