Ionic liquid near a charged wall

structure and capacitance of electrical double layer

Maxim V. Fedorov, Alexei A. Kornyshev

Research output: Contribution to journalArticle

294 Citations (Scopus)

Abstract

We study the effects of ion size asymmetry and short-range correlations on the electrical double layer in ionic liquids: we perform molecular dynamics simulations of a model ionic liquid between two "electrodes" and calculate the differential capacitance of each as a function of the electrode potential. The capacitance curve has an asymmetric "bell-shape" character, in qualitative agreement with recent experiments and the mean-field theory (MFT) which takes into account the limitation on the maximal local density of ions. The short-range ionic correlations, not included in the MFT, lead to an overscreening effect which changes radically the structure of the double layer at small and moderate charging. With the radius of cations taken to be twice as large as anions, the position of the main capacitance maximum is shifted positively from the potential of zero charge (PZC), as predicted by MFT. An extension of the theory (EMFT), however, reproduces the simulated capacitance curve almost quantitatively. Capacitance curves for real ionic liquids will be affected by nonspherical shape of ions and sophisticated pair potentials, varying from liquid to liquid. But understanding the capacitance behavior of such model system is a basis for rationalizing those more specific features.

Original languageEnglish
Pages (from-to)11868-11872
Number of pages5
JournalJournal of Physical Chemistry B
Volume112
Issue number38
DOIs
Publication statusPublished - 26 Aug 2008

Fingerprint

Ionic Liquids
Ionic liquids
Capacitance
capacitance
Mean field theory
liquids
Ions
curves
ions
Electrodes
electrodes
Liquids
bells
Anions
charging
Molecular dynamics
Cations
Negative ions
Positive ions
asymmetry

Keywords

  • molecular dynamics
  • differential capacitance
  • temperature
  • electrochemistry
  • electrolytes
  • simulations

Cite this

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abstract = "We study the effects of ion size asymmetry and short-range correlations on the electrical double layer in ionic liquids: we perform molecular dynamics simulations of a model ionic liquid between two {"}electrodes{"} and calculate the differential capacitance of each as a function of the electrode potential. The capacitance curve has an asymmetric {"}bell-shape{"} character, in qualitative agreement with recent experiments and the mean-field theory (MFT) which takes into account the limitation on the maximal local density of ions. The short-range ionic correlations, not included in the MFT, lead to an overscreening effect which changes radically the structure of the double layer at small and moderate charging. With the radius of cations taken to be twice as large as anions, the position of the main capacitance maximum is shifted positively from the potential of zero charge (PZC), as predicted by MFT. An extension of the theory (EMFT), however, reproduces the simulated capacitance curve almost quantitatively. Capacitance curves for real ionic liquids will be affected by nonspherical shape of ions and sophisticated pair potentials, varying from liquid to liquid. But understanding the capacitance behavior of such model system is a basis for rationalizing those more specific features.",
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Ionic liquid near a charged wall : structure and capacitance of electrical double layer. / Fedorov, Maxim V.; Kornyshev, Alexei A.

In: Journal of Physical Chemistry B, Vol. 112, No. 38, 26.08.2008, p. 11868-11872.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Ionic liquid near a charged wall

T2 - structure and capacitance of electrical double layer

AU - Fedorov, Maxim V.

AU - Kornyshev, Alexei A.

PY - 2008/8/26

Y1 - 2008/8/26

N2 - We study the effects of ion size asymmetry and short-range correlations on the electrical double layer in ionic liquids: we perform molecular dynamics simulations of a model ionic liquid between two "electrodes" and calculate the differential capacitance of each as a function of the electrode potential. The capacitance curve has an asymmetric "bell-shape" character, in qualitative agreement with recent experiments and the mean-field theory (MFT) which takes into account the limitation on the maximal local density of ions. The short-range ionic correlations, not included in the MFT, lead to an overscreening effect which changes radically the structure of the double layer at small and moderate charging. With the radius of cations taken to be twice as large as anions, the position of the main capacitance maximum is shifted positively from the potential of zero charge (PZC), as predicted by MFT. An extension of the theory (EMFT), however, reproduces the simulated capacitance curve almost quantitatively. Capacitance curves for real ionic liquids will be affected by nonspherical shape of ions and sophisticated pair potentials, varying from liquid to liquid. But understanding the capacitance behavior of such model system is a basis for rationalizing those more specific features.

AB - We study the effects of ion size asymmetry and short-range correlations on the electrical double layer in ionic liquids: we perform molecular dynamics simulations of a model ionic liquid between two "electrodes" and calculate the differential capacitance of each as a function of the electrode potential. The capacitance curve has an asymmetric "bell-shape" character, in qualitative agreement with recent experiments and the mean-field theory (MFT) which takes into account the limitation on the maximal local density of ions. The short-range ionic correlations, not included in the MFT, lead to an overscreening effect which changes radically the structure of the double layer at small and moderate charging. With the radius of cations taken to be twice as large as anions, the position of the main capacitance maximum is shifted positively from the potential of zero charge (PZC), as predicted by MFT. An extension of the theory (EMFT), however, reproduces the simulated capacitance curve almost quantitatively. Capacitance curves for real ionic liquids will be affected by nonspherical shape of ions and sophisticated pair potentials, varying from liquid to liquid. But understanding the capacitance behavior of such model system is a basis for rationalizing those more specific features.

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KW - temperature

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KW - electrolytes

KW - simulations

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JO - Journal of Physical Chemistry B

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