Classical Density Functional Study on Interfacial Structure and Differential Capacitance of Ionic Liquids near Charged Surfaces

Ma, Ke; Woodward, Clifford E.; Forsman, Jan

doi:10.1021/jp504001u

Cited by 35 publications

(20 citation statements)

References 37 publications

(128 reference statements)

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“…Across all degrees of ion pairing, the DC tends to be higher at a positive electrode potential compared to a negative one. The larger DC at the positive electrode is generally attributed to the greater ability of the smaller anion to screen surface charges [38]. However, a monotonic decrease is observed for the DC in general, across a wide potential range, with increasing amounts of ion pairing (Fig.11).…”

Section: Forces Between Charged Surfacesmentioning

confidence: 92%

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Influence of ion pairing in ionic liquids on electrical double layer structures and surface force using classical density functional approach

Forsman

Woodward

2015

The Journal of Chemical Physics

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We explore the influence of ion pairing in room temperature ionic liquids confined by planar electrode surfaces. Using a coarse-grained model for the aromatic ionic liquid [C4MIM+][BF4−], we account for an ion pairing component as an equilibrium associating species within a classical density functional theory. We investigated the resulting structure of the electrical double layer as well as the ensuing surface forces and differential capacitance, as a function of the degree of ion association. We found that the short-range structure adjacent to surfaces was remarkably unaffected by the degree of ion pairing, up to several molecular diameters. This was even the case for 100% of ions being paired. The physical implications of ion pairing only become apparent in equilibrium properties that depend upon the long-range screening of charges, such as the asymptotic behaviour of surface forces and the differential capacitance, especially at low surface potential. The effect of ion pairing on capacitance is consistent with their invocation as a source of the anomalous temperature dependence of the latter. This work shows that ion pairing effects on equilibrium properties are subtle and may be difficult to extract directly from simulations.

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Section: Forces Between Charged Surfacesmentioning

confidence: 92%

“…The parameter λ is determined by electroneutrality in the bulk (as the correlation hole represents the removal of the self contribution from the background) [30,38]. Unlike ion correlations are approximated with the functional,…”

Section: Electrostatic Correlationsmentioning

confidence: 99%

Influence of ion pairing in ionic liquids on electrical double layer structures and surface force using classical density functional approach

Forsman

Woodward

2015

The Journal of Chemical Physics

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“…Differential capacitance is directly related to the capacity of EDLCs. A simulation of the electrode | IL interface was done to correlate the change of differential capacitance with surface potential (Vatamanu et al, 2010; Ma et al, 2014). It was also found that small ions, like Li + , in an IL solution will change the original ionic composition of the IL and construct different electrode | IL interfaces leading to a smaller differential capacitance compared with the one of the neat IL (Zhao et al, 2010).…”

Section: Supercapacitorsmentioning

confidence: 99%

Ionic Liquid-Based Electrolytes for Supercapacitor and Supercapattery

Chen

2019

Front. Chem.

162

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There is a strong desire to replace or complement aqueous and organic electrolytes by ionic liquids (ILs) in electrochemical energy storage (EES) devices to achieve high operating voltages and hence high energy capacity. ILs are regarded as the inherent and competitive electrolytes since they were introduced to the electrochemical research community because they can overcome many disadvantages of the conventional aqueous and organic electrolytes, such as narrow potential windows, volatility, and flammability. This paper reviews critically the recent literatures of IL-based electrolytes used in supercapacitor, supercapattery, and micro-supercapacitor. Supercapattery is a generic term for various hybrid devices combining the merits of rechargeable battery and supercapacitor and often shows capacitive behavior. Fundamentals of supercapattery are briefly explained with typical examples. Micro-supercapacitor falls in the same scope of supercapacitor and supercapattery and shares the same fundamental concerns besides topology or structure. The future of IL-based electrolytes for the capacitive EES devices are also prospected.

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“…Despite a large amount of theoretical and simulation work on the capacitance of RTILs in porous electrodes, ,− little is known about how the properties of EDLCs containing RTIL mixtures would be affected by the electrolyte composition. − Toward the rational design of the electrolytes and electrode materials, it would be desirable to understand the following: How would the EDL structure and capacitance change with the composition of RTIL mixtures? What is the microscopic mechanism underlying the capacitance change?…”

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confidence: 99%

Enhancing the Capacitive Performance of Electric Double-Layer Capacitors with Ionic Liquid Mixtures

et al. 2016

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Formulating room-temperature ionic liquid (RTIL) mixed electrolytes was recently proposed as an effective and convenient strategy to increase the capacitive performance of electrochemical capacitors. Here we investigate the electrical double-layer (EDL) structure and the capacitance of two RTILs, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4), and their mixtures with onion-like carbon electrodes using experiment and classical density functional theory. The principal difference between these ionic liquids is the smaller diameter of the BF4 – anion relative to the TFSI– anion and the EMI+ cation. A volcano-shaped trend is identified for the capacitance versus the composition of the RTIL mixture. The mixture effect, which makes more counterions pack on and more co-ions leave from the electrode surface, leads to an increase of the counterion density within the EDL and thus a larger capacitance. These theoretical predictions are in good agreement with our experimental observations and offer guidance for designing RTIL mixtures for EDL supercapacitors.

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Classical Density Functional Study on Interfacial Structure and Differential Capacitance of Ionic Liquids near Charged Surfaces

Cited by 35 publications

References 37 publications

Influence of ion pairing in ionic liquids on electrical double layer structures and surface force using classical density functional approach

Influence of ion pairing in ionic liquids on electrical double layer structures and surface force using classical density functional approach

Ionic Liquid-Based Electrolytes for Supercapacitor and Supercapattery

Enhancing the Capacitive Performance of Electric Double-Layer Capacitors with Ionic Liquid Mixtures

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