Electrochemical Double Layers in Confined Geometries

在这个项目中，我们想为在原子水平上描述纳米结构中的电解质奠定基础。在第一部分中，我们用密度泛函理论（DFT）研究了金纳米管和碳纳米管中的单离子和离子对。碱离子和卤化物离子被放置在狭窄的管中会自发电离，转移的电荷在管壁上形成像电荷。我们通过有效像半径的概念来表征管中的静电相互作用，这样我们就可以将我们的结果转移到纳米管中的离子集合中，我们通过统计力学和大规范蒙特卡罗模拟来检验。在第一阶段，我们发表了六篇文章，其中一篇是特邀章节。也许最引人注目的结果是半导体碳纳米管内外两个锂离子之间的明显吸引力，这可以解释在锂电池中观察到的类似吸引力。对这种效应的解释，我们有一个可行的假设，将是第二阶段的中心之一。此外，我们将按照我们原来的工作计划和进展到更大和更复杂的系统。因此，我们将从一维系统过渡到二维系统，然后再过渡到有限宽度的狭缝，以便研究几何形状对受限电解质的影响。此外，我们将研究溶剂化对纳米管和狭缝中离子的影响，包括这些结构中的输运。另一个主题是碳管掺杂对其屏蔽外场能力的影响，这影响了容量。我们的总体目标是从DFT中获得纳米系统的基本性质和各种粒子之间的相互作用，并用它们来描述大规范形式的粒子系综，其中界面电荷和电极电位的变化都是很好的定义。我们已经同意与两个实验组合作：Kaiser， Ulm教授，他用高分辨率透射电子显微镜研究碳结构，Unwin， Warwick教授，他可以用超高分辨率研究电化学过程。我们主要对这些受限系统的基本性质感兴趣：粒子和静电势的分布；它们储存电荷的能力；它们与整体溶液的平衡。我们研究的系统可用于超级电容器和锂离子电池。

In this project we want to lay the fundamentals for a description of electrolytes in nanoconfined structures at an atomic level. During the first part we have investigated single ions and ion pairs in gold and carbon nanotubes by density functional theory (DFT). Alkali and halide ions placed in narrow tubes ionized spontaneously, the transferred charge forming an image charge on the walls of the tube. We characterized the electrostatic interactions in the tube by the concept of an effective image radius, so that we could transfer our results to ensembles of ions in nanotubes, which we examined by statistical mechanics and by grand-canonical Monte Carlo simulations. In the first period we published six articles, one of them an invited chapter. Perhaps the most spectacular result is an apparent attraction between two Li-ions inside and outside a semiconducting carbon nanotube, which may explain a similar attraction observed in Li-batteries. The elucidation of this effect, for which we have a working hypothesis, will be one of the centers of the second period. In additions we shall follow our original work plan and progress to larger and more complicated systems. Thus we will pass from one-dimensional to two-dimensional systems and then to slits with a finite width, in order to study the effect of the geometry on the confined electrolytes. In addition we shall study the influence of solvation on ions in nanotubes and slits, including transport in these structures. Another topic is the effect of doping of carbon tubes on their ability to screen an external field, which influences the capacity.Our general aim is to obtain the basic properties of the nanosystems and the interaction between the various particles from DFT, and use them to describe ensembles of particles in a grand-canonical formalism, in which both the interfacial charge and changes in the electrode potential are well defined.We have agreed to cooperate with two experimental groups: Prof. Kaiser, Ulm, who investigates carbon structures with high-resolution transmission electron microscopy, and Prof. Unwin, Warwick, who can investigate electrochemical processes with ultra-high resolution.We are principally interested in the fundamental properties of these confined systems: the distribution of particles and of the electrostatic potential; their capacity to store charge; their equilibrium with a bulk solution. The systems we investigate can be used in supercapacitors and in lithium ion batteries.