On the thickness of the double layer in ionic liquids

TL;DR

This paper investigates the thickness of the electrical double layer in ionic liquids using DFT and MD simulations, focusing on ion layering and capacitance behavior at the Au(111) surface.

Contribution

It combines DFT and MD approaches to analyze the EDL structure and challenges the traditional single-layer assumption in ionic liquids.

Findings

Capacitance-potential dependence characterized for the Helmholtz model

MD simulations reveal multilayer ion structuring in the EDL

Results suggest the EDL may be multi-ionic-layer thick

Abstract

In this study, we examined the thickness of the electrical double layer (EDL) in ionic liquids using density functional theory (DFT) calculations and molecular dynamics (MD) simulations. We focused on the BF4- anion adsorption from 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) ionic liquid on the Au(111) surface. At both DFT and MD levels, we evaluated the capacitance-potential dependence for the Helmholtz model of the interface. Using MD simulations, we also explored a more realistic, multilayer EDL model accounting for the ion layering. Concurrent analysis of the DFT and MD results provides a ground for thinking whether the electrical double layer in ionic liquids is one- or multi-ionic-layer thick.