Effects of Dielectric Saturation upon the Diffuse Double Layer and the Free Energy of Hydration of Ions

Grahame, David C.

doi:10.1063/1.1747807

Cited by 193 publications

(75 citation statements)

References 3 publications

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“…The classical effect of dielectric saturation reduces the permittivity at large fields due to the alignment of solvent dipoles [32,[37][38][39], although an increase in dipole density near a surface may have the opposite effect [40]. A recent model which included excess ion polarizability demonstrated excellent agreement with experimental capacitance data on surfaces with no adsorption [17].…”

Section: B Modifications For Chemical Effectssupporting

confidence: 54%

Effects of electrostatic correlations on electrokinetic phenomena

2012

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The classical theory of electrokinetic phenomena is based on the mean-field approximation, that the electric field acting on an individual ion is self-consistently determined by the local mean charge density. This paper considers situations, such as concentrated electrolytes, multivalent electrolytes, or solvent-free ionic liquids, where the mean-field approximation breaks down. A fourth-order modified Poisson equation is developed that captures the essential features in a simple continuum framework. The model is derived as a gradient approximation for non-local electrostatics of interacting effective charges, where the permittivity becomes a differential operator, scaled by a correlation length. The theory is able to capture subtle aspects of molecular simulations and allows for simple calculations of electrokinetic flows in correlated ionic fluids, for the first time. Charge-density oscillations tend to reduce electro-osmotic flow and streaming current, and over-screening of surface charge can lead to flow reversal. These effects also help to explain the suppression of induced-charge electrokinetic phenomena at high salt concentations.

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Section: B Modifications For Chemical Effectssupporting

confidence: 54%

Effects of electrostatic correlations on electrokinetic phenomena

2012

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“…surface (within a few angstroms), taking values as low as five near the Stern plane (Grahame, 1950). It would, perhaps, be more correct to use a smaller value of ε r that would take into account the reduction of the permittivity in the diffuse layer, which would give larger values of calculated zeta potential at high salinity, and which seem to be supported by recent experimental determinations (Jaafar et al, 2009).…”

Section: Pore Fluid Relative Electric Permittivitymentioning

confidence: 51%

Streaming-potential coefficient of reservoir rock: A theoretical model

2012

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The streaming potential is that electrical potential which develops when an ionic fluid flows through the pores of a rock. It is an old concept that is recently being applied in many fields from monitoring water fronts in oil reservoirs to understanding the mechanisms behind synthetic earthquakes. We have carried out fundamental theoretical modeling of the streaming-potential coefficient as a function of pore fluid salinity, pH, and temperature by modifying the HS equation for use with porous rocks and using input parameters from established fundamental theory (the Debye screening length, the Stern-plane potential, the zeta potential, and the surface conductance). The model also requires the density, electrical conductivity, relative electric permittivity and dynamic viscosity of the bulk fluid, for which empirical models are used so that the temperature of the model may be varied. These parameters are then combined with parameters that describe the rock microstructure. The resulting theoretical values have been compared with a compilation of data for siliceous materials comprising 290 streaming-potential coefficient measurements and 269 zeta-potential measurements obtained experimentally for 17 matrix-fluid combinations (e.g., sandstone saturated with KCl), using data from 29 publications. The theoretical model was found to ably describe the main features of the data, whether taken together or on a sample by sample basis. The low-salinity regime was found to be controlled by surface conduction and rock microstructure, and was sensitive to changes in porosity, cementation exponent, formation factor, grain size, pore size and pore throat size as well as specific surface conductivity. The high-salinity regime was found to be subject to a zeta-potential offset that allows the streaming-potential coefficient to remain significant even as the saturation limit is approached.

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“…Other models for r (E) were reported in Ref. [133][134][135][136][137][138][139][140][141][142][143]. Table I summarizes the values of r (0), n, and β associated with the Booth model for common electrolyte solvents namely water, propylene carbonate (PC), and acetonitrile (AN).…”

Section: Equilibrium Modelingmentioning

confidence: 99%

Recent Advances in Continuum Modeling of Interfacial and Transport Phenomena in Electric Double Layer Capacitors

Pilon

Wang

d’Entremont

2015

J. Electrochem. Soc.

117

105

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This paper reviews recent advances in physical modeling of interfacial and transport phenomena in electric double layer capacitors (EDLCs) under both equilibrium and dynamic cycling. The models are based on continuum theory and account for (i) the Stern layer at the electrode/electrolyte interface, (ii) finite ion sizes, (iii) steric repulsions, (iv) asymmetric electrolytes featuring ions with different valencies, effective diameters, or diffusion coefficients, (v) electric-field-dependent dielectric permittivity of the electrolyte, and/or (vi) porous three-dimensional morphology of the electrodes. Typical characterization methods such as electrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic cycling were reproduced numerically to identify the dominant physical phenomena and to gain insight into experimental observations. In addition, recent thermal models derived from first principles for EDLCs under constant-current cycling accounting for irreversible Joule heating and reversible heat generation rates due to ion diffusion, steric effects, and changes in entropy are discussed. Scaling analyses of both equilibrium and dynamic models are also presented as a way to identify self-similar and asymptotic behaviors as well as to develop design rules for electrodes and electrolytes of next generation EDLCs. Electrical double layer capacitors (EDLCs) store energy by ion adsorption in the electrical double layer (EDL) forming at the electrode/electrolyte interfaces.1,2 This process is highly reversible and the cycle life of EDLCs exceeds 100,000 cycles.2,3 EDLCs can operate in a wide range of specific energy and power densities. This versatility is a key feature for electrical energy storage, energy harvesting, and energy regeneration applications. 2The performance of EDLCs is determined by the combination of the electrode material and morphology and of the electrolyte. In general, the key attributes of a good electrode include 1,3-7 (i) large surface area accessible to ions to maximize charge storage, (ii) optimum pore size, short pore length, and good pore connectivity to facilitate ion transport, (iii) large electrical conductivity to enable fast charging and discharging and low ohmic resistance, (iv) thin electrodes and current collectors to reduce the total resistance of the device, (v) small leakage current, (vi) small self-discharge, (vii) environmentally friendly materials, and (viii) low price. However, satisfying all these criteria simultaneously is challenging. For example, increasing surface area often results in larger electrode electrical resistivity.1 Micropores with diameter less than 2 nm contribute greatly to EDLCs capacitance.2 But pores smaller than the ion size are typically inactive and do not contribute to charge storage. 1,8 Porous electrodes must also be electrochemically accessible to ions. Then, interconnected mesopores with diameter ranging from 2 to 50 nm are necessary for fast charging thanks to their easier accessibility to ions. 1,6,[9][10][11] In practice, electrode...

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Effects of Dielectric Saturation upon the Diffuse Double Layer and the Free Energy of Hydration of Ions

Cited by 193 publications

References 3 publications

Effects of electrostatic correlations on electrokinetic phenomena

Effects of electrostatic correlations on electrokinetic phenomena

Streaming-potential coefficient of reservoir rock: A theoretical model

Recent Advances in Continuum Modeling of Interfacial and Transport Phenomena in Electric Double Layer Capacitors

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