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Lai J, Zhang H, Xu K, Shi F. Linking Interfacial Structure and Electrochemical Behaviors of Batteries by High-Resolution Electrocapillarity. J Am Chem Soc 2024; 146:22257-22265. [PMID: 39013600 DOI: 10.1021/jacs.4c03791] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/18/2024]
Abstract
The electrode-electrolyte interface governs the kinetics and reversibility of all electrochemical processes. While theoretical models can calculate and simulate the structure and associated properties of this intriguing component, their validation by direct experimental measurement has been a long-standing challenge. Electrocapillarity is a classical technique that derives the interfacial structure through potential-dependent surface tensions, but its limited resolution has confined its application to ideal systems such as extremely diluted aqueous electrolytes. In this work, we revive this technique with unprecedented time resolution, which allows fast and precise extraction of intrinsic interfacial structure and properties for a wide spectrum of electrolytes, be it ideal or nonideal, aqueous or nonaqueous, dilute or superconcentrated. For the very first time, this new electrocapillarity enables the measurements of a set of interfacial quantities, such as ion concentration distribution and potential drop across Helmholtz planes. Applying it on Zn-battery electrolytes, we discovered that Cl- specific adsorption at the inner-Helmholtz plane results in unexpected Zn2+ aggregation at the outer-Helmholtz plane, and identified such a unique interfacial structure as the fundamental driving force for fast Zn deposition/stripping kinetics and crystallographic texturing. The renaissance of electrocapillarity brings a new tool to the understanding and design of new electrolytes for future battery systems.
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Affiliation(s)
- Jianwei Lai
- John and Willie Leone Family Department of Energy and Mineral Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Hanrui Zhang
- John and Willie Leone Family Department of Energy and Mineral Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Kang Xu
- SES AI Corporation, Woburn, Massachusetts 01801, United States
| | - Feifei Shi
- John and Willie Leone Family Department of Energy and Mineral Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, United States
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2
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Clarke OJR, Rowley A, Fox RV, Burgess IJ, Atifi A. Nano-Plasticity of an Electrified Ionic Liquid/Electrode Interface: Uncovering Hard-Soft Structuring via Controlled Metal Fill Factor. ACS NANO 2024; 18:14716-14725. [PMID: 38774972 DOI: 10.1021/acsnano.4c03617] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2024]
Abstract
Ionic liquids (ILs) nanostructuring at electrified interfaces is of both fundamental and practical interest as these materials are increasingly gaining prominence in energy storage and conversion processes. However, much remains unresolved about IL potential-controlled (re)organization under highly polarized interfaces, mostly due to the difficulty of selectively probing both the distal and proximal surface layers of adsorbed ions. In this work, the structural dynamics of the innermost layer (<10 nm from the surface) were independently interrogated from that of the ionic layers in the sub-surface region (>100 nm from the surface), using an infrared (IR) spectroscopy approach. By tuning the metal fill factor of gold films deposited on conductive metal oxide-modified IR internal reflection elements, the charge-driven (re)structuring of the inner and distal layers of 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate is unveiled. Within a relatively wide potential region (∼±1 V) bounding the potential of zero charges, the ionic liquid is shown to undergo a reversible (i.e., soft) reorganization whereby the innermost layer of anions (cations) is exchanged by a layer of cations (anions). Kinetically unhindered changes in the number density of constituent cations and anions largely follow electrostatic expectations in the subsurface region, whereas the innermost layer exhibits a pronounced hysteresis and very slow relaxation. Under larger negative potential bias, IL restructuring is characterized by a highly irreversible (i.e., hard) and intense interfacial densification of the BMPy+ cations, consistent with the formation of nanoscale segregated liquids. The outcomes of this work reveal a plastic IL nanostructuring under a strong electric field.
