Issue 38, 2015

Weighing the surface charge of an ionic liquid


Electrochemical quartz crystal microbalance has been used to measure changes in the composition of the capacitive electrical double layer for 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)-trifluorophosphate, an ionic liquid, in contact with a gold electrode surface as a function of potential. The mass difference between the cation and anion means that the technique can effectively “weigh” the surface charge accurately with high temporal resolution. This reveals quantitatively how changing the potential alters the ratio of cations and anions associated with the electrode surface, and thus the charge per unit area, as well as the kinetics associated with these interfacial processes. The measurements reveal that it is diffusion of co-ions into the interfacial region rather than expulsion of counterions that controls the relaxation. The measured potential dependent double layer capacitance experimentally validates recent theoretical predictions for counterion overscreening (low potentials) and crowding (high potentials) at electrode surfaces. This new capacity to quantitatively measure ion composition is critical for ionic liquid applications ranging from batteries, capacitors and electrodeposition through to boundary layer structure in tribology, and more broadly provides new insight into interfacial processes in concentrated electrolyte solutions.

Graphical abstract: Weighing the surface charge of an ionic liquid

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Article information

Article type
16 Jun 2015
03 Sep 2015
First published
09 Sep 2015
This article is Open Access
Creative Commons BY license

Nanoscale, 2015,7, 16039-16045

Author version available

Weighing the surface charge of an ionic liquid

N. Hjalmarsson, D. Wallinder, S. Glavatskih, R. Atkin, T. Aastrup and M. W. Rutland, Nanoscale, 2015, 7, 16039 DOI: 10.1039/C5NR03965G

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