Electrical Double Layers: Theory and Simulations

Schmickler, Wolfgang

doi:10.1002/9783527610426.bard010202

Cited by 4 publications

(2 citation statements)

References 73 publications

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“…Currently, there is no such uniform atomistic methodology for the electrode potentials in a range of ±1 V around the OCP since it would have to cover the processes whose characteristic times range from attoseconds (electron transfer (ET) time) to hundreds of picoseconds (solvent dielectric relaxation) at length scales ranging from angstroms to tens of nanometers. Instead, we currently have methodologies that either elaborate the structure of the classical EDL [1][2][3] or study the charge transfer per se assuming consistency between the atomistic structure of the EDL and the external conditions. 4 The crossover between the two approaches is not well defined, such * Electrochemical Society Member.…”

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confidence: 99%

Improving Continuum Models to Define Practical Limits for Molecular Models of Electrified Interfaces

Baskin

2017

J. Electrochem. Soc.

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We develop a continuum theory of electrolyte solutions in contact with a metal electrode, based on a generalized free energy functional, and use it to explore the structure of the electric double layer at different electrochemical conditions. The model captures the effects of specific adsorption of ions and solvent polarization, and can be applied on the same footing to cases with non-zero faradaic current, beyond the classical double-layer regime. These advances permit the prediction of peculiar character in the ion profiles at electrode potentials near the redox level, exploration of the electrochemical stability of the interface, and differentiation between the mechanisms of electron and ion transport and associated time scales. The developed methodology enables us to selfconsistently determine the fundamental limits for a microscopic description of biased interfaces, in terms characteristic sizes and time scales of relevant processes, within atomistic and ab initio molecular dynamics simulations. As the efficiency of electrochemical conversion is dictated by the energetics of elementary charge transfer reactions occurring at the electrode/electrolyte interface, the formulation of methods of control over these reactions has become the pivotal goal of fundamental material science for advanced energy storage systems. The ultimate goal of theoretical electrochemistry then is to explore the energetics of the relevant processes from an atomistic perspective by means of ab initio molecular dynamics (AIMD) where ionic and electronic components of the system are described explicitly and are constrained by various realistic conditions, such as the external bias, the temperature and the electrolyte concentration. However, despite more than a decade of efforts this goal is still far from being fulfilled.There are several interconnected fundamental problems to resolve before an atomistic approach could be routinely used to describe electrochemistry, if only at the level of a half-cell (i.e., a single electrodeelectrolyte interface). First, there are at least three distinct regimes of performance of the electrochemical interface and each of these is characterized by different sets of the time and space scales: a) the classical electric double layer (EDL) regime when no charge transfer is assumed, b) the regime of an electrode at equilibrium with the electrolyte (open circuit conditions, (OCP)) when only an exchange current in a form of mutually compensating fluxes of charged particles is possible, and c) the "true" electrochemical regime with a non-zero net faradaic current. As long as the goal of atomistic simulations is to reach a state when one would observe the actual electrochemical reactions driven by the bias, the computational electrode potential scanning protocol should carry the system through a set of (quasi-)equilibrium points at which the atomistic structure is consistent with the targeted external conditions. The key requirement for such simulations is thus thermodynamic stability of the interface that encom...

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confidence: 99%

Improving Continuum Models to Define Practical Limits for Molecular Models of Electrified Interfaces

Baskin

2017

J. Electrochem. Soc.

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“…We reiterate that the attention to the interplay of the molecular nature of the solvent and the statistical mechanics of the ion distribution in the electrical double layer is experiencing a renaissance nowadays, , but the problem per se is not new. We refer the reader to a detailed review of related effects in the monographic chapters in refs and , in particular to the section 2.1.10 devoted to this issue. Already then it was clear based on the results of molecular simulations that simple pictures of the ionic distributions near the charged electrodes are very much different from the standard double layer theories of the Gouy–Chapman type and its primitive solvent model extensions.…”

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confidence: 99%

The Dramatic Effect of Water Structure on Hydration Forces and the Electrical Double Layer

2023

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Forces between hydrophilic surfaces mediated by water are important in various systems from lipid membranes and solid surfaces to colloids and macromolecules, first discovered as a significant addition to DLVO forces at the nanoscale. These “hydration forces” have been studied in great detail experimentally using osmotic stress measurements, surface force apparatus, and AFM, and they have also been the subject of multiple theories and simulations. One spectacular feature observed in experimental and simulation studies was the nonmonotonic, oscillatory decay in the forces between atomically smooth surfaces. Forces between “rougher” surfaces exhibit only quasi-exponential, monotonic decay. Here we revisit this hydration force problem by exploring the consequences of an extended phenomenological Landau–Ginzburg approach that describes nonlocal correlations in water, linking them with the key features of the wave-number k-dependent nonlocal dielectric function of water. With corresponding boundary conditions, this theory predicts the observed oscillatory decay in hydration force between ideally flat surfaces, the oscillatory mode disappearing with just a tiny roughness of the surfaces (of mean height ca. of the size of a water molecule). This study also brings an important side message. Explanation of these observations appears only possible under an assumption of two modes of polarization in water, consistent with the behavior of the response function, i.e., Lorentzian at small k and resonance-like at higher k. This resolves the “force oscillation–non-oscillation” paradigm, which is a strong, although indirect indication of the existence of these two modes. We also consider other important subjects, such as how the distribution of ions near a charged surface reacts to the propensity for overscreening oscillations due to polarized water. This is important not only for the interactions between charged surfaces but also for the fundamental understanding of the structure of the electrical double layer at electrochemical interfaces. We show that even in dilute electrolytes, the distribution of ions in the vicinity of the polarized interface follows, although not literally, preferential positions corresponding to the potential wells caused by “resonance” water layering. For a sharp interface, the theory predicts that the decaying spatial oscillation profiles extend over a 1 to 2 nm distance from the interface. With the smearing of the interface and the corresponding suppression of the resonance water layering, oscillations in the spatial distribution of ions subside, resulting in a familiar Gouy–Chapman–Stern picture. At longer distances from the interface, whether smeared or not, the ion distribution profiles become Gouy–Chapman-like. The effect of the boundary conditions on water polarization at the interface goes beyond a trivial shift of the potential of zero charge. We show that they can dramatically affect the ion distribution near the charged surface. Last, but not least, we study how the interfacial water layerin...

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Specific Features of the Excitation of Surface Plasmons at the Interface between Metal and Aqueous Solution of Extremely Low Concentration

2020

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Electrical Double Layers: Theory and Simulations

Abstract: The sections in this article are Introduction Gouy–Chapman Theory and its Extensions Theoretical Methods and Principles of Computer Simulations Integral Equations Computer Simulations Monte Carlo simulations Molecular Dynamics Car–Par… Show more

Cited by 4 publications

References 73 publications

Improving Continuum Models to Define Practical Limits for Molecular Models of Electrified Interfaces

Improving Continuum Models to Define Practical Limits for Molecular Models of Electrified Interfaces

The Dramatic Effect of Water Structure on Hydration Forces and the Electrical Double Layer

Specific Features of the Excitation of Surface Plasmons at the Interface between Metal and Aqueous Solution of Extremely Low Concentration

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