Maison de la Simulation, CEA, CNRS, Université Paris-Sud, UVSQ, Université Paris-Saclay, 91191 Gif-sur-Yvette, France.
Sorbonne Université, CNRS, Physico-Chimie des Électrolytes et Nanosystèmes Interfaciaux, PHENIX, F-75005 Paris, France.
J Chem Phys. 2018 May 21;148(19):193812. doi: 10.1063/1.5012761.
When an ionic liquid adsorbs onto a porous electrode, its ionic arrangement is deeply modified due to a screening of the Coulombic interactions by the metallic surface and by the confinement imposed upon it by the electrode's morphology. In particular, ions of the same charge can approach at close contact, leading to the formation of a superionic state. The impact of an electrified surface placed between two liquid phases is much less understood. Here we simulate a full supercapacitor made of the 1-butyl-3-methylimidazolium hexafluorophosphate and nanoporous graphene electrodes, with varying distances between the graphene sheets. The electrodes are held at constant potential by allowing the carbon charges to fluctuate. Under strong confinement conditions, we show that ions of the same charge tend to adsorb in front of each other across the graphene plane. These correlations are allowed by the formation of a highly localized image charge on the carbon atoms between the ions. They are suppressed in larger pores, when the liquid adopts a bilayer structure between the graphene sheets. These effects are qualitatively similar to the recent templating effects which have been reported during the growth of nanocrystals on a graphene substrate.
当离子液体吸附在多孔电极上时，由于金属表面的屏蔽作用和电极形态对其的限制，其离子排列会发生深刻的变化。特别是，相同电荷的离子可以接近并紧密接触，从而形成超离子态。然而，对于放置在两个液相之间的带电表面的影响，我们的了解要少得多。在这里，我们模拟了一个由 1-丁基-3-甲基咪唑六氟磷酸盐和纳米多孔石墨烯电极组成的全超级电容器，其中石墨烯片之间的距离不同。通过允许碳原子的电荷波动，电极被保持在恒定的电势下。在强烈的限制条件下，我们表明相同电荷的离子倾向于在石墨烯平面上相互吸附。这种相关性是通过在离子之间的碳原子上形成高度局域化的镜像电荷来允许的。当液体在石墨烯片之间采用双层结构时，这种相关性在较大的孔中被抑制。这些效应与最近在石墨烯衬底上生长纳米晶体时报道的模板效应在性质上相似。