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Affiliation(s)
- Osai J R Clarke
- Department of Chemistry, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5C9, Canada
| | - Annabel Rowley
- Department of Chemistry, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5C9, Canada
| | - Robert V Fox
- Chemical Systems Department, Idaho National Laboratory, Idaho Falls, Idaho 83415, United States
| | - Ian J Burgess
- Department of Chemistry, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5C9, Canada
| | - Abderrahman Atifi
- Chemical Systems Department, Idaho National Laboratory, Idaho Falls, Idaho 83415, United States
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3
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Iwahashi T, Kishida H, Zhou W, Kim D, Ouchi Y. Activation Energy of Ion Desorption at Ionic Liquid/Pt Electrode Interfaces: A Sum-Frequency Generation Vibrational Spectroscopic Study. J Phys Chem B 2024; 128:5018-5029. [PMID: 38723200 DOI: 10.1021/acs.jpcb.4c00158] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/24/2024]
Abstract
Electrolyte/electrode interfaces of room-temperature ionic liquids (RTILs) exhibit hysteretic responses to different applied potentials owing to the differences in the ion adsorption/desorption processes; the ion desorption requires excess potential, which reflects the activation energy of ion desorption. Thus far, the contributions of the ion adsorption energy and the activation barrier for ion desorption toward the ion-dependent excess potential have not been quantified. Herein, we report on our infrared-visible sum-frequency generation vibrational spectroscopy study of the hysteretic responses of the anion adsorption/desorption at Pt electrode interfaces using neat, binary, and diluted RTILs composed of 1-butyl-3-methylimidazolium cations ([C4mim]+) and bis(trifluoromethanesulfonyl)amide ([TFSA]-) and trifluoromethanesulfonate ([OTf]-) anions. Experimental results are compared to the theoretical calculations for the electric double layer model. The hysteretic response of the RTIL/Pt interface derives predominantly from the activation energy of anion desorption, which causes the negative excess potential required for anion desorption. A comparison of the anion adsorption/desorption behaviors of neat RTILs with those of binary and diluted RTILs reveals that the large activation energy of anion desorption at the neat RTIL/Pt interface originates largely from the activation barrier for restructuring ionic layering in the diffuse layer.
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Affiliation(s)
- Takashi Iwahashi
- Department of Materials Science and Engineering, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152-8552, Japan
| | - Hibiki Kishida
- Department of Materials Science and Engineering, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152-8552, Japan
| | - Wei Zhou
- Department of Chemistry, Shanghai University, Shanghai 200444, China
| | - Doseok Kim
- Department of Physics, Sogang University, Seoul 04107, Republic of Korea
| | - Yukio Ouchi
- Department of Materials Science and Engineering, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152-8552, Japan
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MATSUI M, ORIKASA Y, UCHIYAMA T, NISHI N, MIYAHARA Y, OTOYAMA M, TSUDA T. Electrochemical In Situ/<i>operando</i> Spectroscopy and Microscopy Part 1: Fundamentals. ELECTROCHEMISTRY 2022. [DOI: 10.5796/electrochemistry.22-66093] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Affiliation(s)
| | - Yuki ORIKASA
- Department of Applied Chemistry, Ritsumeikan University
| | - Tomoki UCHIYAMA
- Department of Interdisciplinary Environment, Kyoto University
| | - Naoya NISHI
- Department of Energy and Hydrocarbon Chemistry, Kyoto University
| | - Yuto MIYAHARA
- Department of Energy and Hydrocarbon Chemistry, Kyoto University
| | - Misae OTOYAMA
- Research Institute of Electrochemical Energy, National Institute of Advanced Industrial Science and Technology (AIST)
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Zhang S, Nishi N, Katakura S, Sakka T. Evaluation of static differential capacitance at the [C 4mim +][TFSA -]/electrode interface using molecular dynamics simulation combined with electrochemical surface plasmon resonance measurements. Phys Chem Chem Phys 2021; 23:13905-13917. [PMID: 34132289 DOI: 10.1039/d1cp01435h] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Molecular dynamic (MD) simulations have been performed for 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C4mim+][TFSA-]), an ionic liquid (IL), on a charged graphene electrode to achieve the quantitative analysis of the static differential capacitance using the electrochemical surface plasmon resonance (ESPR). The MD simulations have provided the surface charge density on the electrode and ionic distributions in the electric double layer, both of which are indispensable for the evaluation of static differential capacitance using ESPR but are difficult to be measured by experimental techniques. This approach has allowed the quantitative analysis and explanation of the SPR angle shift in ESPR. The major contribution to the SPR angle shift is found to be the change in ionic concentrations of the first ionic layer on the electrode, owing to higher polarizabilities of ions in the first ionic layer than those in the overlayers. Moreover, the ionic orientation on the electrode and ionic multilayer structure have also been investigated in detail. The butyl group of C4mim+ in the first ionic layer is found to provide extra room for C4mim+ in the second ionic layer but exclude TFSA-, which affects the interval and regularity of ionic multilayers.
