Montes-Campos Hadrián, Otero-Mato José Manuel, Méndez-Morales Trinidad, Cabeza Oscar, Gallego Luis J, Ciach Alina, Varela Luis M
Grupo de Nanomateriales, Fotónica y Materia Blanda, Departamentos de Física de Partículas y Física Aplicada, Facultade de Física, Universidade de Santiago de Compostela, Campus Vida s/n, E-15782 Santiago de Compostela, Spain.
Phys Chem Chem Phys. 2017 Sep 20;19(36):24505-24512. doi: 10.1039/c7cp04649a.
We perform molecular dynamics simulations of ionic liquids confined between graphene walls under a large variety of conditions (pure ionic liquids, mixtures with water and alcohols, mixtures with lithium salts and defective graphene walls). Our results show that the formation of striped and hexagonal patterns in the Stern layer can be considered as a general feature of ionic liquids at electrochemical interfaces, the transition between patterns being controlled by the net balance of charge in the innermost layer of adsorbed molecules. This explains previously reported experimental and computational results and, for the first time, why these pattern changes are triggered by any perturbation of the charge density at the innermost layer of the electric double layer (voltage and composition changes, and vacancies at the electrode walls, among others), which may help tuning electrode-ionic liquid interfaces. Using Monte Carlo simulations we show that such structures can be reproduced by a simple two-dimensional lattice model with only nearest-neighbour interactions, governed by highly screened ionic interactions and short-range and excluded volume interactions. We also show that the results of our simulations are consistent with those inferred from the Landau-Brazovskii theory of pattern formation in self-assembling systems. The presence of these patterns at the ionic liquid graphene-electrode interfaces may have a strong impact on the process of ionic transfer from the bulk mixtures to the electrodes, on the differential capacitance of the electrode-electrolyte double layer or on the rates of redox reactions at the electrodes, among other physicochemical properties, and is therefore an effect of great technological interest.
我们在多种条件下（纯离子液体、与水和醇的混合物、与锂盐的混合物以及有缺陷的石墨烯壁）对限制在石墨烯壁之间的离子液体进行了分子动力学模拟。我们的结果表明，斯特恩层中条纹和六边形图案的形成可被视为离子液体在电化学界面的一个普遍特征，图案之间的转变由吸附分子最内层电荷的净平衡控制。这解释了先前报道的实验和计算结果，并且首次说明了为什么这些图案变化是由双电层最内层电荷密度的任何扰动（电压和组成变化、电极壁上的空位等）引发的，这可能有助于调节电极 - 离子液体界面。通过蒙特卡罗模拟我们表明，这样的结构可以由一个仅具有最近邻相互作用的简单二维晶格模型重现，该模型由高度屏蔽的离子相互作用以及短程和排除体积相互作用控制。我们还表明，我们的模拟结果与从自组装系统中图案形成的朗道 - 布拉佐夫斯基理论推断出的结果一致。这些图案在离子液体 - 石墨烯 - 电极界面的存在可能对离子从本体混合物转移到电极的过程、电极 - 电解质双层的微分电容或电极上氧化还原反应的速率等其他物理化学性质产生强烈影响，因此是一个具有重大技术意义的效应。
