Double-Edged Sword of Ion-Size Asymmetry in Energy Storage of Supercapacitors

Qing, Leying; Jiang, Jian

doi:10.1021/acs.jpclett.1c03900

Cited by 12 publications

(10 citation statements)

References 62 publications

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“…As mentioned above, thermodynamic nonideality can be readily incorporated into the PNP equations. With the local excess chemical represented by one of the equilibrium models for inhomogeneous ionic systems, the MPNP equations (viz., TDDFT) can be used to examine the charging dynamics at large surface potentials and finite electrolyte concentrations. − …”

Section: Dynamics Of Edl Chargingmentioning

confidence: 99%

Understanding the Electric Double-Layer Structure, Capacitance, and Charging Dynamics

2022

Chem. Rev.

354

197

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Significant progress has been made in recent years in theoretical modeling of the electric double layer (EDL), a key concept in electrochemistry important for energy storage, electrocatalysis, and multitudes of other technological applications. However, major challenges remain in understanding the microscopic details of the electrochemical interface and charging mechanisms under realistic conditions. This review delves into theoretical methods to describe the equilibrium and dynamic responses of the EDL structure and capacitance for electrochemical systems commonly deployed for capacitive energy storage. Special emphasis is given to recent advances that intend to capture the nonclassical EDL behavior such as oscillatory ion distributions, polarization of nonmetallic electrodes, charge transfer, and various forms of phase transitions in the micropores of electrodes interfacing with an organic electrolyte or ionic liquid. This comprehensive analysis highlights theoretical insights into predictable relationships between materials characteristics and electrochemical performance and offers a perspective on opportunities for further development toward rational design and optimization of electrochemical systems.

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Section: Dynamics Of Edl Chargingmentioning

confidence: 99%

Understanding the Electric Double-Layer Structure, Capacitance, and Charging Dynamics

2022

Chem. Rev.

354

197

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“…The above decomposition scheme, following ref , is expressed as Within a continuum picture, Δϕ free is written as where the first term denotes the potential change over the diffuse layer, which is derived from the Bikerman model considering finite ion size, , is the Debye length, ϵ b is the dielectric permittivity of the bulk solution, c b is the bulk ion concentration, R is the gas constant, F is the Faraday constant, T is the temperature, and γ = 2 c b d h 3 with d h being the diameter of hydrated ions. Size asymmetry of cations and anions is not considered here, for the sake of an analytical expression of Δϕ free as a function of σ free , and effects of size asymmetry on the C dl are known already. − …”

Section: Theoretical Methodsmentioning

confidence: 99%

Zooming into the Inner Helmholtz Plane of Pt(111)–Aqueous Solution Interfaces: Chemisorbed Water and Partially Charged Ions

Huang

2023

JACS Au

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The double layer on transition metals, i.e., platinum, features chemical metal–solvent interactions and partially charged chemisorbed ions. Chemically adsorbed solvent molecules and ions are situated closer to the metal surface than electrostatically adsorbed ions. This effect is described tersely by the concept of an inner Helmholtz plane (IHP) in classical double layer models. The IHP concept is extended here in three aspects. First, a refined statistical treatment of solvent (water) molecules considers a continuous spectrum of orientational polarizable states, rather than a few representative states, and non-electrostatic, chemical metal–solvent interactions. Second, chemisorbed ions are partially charged, rather than being electroneutral or having integral charges as in the solution bulk, with the coverage determined by a generalized, energetically distributed adsorption isotherm. The surface dipole moment induced by partially charged, chemisorbed ions is considered. Third, considering different locations and properties of chemisorbed ions and solvent molecules, the IHP is divided into two planes, namely, an AIP (adsorbed ion plane) and ASP (adsorbed solvent plane). The model is used to study how the partially charged AIP and polarizable ASP lead to intriguing double-layer capacitance curves that are different from what the conventional Gouy–Chapman–Stern model describes. The model provides an alternative interpretation for recent capacitance data of Pt(111)–aqueous solution interfaces calculated from cyclic voltammetry. This revisit brings forth questions regarding the existence of a pure double-layer region at realistic Pt(111). The implications, limitations, and possible experimental confirmation of the present model are discussed.

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“…Being computationally inexpensive (compared to simulations) and accounting for ion sizes and some correlations, static and dynamic DFTs have become a popular tool to study various phenomena in confined ionic liquids, from anomalous capacitance increase and solvent effects − to charging dynamics − and temperature effects. ,, In this section, we briefly describe the main phenomena studied with DFT. We refer the interested readers to a review by Härtel, which covers the application of DFT to confined ILs before 2017, with a particular focus on technicalities.…”

Section: Classical Density Functional Theorymentioning

confidence: 99%

Theory and Simulations of Ionic Liquids in Nanoconfinement

et al. 2023

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Room-temperature ionic liquids (RTILs) have exciting properties such as nonvolatility, large electrochemical windows, and remarkable variety, drawing much interest in energy storage, gating, electrocatalysis, tunable lubrication, and other applications. Confined RTILs appear in various situations, for instance, in pores of nanostructured electrodes of supercapacitors and batteries, as such electrodes increase the contact area with RTILs and enhance the total capacitance and stored energy, between crossed cylinders in surface force balance experiments, between a tip and a sample in atomic force microscopy, and between sliding surfaces in tribology experiments, where RTILs act as lubricants. The properties and functioning of RTILs in confinement, especially nanoconfinement, result in fascinating structural and dynamic phenomena, including layering, overscreening and crowding, nanoscale capillary freezing, quantized and electrotunable friction, and superionic state. This review offers a comprehensive analysis of the fundamental physical phenomena controlling the properties of such systems and the current state-of-the-art theoretical and simulation approaches developed for their description. We discuss these approaches sequentially by increasing atomistic complexity, paying particular attention to new physical phenomena emerging in nanoscale confinement. This review covers theoretical models, most of which are based on mapping the problems on pertinent statistical mechanics models with exact analytical solutions, allowing systematic analysis and new physical insights to develop more easily. We also describe a classical density functional theory, which offers a reliable and computationally inexpensive tool to account for some microscopic details and correlations that simplified models often fail to consider. Molecular simulations play a vital role in studying confined ionic liquids, enabling deep microscopic insights otherwise unavailable to researchers. We describe the basics of various simulation approaches and discuss their challenges and applicability to specific problems, focusing on RTIL structure in cylindrical and slit confinement and how it relates to friction and capacitive and dynamic properties of confined ions.

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Double-Edged Sword of Ion-Size Asymmetry in Energy Storage of Supercapacitors

Cited by 12 publications

References 62 publications

Understanding the Electric Double-Layer Structure, Capacitance, and Charging Dynamics

Understanding the Electric Double-Layer Structure, Capacitance, and Charging Dynamics

Zooming into the Inner Helmholtz Plane of Pt(111)–Aqueous Solution Interfaces: Chemisorbed Water and Partially Charged Ions

Theory and Simulations of Ionic Liquids in Nanoconfinement

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