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Affiliation(s)
- Shiwei Zhang
- Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan.
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Zhang S, Nishi N, Sakka T. Electrochemical surface plasmon resonance measurements of camel-shaped static capacitance and slow dynamics of electric double layer structure at the ionic liquid/electrode interface. J Chem Phys 2020; 153:044707. [PMID: 32752680 DOI: 10.1063/5.0011671] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Electrochemical surface plasmon resonance (ESPR) is applied to evaluate the relative static differential capacitance at the interface between 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ionic liquid (IL) and a gold electrode, based on the relationship between the SPR angle and surface charge density on the electrode. Potential-step and potential-scan ESPR measurements are used to probe the dynamics of the electric double layer (EDL) structure that exhibit anomalously slow and asymmetrical characteristics depending on the direction of potential perturbation. EDL dynamics respond at least 30 times more slowly to changes of potential in the positive direction than in the negative direction. ESPR experiments with the positive-going potential scan are significantly affected by the slow dynamics even at a slow scan. The surface charge density that reflects the relative static capacitance is obtained from the negative-going potential scans. The evaluated quasi-static differential capacitance exhibits a camel-shaped potential dependence, thereby agreeing with the prediction of the mean-field lattice gas model of the EDL in ILs. ESPR is shown to be an effective experimental method for determining relative values of the static differential capacitance.
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Affiliation(s)
- Shiwei Zhang
- Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan
| | - Naoya Nishi
- Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan
| | - Tetsuo Sakka
- Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan
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Wang YL, Li B, Sarman S, Mocci F, Lu ZY, Yuan J, Laaksonen A, Fayer MD. Microstructural and Dynamical Heterogeneities in Ionic Liquids. Chem Rev 2020; 120:5798-5877. [PMID: 32292036 PMCID: PMC7349628 DOI: 10.1021/acs.chemrev.9b00693] [Citation(s) in RCA: 197] [Impact Index Per Article: 49.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2019] [Indexed: 12/11/2022]
Abstract
Ionic liquids (ILs) are a special category of molten salts solely composed of ions with varied molecular symmetry and charge delocalization. The versatility in combining varied cation-anion moieties and in functionalizing ions with different atoms and molecular groups contributes to their peculiar interactions ranging from weak isotropic associations to strong, specific, and anisotropic forces. A delicate interplay among intra- and intermolecular interactions facilitates the formation of heterogeneous microstructures and liquid morphologies, which further contributes to their striking dynamical properties. Microstructural and dynamical heterogeneities of ILs lead to their multifaceted properties described by an inherent designer feature, which makes ILs important candidates for novel solvents, electrolytes, and functional materials in academia and industrial applications. Due to a massive number of combinations of ion pairs with ion species having distinct molecular structures and IL mixtures containing varied molecular solvents, a comprehensive understanding of their hierarchical structural and dynamical quantities is of great significance for a rational selection of ILs with appropriate properties and thereafter advancing their macroscopic functionalities in applications. In this review, we comprehensively trace recent advances in understanding delicate interplay of strong and weak interactions that underpin their complex phase behaviors with a particular emphasis on understanding heterogeneous microstructures and dynamics of ILs in bulk liquids, in mixtures with cosolvents, and in interfacial regions.
