Interfaces between Charged Surfaces and Ionic Liquids: Insights from Molecular Simulations

Abstract

MD simulations of ionic liquid–electrode interfaces show that a transition from a multilayer ion structure to an ordered monolayer structure can be observed at certain values of the surface charge density. Upon this transition, a distinct change in the surface charge excess in the first two interfacial layers can be seen as a function of the renormalized surface charge density. The degree of ordering in the innermost ion layer increases upon increasing the surface charge density, while the transition region exhibits systematic transformations upon surface charging. The point of maximum layering in the transition region depends on the density of the ionic liquid as well as on the ion-ion and ion–electrode interactions. We suggest that the surface charge densities that correspond κIon≈1 (and consequently to the regime of monolayer formation) can be used as “landmark” points for qualitative and quantitative comparison of theoretical, simulations and experimental data on ionic liquids structure at charged surfaces

Poly(a)morphic portrait of the electrical double layer in ionic liquids

“…[11,14], we define a unified κ-scale, where the surface charge density (σ) is normalised by the maximum charge density that can be stored in a densely packed counter-ion monolayer (θ max Ion ):…”

“…[14] it has been suggested that these trends may be universal and are expected to be found in many IL systems (see also [17]). However, this hypothesis is based on theories and models that do not take into account molecular-scale effects of ion geometry and heterogeneous partial charge distribution across the IL molecules, and overall it remains unclear whether the conclusions from the Refs.…”

“…However, this hypothesis is based on theories and models that do not take into account molecular-scale effects of ion geometry and heterogeneous partial charge distribution across the IL molecules, and overall it remains unclear whether the conclusions from the Refs. [7,11,14] are not effects of an oversimplified view on ILs.…”

“…Charge/voltage driven structural transitions in the electrical double layer (EDL) in ionic liquids (ILs) have recently attracted large interest in experimental [1,2,3,4,5,6], theoretical [7] and computational [8,9,10,11,12,13,14] communities due to the importance of this subject for a variety of IL applications [15,16].…”

Static Capacitance at the Electrochemical Liquid-liquid Interface Between Ionic Liquids and Eutectic Ga-In Alloy Measured Using the Pendant Drop Method

“…BF À 4 ions, accumulated at E > E pzc , are smaller than the imidazolium cations, C 2 mim + and C 8 mim + . In order to occupy the EDL and to govern the C dc behavior, smaller ions need greater «q«, 83 and also greater «E ¹ E pzc « unless the existence of small ions leads to extraordinarily high C dc . Therefore the smaller BF Fig.…”