Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
ACS Nano. 2010 Apr 27;4(4):2345-55. doi: 10.1021/nn901916m.
Supercapacitors composed of carbon nanotube (CNT) micropores in the room-temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI+BF4(-)) are studied via molecular dynamics (MD)computer simulations. It is found that the distribution of RTIL ions inside the micropore varies significantly with the pore size. Internal solvation of small (6,6) and (7,7) CNTs with an electrified interior wall is effected almost exclusively via counterions. Surprisingly, these counterions, even though they all have the same charge, lead to a charge density characterized by multiple layers with alternating signs. This intriguing feature is attributed to the extended nature of RTIL ion charge distributions, which result in charge separation through preferential orientation inside the electrified nanotubes. In the case of larger (10,10) and (15,15) CNTs, counterions and coions develop multilayer solvation structures. The specific capacitance normalized to the pore surface area is found to increase as the CNT diameter decreases from (15,15) to (7,7). As the pore size further reduces from (6,6) to(5,5), however, the specific capacitance diminishes rapidly. These findings are in excellent agreement with recent experiments with carbon-based materials. A theoretical model based on multiple charge layers is proposed to understand both the MD and experimental results.
通过分子动力学（MD）计算机模拟研究了在室温离子液体（RTIL）1-乙基-3-甲基咪唑四氟硼酸盐（EMI+BF4(-)）中的碳纳米管（CNT）微孔组成的超级电容器。研究发现，RTIL 离子在微孔内的分布随孔径大小有显著变化。带电荷内壁的小（6,6）和（7,7）CNT 的内部溶剂化几乎完全通过抗衡离子实现。令人惊讶的是，尽管这些抗衡离子具有相同的电荷，但它们导致电荷密度呈现出具有交替符号的多层结构。这种有趣的特征归因于 RTIL 离子电荷分布的扩展性质，这导致通过在带电纳米管内的优先取向发生电荷分离。在较大的（10,10）和（15,15）CNT 中，抗衡离子和共离子形成多层溶剂化结构。发现比电容与孔表面积的归一化值随 CNT 直径从（15,15）减小到（7,7）而增加。然而，当孔径进一步从（6,6）减小到（5,5）时，比电容迅速减小。这些发现与最近基于碳基材料的实验结果非常吻合。提出了一种基于多层电荷的理论模型来理解 MD 和实验结果。
