Quantum design of ionic liquids for extreme chemical inertness and a new theory of the glass transition

Fletcher, Stephen; Black, Victoria Jane; Kirkpatrick, Iain; Varley, Thomas S.

doi:10.1007/s10008-012-1974-2

Cited by 18 publications

(34 citation statements)

References 63 publications

(35 reference statements)

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“…High-temperature supercapacitors were constructed inhouse using the method of [95]. Briefly, the electrodes were made by a screen printing method (DEK 65 manual screen printer, DEK Printing Machines Ltd, Weymouth, UK) and consisted of three printed layers.…”

Section: Methodsmentioning

confidence: 99%

“…Hence, in this case, the pore channels containing aqueous sulphuric acid are more resistive than the pore walls by a factor of circa 70. The situation is even more extreme in the case of high-temperature supercapacitors [95], which utilize ionic liquids such as butyltrimethylammonium bis(trifluoromethylsulfonyl)imide. This latter compound has a room-temperature conductivity of only 2.1×10 −3 S/cm, implying that the pore channels containing ionic liquid are more resistive than the pore walls by a factor of 30,000 or so.…”

Section: Electrochemical Equivalent Circuit Of Carbon-based Supercapamentioning

confidence: 99%

“…For example, the resistivity of butyltrimethylammonium bis(trifluoromethylsulfonyl)imide (BTM) decreases from 476 Ω cm at 25°C to 17.5 Ω cm at 200°C, a factor of nearly 30 [95]. This precipitous fall causes a dramatic lowering of the RC time constants of the pores and results in a doubling of the equivalent series capacitance of hightemperature supercapacitors [95].…”

Section: Comparison Of Theory and Experimentsmentioning

confidence: 99%

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A universal equivalent circuit for carbon-based supercapacitors

Fletcher

Black

Kirkpatrick

2013

J Solid State Electrochem

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133

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A universal equivalent circuit is proposed for carbon-based supercapacitors. The circuit, which actually applies to all porous electrodes having non-branching pores, consists of a single vertical ladder network in series with an RC parallel network. This elegant arrangement explains the three most important shortcomings of present-day supercapacitors, namely open circuit voltage decay, capacitance loss at high frequency, and voltammetric distortion at high scan rate. It also explains the shape of the complex plane impedance plots of commercial devices and reveals why the equivalent series capacitance increases with temperature. Finally, the construction of a solid-state supercapacitor simulator is described. This device is based on a truncated version of the universal equivalent circuit, and it allows experimenters to explore the responses of different supercapacitor designs without having to modify real supercapacitors.

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Section: Methodsmentioning

confidence: 99%

Section: Electrochemical Equivalent Circuit Of Carbon-based Supercapamentioning

confidence: 99%

Section: Comparison Of Theory and Experimentsmentioning

confidence: 99%

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A universal equivalent circuit for carbon-based supercapacitors

Fletcher

Black

Kirkpatrick

2013

J Solid State Electrochem

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133

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“…2,[9][10][11][12]22,23 The increased stability was attributed to the higher blocking and shielding effect and increased electron donating characteristics of larger alkyl groups. 9,11,22 In contrast, no substantial improvement in the cathodic stability of quaternary ammonium ions was observed in another study upon increasing the length of the alkyl substituent.…”

Section: -15mentioning

confidence: 99%

Electrochemical Stability of Quaternary Ammonium Cations: An Experimental and Computational Study