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Affiliation(s)
- Yong-Lei Wang
- Department
of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Bin Li
- School
of Chemical Engineering and Technology, Sun Yat-sen University, Zhuhai 519082, P. R. China
| | - Sten Sarman
- Department
of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Francesca Mocci
- Department
of Chemical and Geological Sciences, University
of Cagliari, I-09042 Monserrato, Italy
| | - Zhong-Yuan Lu
- State
Key Laboratory of Supramolecular Structure and Materials, Institute
of Theoretical Chemistry, Jilin University, Changchun 130021, P. R. China
| | - Jiayin Yuan
- Department
of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Aatto Laaksonen
- Department
of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden
- State
Key Laboratory of Materials-Oriented and Chemical Engineering, Nanjing Tech University, Nanjing 210009, P. R. China
- Centre of
Advanced Research in Bionanoconjugates and Biopolymers, Petru Poni Institute of Macromolecular Chemistry Aleea Grigore Ghica-Voda, 41A, 700487 Iasi, Romania
- Department
of Engineering Sciences and Mathematics, Division of Energy Science, Luleå University of Technology, SE-97187 Luleå, Sweden
| | - Michael D. Fayer
- Department
of Chemistry, Stanford University, Stanford, California 94305, United States
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Katakura S, Nishi N, Kobayashi K, Amano KI, Sakka T. An electric double layer structure and differential capacitance at the electrode interface of tributylmethylammonium bis(trifluoromethanesulfonyl)amide studied using a molecular dynamics simulation. Phys Chem Chem Phys 2020; 22:5198-5210. [PMID: 32090216 DOI: 10.1039/c9cp05297f] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A molecular dynamics simulation at the electrode interface of a quaternary ammonium ionic liquid, tributylmethylammonium bis(trifluoromethanesulfonyl)amide ([N1444+][TFSA-]), has been performed. Unlike the commonly used cations, such as 1-alkyl-3-methylimidazolium and 1,1-alkylmethylpyrrolidinium cations, N1444+ has multiple long-alkyl groups (three butyl groups). The behavior of ions at the electrode interface, especially these butyl groups, has been investigated. N1444+ at the first layer mainly has two types of orientations, lying and standing. The lying orientation is dominant at moderately negative potentials. However, the standing one becomes dominant at the more negative potentials. Due to this orientational change, the number of N1444+ increases at the first layer as the potential becomes negative even at the potentials where the anions are completely depleted there. The change in orientation results in the upward deviation of the differential capacitance from the theoretical prediction at the negative potentials. The results suggest that the orientational preference caused by the steric constraint between alkyl groups plays an important role in the behavior of the electric double layer of the ionic liquids.
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Affiliation(s)
- Seiji Katakura
- Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan.
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9
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Kadis R. Can the equilibrium interfacial tensions be more in magnitude than non-equilibrium ones? Comment on “Electrocapillarity and zero-frequency differential capacitance at the interface between mercury and ionic liquids measured using the pendant drop method” by N. Nishi et al. [Phys. Chem. Chem. Phys., 2015, 17, 5219]. Chem Phys 2019. [DOI: 10.1016/j.chemphys.2018.09.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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10
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Kislenko SA, Moroz YO, Karu K, Ivaništšev VB, Fedorov MV. Calculating the Maximum Density of the Surface Packing of Ions in Ionic Liquids. RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A 2018. [DOI: 10.1134/s0036024418050187] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
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11
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Lucio AJ, Shaw SK. Effects and controls of capacitive hysteresis in ionic liquid electrochemical measurements. Analyst 2018; 143:4887-4900. [DOI: 10.1039/c8an01085d] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Capacitance vs. potential relationships help electrochemists better understand electrode–liquid interfacial behaviors.
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Affiliation(s)
| | - Scott K. Shaw
- Department of Chemistry
- University of Iowa
- Iowa City
- USA
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12
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NISHI N, KOJIMA Y, KATAKURA S, SAKKA T. Static Capacitance at the Electrochemical Liquid-liquid Interface Between Ionic Liquids and Eutectic Ga-In Alloy Measured Using the Pendant Drop Method. ELECTROCHEMISTRY 2018. [DOI: 10.5796/electrochemistry.17-00081] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Affiliation(s)
- Naoya NISHI
- Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University
| | - Yasuro KOJIMA
- Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University
| | - Seiji KATAKURA
- Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University
| | - Tetsuo SAKKA
- Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University
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13
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Iwasaki K, Yoshii K, Tsuda T, Kuwabata S. Physicochemical properties of phenyltrifluoroborate-based room temperature ionic liquids. J Mol Liq 2017. [DOI: 10.1016/j.molliq.2017.09.067] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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14
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Nishi N, Yasui S, Hashimoto A, Sakka T. Anion dependence of camel-shape capacitance at the interface between mercury and ionic liquids studied using pendant drop method. J Electroanal Chem (Lausanne) 2017. [DOI: 10.1016/j.jelechem.2017.02.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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15
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Vatamanu J, Vatamanu M, Borodin O, Bedrov D. A comparative study of room temperature ionic liquids and their organic solvent mixtures near charged electrodes. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:464002. [PMID: 27623976 DOI: 10.1088/0953-8984/28/46/464002] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The structural properties of electrolytes consisting of solutions of ionic liquids in a polar solvent at charged electrode surfaces are investigated using classical atomistic simulations. The studied electrolytes consisted of tetraethylammonium tetrafluoroborate (NEt4-BF4), 1-ethyl-3-methylimidazolium tetrafluoroborate (c2mim-BF4) and 1-octyl-3-methylimidazolium tetrafluoroborate (c8mim-BF4) salts dissolved in acetonitrile solvent. We discuss the influence of electrolyte concentration, chemical structure of the ionic salt, temperature, conducting versus semiconducting nature of the electrode, electrode geometry and surface roughness on the electric double layer structure and capacitance and compare these properties with those obtained for pure room temperature ionic liquids. We show that electrolytes consisting of solutions of ions can behave quite differently from pure ionic liquid electrolytes.
