Interfacial Layering in the Electric Double Layer of Ionic Liquids

Abstract

Ions in ionic liquids and concentrated electrolytes reside in a crowded, strongly interacting environment, leading to the formation of discrete layers of charges at interfaces and spin-glass structure in the bulk. Here, we propose a simple theory that captures the coupling between steric and electrostatic forces in ionic liquids. The theory predicts the formation of discrete layers of charge at charged interfaces. Further from the interface, or at low polarization of the electrode, the model outputs slowly decaying oscillations in the charge density with a wavelength of a single ion diameter, as shown by analysis of the gradient expansion. The gradient expansion suggests a new structure for partial differential equations describing the electrostatic potential at charged interfaces. We find quantitative agreement between the theory and molecular simulations in the differential capacitance and concentration profiles.

Ion correlations drive charge overscreening and heterogeneous nucleation at solid–aqueous electrolyte interfaces

“…2 B ). We note that this alternating layer structure is similar to the oscillatory structure of ionic liquids observed at charged interfaces ( 35 , 36 ), where the formation of discrete layers of charge is controlled by the balance between steric and electrostatic forces between ionic species ( 37 , 38 ).…”

“…This observation is unexpected from ion-ion correlation theories (2-4) for aqueous solutions in which positional correlations between monovalent ions are typically assumed to be negligible. The observed multilayer structure is analogous to the oscillatory structure of ionic liquids developed at charged interfaces in solvent-free systems (35)(36)(37)(38). Here, the correlations between monovalent ions is enhanced at elevated ion concentration (i.e., low water content) near the highly charged surface.…”

Chiral Biobased Ionic Liquids with Cations or Anions including Bile Acid Building Blocks as Chiral Selectors in Voltammetry

“…[3][4][5][6][7] Very recent studies point to CILs, or even ILs with chiral additives, being of huge interest as chiral media for enantioselective electrochemistry and electroanalysis, too. [8][9][10][11] Actually, ILs are known to result in much higher and longer-range order at the electrode j solution interphase respect to the double layer structure of "classical" solvent + supporting electrolyte systems, [12][13][14][15][16][17][18][19][20][21][22][23][24] a peculiarity still holding in the presence of significant water amounts; [18] this feature can be regarded as an attractive tool for achieving high control in electron transfer processes, for both analytical and preparative applications. In particular, in the case of CILs such high order can promote effective transmission of the chiral information.…”

Phase Transitions and Electrochemical Properties of Ionic Liquids and Ionic Liquid—Solvent Mixtures

“…The scaling behavior was observed for a number of simple salts (NaCl, LiCl, Kl, CsCl) in water, and for 1-butyl-1-methylpyrrolidinium bis[(trifluoromethyl)sulfonyl]imide ([C4C1Pyrr][NTf2]) in a number of solvents (propylene carbonate, dimethyl sulfoxide, acetonitrile, anhydrous benzonitrile), as well as for pure ILs [C2mim][NTf2] and [C3mim][NTf2] (in the latter case, the temperature dependence was verified). A scaling law for the screening length has been confirmed in theories based on different assumptions [ 136 , 137 , 138 , 139 , 140 , 141 ] and in all-atom molecular dynamics simulations [ 142 , 143 ]. The scaling exponents, however, appeared to be significantly lower than the experimentally measured one.…”