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Nanostructure of the Ionic Liquid-Graphite Stern Layer

Elbourne, A.; McDonald, S.; Voïtchovsky, K.; Endres, F.; Warr, G.G.; Atkin, R.

Nanostructure of the Ionic Liquid-Graphite Stern Layer Thumbnail


A. Elbourne

S. McDonald

F. Endres

G.G. Warr

R. Atkin


Ionic liquids (ILs) are attractive solvents for devices such as lithium ion batteries and capacitors, but their uptake is limited, partially because their Stern layer nanostructure is poorly understood compared to molecular solvents. Here, in situ amplitude-modulated atomic force microscopy has been used to reveal the Stern layer nanostructure of the 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIm TFSI)–HOPG (highly ordered pyrolytic graphite) interface with molecular resolution. The effect of applied surface potential and added 0.1 wt/wt % Li TFSI or EMIm Cl on ion arrangements is probed between ±1 V. For pure EMIm TFSI at open-circuit potential, well-defined rows are present on the surface formed by an anion–cation–cation–anion (A–C–C–A) unit cell adsorbed with like ions adjacent. As the surface potential is changed, the relative concentrations of cations and anions in the Stern layer respond, and markedly different lateral ion arrangements ensue. The changes in Stern layer structure at positive and negative potentials are not symmetrical due to the different surface affinities and packing constraints of cations and anions. For potentials outside ±0.4 V, images are featureless because the compositional variation within the layer is too small for the AFM tip to detect. This suggests that the Stern layer is highly enriched in either cations or anions (depending on the potential) oriented upright to the surface plane. When Li+ or Cl– is present, some Stern layer ionic liquid cations or anions (respectively) are displaced, producing starkly different structures. The Stern layer structures elucidated here significantly enhance our understanding of the ionic liquid electrical double layer.


Elbourne, A., McDonald, S., Voïtchovsky, K., Endres, F., Warr, G., & Atkin, R. (2015). Nanostructure of the Ionic Liquid-Graphite Stern Layer. ACS Nano, 9(7), 7608-7620.

Journal Article Type Article
Acceptance Date Jun 6, 2015
Online Publication Date Jun 6, 2015
Publication Date Jul 28, 2015
Deposit Date Jun 23, 2015
Publicly Available Date Jun 6, 2016
Journal ACS Nano
Print ISSN 1936-0851
Electronic ISSN 1936-086X
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 9
Issue 7
Pages 7608-7620
Keywords Ionic liquids, Amplitude-modulated atomic force microscopy, Surface chemistry, Self-assembly, Adsorption.


Accepted Journal Article (3.7 Mb)

Copyright Statement
This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Nano, copyright © 2015 American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see

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