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Affiliation(s)
- Jenel Vatamanu
- University of Utah, MSE Department, Salt Lake City, UT 84112, USA
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Kiyohara K, Yamagata M, Ishikawa M. Electrochemical and structural properties of the electrical double layer of two-component electrolytes in response to varied electrode potential. J Chem Phys 2016; 144:134701. [DOI: 10.1063/1.4944927] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Affiliation(s)
- Kenji Kiyohara
- Inorganic Functional Material Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka 563-8577, Japan
| | - Masaki Yamagata
- Faculty of Chemistry, Materials and Bioengineering, Kansai University, 3-3-35 Yamate-cho, Suita, Osaka 564-8680, Japan
| | - Masashi Ishikawa
- Faculty of Chemistry, Materials and Bioengineering, Kansai University, 3-3-35 Yamate-cho, Suita, Osaka 564-8680, Japan
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Chu M, Miller M, Dutta P. Crowding and Anomalous Capacitance at an Electrode-Ionic Liquid Interface Observed Using Operando X-ray Scattering. ACS CENTRAL SCIENCE 2016; 2:175-80. [PMID: 27163044 PMCID: PMC4827468 DOI: 10.1021/acscentsci.6b00014] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2016] [Indexed: 05/02/2023]
Abstract
Room temperature ionic liquids are widely recognized as novel electrolytes with properties very different from those of aqueous solutions, and thus with many potential applications, but observing how they actually behave at electrolytic interfaces has proved to be challenging. We have studied the voltage-dependent structure of [TDTHP](+)[NTF2](-) near its interface with an electrode, using in situ synchrotron X-ray reflectivity. An anion-rich layer develops at the interface above a threshold voltage of +1.75 V, and the layer thickness increases rapidly with voltage, reaching ∼6 nm (much larger that the anion dimensions) at +2.64 V. These results provide direct confirmation of the theoretical prediction of "crowding" of ions near the interface. The interfacial layer is not purely anionic but a mixture of up to ∼80% anions and the rest cations. The static differential capacitance calculated from X-ray measurements shows an increase at higher voltages, consistent with a recent zero-frequency capacitance measurement but inconsistent with ac capacitance measurements.
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18
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Nishi N, Uruga T, Tanida H. Potential dependent structure of an ionic liquid at ionic liquid/water interface probed by x-ray reflectivity measurements. J Electroanal Chem (Lausanne) 2015. [DOI: 10.1016/j.jelechem.2015.11.004] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Abstract
Capacitive energy storage devices are receiving increasing experimental and theoretical attention due to their enormous potential for energy applications. Current research in this field is focused on the improvement of both the energy and the power density of supercapacitors by optimizing the nanostructure of porous electrodes and the chemical structure/composition of the electrolytes. However, the understanding of the underlying correlations and the mechanisms of electric double layer formation near charged surfaces and inside nanoporous electrodes is complicated by the complex interplay of several molecular scale phenomena. This Perspective presents several aspects regarding the experimental and theoretical research in the field, discusses the current atomistic and molecular scale understanding of the mechanisms of energy and charge storage, and provides a brief outlook to the future developments and applications of these devices.
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Affiliation(s)
- Jenel Vatamanu
- Department of Materials Science & Engineering, The University of Utah , 122 S. Central Campus Drive, Salt Lake City, Utah 84112, United States
| | - Dmitry Bedrov
- Department of Materials Science & Engineering, The University of Utah , 122 S. Central Campus Drive, Salt Lake City, Utah 84112, United States
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