Mousavi

Kashefolgheta

Stein

et al. 2015

J. Electrochem. Soc.

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Quaternary ammonium ions, NR 4 + , are among the most electrochemically stable organic cations. Because of their wide electrochemical windows, they are frequently used in batteries and electrochemical capacitors. Improving the electrochemical stability and expanding the electrochemical windows of quaternary ammonium ion is highly desired. In this work, we investigated the electrochemical stability of quaternary ammonium ions and showed that the chain length, type (primary vs. secondary), size, and steric hindrance of the saturated alkyl substituents have only a very small effect (less than 150 mV) on their electrochemical stability toward reduction. To provide a molecular understanding of substituent effects on electrochemical stability, quantum calculations were performed employing density functional theory, and it was shown that the structure of saturated aliphatic alkyl substituents has only minimal effects on the electronic environment around the positive nitrogen center and the LUMO energy level of quaternary ammonium cations. Moreover, a linear correlation between the cathodic limit and the LUMO energy levels of the NR 4 + , N-butylpyridinium, and 1-ethyl-3-methylimidazolium ions was found, suggesting that electrochemical stabilities of new cations may be computationally predicted on the basis of LUMO energies of these systems. With the increasing global demand for energy, improving existing energy storage technologies is as critical as developing more efficient methods for energy production. For one important class of energy storage technologies, namely electrical energy storage, the energy density of a device is usually limited by the voltage window in which the device can function. Therefore, expanding the working voltage range of such devices is highly desired. The electrochemical decomposition of electrolytes, which are commonly used in energy storage devices such as electrochemical capacitors, often limits the useful voltage window 1 because these devices can function properly only within the electrochemical window of their electrolyte. Modifying the structure of electrolytes and improving their electrochemical stabilities has been the focus of numerous studies to date. [2][3][4][5][6][7][8][9][10][11][12][13][14][15] The electrochemical window of an electrolyte is the voltage range in which the electrolyte is chemically stable and does not get reduced or oxidized as a result of the applied potential. 16 The upper end of the electrochemical window is usually limited by the oxidation of the anion, and the lower end of the electrochemical window is determined by the reduction of the cation. 1 One of the most electrochemically stable classes of organic cations comprises the quaternary ammonium ions, NR 4 + . These are highly inert toward reduction, offer wide electrochemical windows, and are, therefore, frequently used in batteries and capacitors. 2,5,6,17 Much research has been devoted to improving the electrochemical stability of quaternary ammonium ions. 4,[9][10][11][12][13][14][15] Reduction of qua...

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“…Pt + H + + e − → PtH upd (5) Room temperature ionic liquids (RTILs) are materials that are composed entirely of ions and which are liquid below 100 °C (although we note that a proposal to increase the temperature in this definition was recently published 27 ). 28 Due to their unique properties, such as wide electrochemical windows, inherent conductivities, and thermal stabilities, the electrochemical applications of RTILs have increased significantly in recent years and include fundamental studies of mass-and charge-transfer dynamics, 29 and uses as electrolytes in devices such as fuel cells, batteries and supercapacitors.…”

mentioning

confidence: 99%

Hydrogen Electrooxidation under Conditions of High Mass Transport in Room-Temperature Ionic Liquids and the Role of Underpotential-Deposited Hydrogen

Goodwin

Walsh

2016

J. Phys. Chem. C

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. (2016) Hydrogen electrooxidation under conditions of high mass transport in room-temperature ionic liquids and the role of underpotential-deposited hydrogen. Journal of Physical Chemistry C, 120 (21). pp. 11498-11507. ISSN 1932-7455 Access from the University of Nottingham repository: http://eprints.nottingham.ac.uk/33911/1/Article%20jp-2016-01592f.R2.pdf Copyright and reuse:The Nottingham ePrints service makes this work by researchers of the University of Nottingham available open access under the following conditions. This article is made available under the University of Nottingham End User licence and may be reused according to the conditions of the licence. For more details see: http://eprints.nottingham.ac.uk/end_user_agreement.pdf A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription. AbstractThe hydrogen oxidation reaction (HOR), an electrocatalytic reaction of fundamental and applied interest, was studied in the protic ionic liquid (PIL) diethylmethylammonium trifluoromethanesulfonate, [dema][TfO], at Pt electrodes using rotating disk electrode (RDE) and ultramicroelectrode (UME) voltammetry. A steady-state HOR current is observed during RDE voltammetry at overpotentials > 50 mV but an additional plateau is observed in the overpotential region 50-200 mV when using UMEs. The difference in voltammetric responses is attributed to higher rate of mass transport to the UME than to the RDE. Three models have been used to fit the experimental data. The first is a dual-pathway model, which assumes that the Tafel-Volmer and Heyrovsky-Volmer pathways are both active over the potential range of interest and no blockage of catalytic sites occurs during the reaction. The second is a dual-pathway model, which assumes that reaction intermediates block access of H 2 to catalytic sites. The third is based on the premise that underpotential-deposited hydrogen atoms (H upd ) can block adsorption and electrooxidation of H 2 at the Pt surface. While each model fits the polarisation curves reasonably well, detailed analysis suggests that the H updblocking model describes the responses better. To the best of our knowledge, this work is the first to demonstrate the advantages of UME voltammetry over RDE voltammetry for studying electrocatalytic reactions in PILs, and the first to show that H upd can inhibit an electrocatalytic reactions in an ionic liquid, a factor that may become important as the technological applications of these liquids increase.3

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Quantum design of ionic liquids for extreme chemical inertness and a new theory of the glass transition

Cited by 18 publications

References 63 publications

A universal equivalent circuit for carbon-based supercapacitors

A universal equivalent circuit for carbon-based supercapacitors

Electrochemical Stability of Quaternary Ammonium Cations: An Experimental and Computational Study

Hydrogen Electrooxidation under Conditions of High Mass Transport in Room-Temperature Ionic Liquids and the Role of Underpotential-Deposited Hydrogen

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