Ionic Layering and Overcharging in Electrical Double Layers in a Poisson-Boltzmann Model

Gupta, A and Govind Rajan, A and Carter, EA and Stone, HA (2020) Ionic Layering and Overcharging in Electrical Double Layers in a Poisson-Boltzmann Model. In: Physical Review Letters, 125 (18).

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Abstract

Electrical double layers (EDLs) play a significant role in a broad range of physical phenomena related to colloidal stability, diffuse-charge dynamics, electrokinetics, and energy storage applications. Recently, it has been suggested that for large ion sizes or multivalent electrolytes, ions can arrange in a layered structure inside the EDLs. However, the widely used Poisson-Boltzmann models for EDLs are unable to capture the details of ion concentration oscillations and the effect of electrolyte valence on such oscillations. Here, by treating a pair of ions as hard spheres below the distance of closest approach and as point charges otherwise, we are able to predict ionic layering without any additional parameters or boundary conditions while still being compatible with the Poisson-Boltzmann framework. Depending on the combination of ion valence, size, and concentration, our model reveals a structured EDL with spatially oscillating ion concentrations. We report the dependence of critical ion concentration, i.e., the ion concentration above which the oscillations are observed, on the counter-ion valence and the ion size. More importantly, our model displays quantitative agreement with the results of computationally intensive models of the EDL. Finally, we analyze the nonequilibrium problem of EDL charging and demonstrate that ionic layering increases the total charge storage capacity and the charging timescale. © 2020 American Physical Society.

Item Type:	Journal Article
Publication:	Physical Review Letters
Publisher:	American Physical Society
Additional Information:	The copyright for this belongs to American Physical Society.
Keywords:	Concentration (process); Electrohydrodynamics; Electrolytes; Electromagnetic fields; Energy storage, Colloidal Stability; Electrical double layers; Energy storage applications; Ion concentrations; Layered Structures; Nonequilibrium problems; Physical phenomena; Quantitative agreement, Ions
Department/Centre:	Division of Mechanical Sciences > Chemical Engineering
Date Deposited:	24 Dec 2021 07:21
Last Modified:	24 Dec 2021 07:21
URI:	http://eprints.iisc.ac.in/id/eprint/67346

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