Project

Electric double layer

Goal: Atomic modeling of the electric double layer using static bilayer configurations, implicit solvent methods, and ab initio molecular dynamics simulations and establishing concrete understandings of the double layer based on the model electrolyte/electrode interfaces.

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Project log

Sung Sakong
added a research item
This article reviews recent forays in theoretical modeling of the double layer structure at electrode/electrolyte interfaces by current atomistic and continuum approaches. We will briefly discuss progress in both approaches and present a perspective on how to better describe the electric double layer by combining the unique advantages of each method. First-principles atomistic approaches provide the most detailed insights into the electronic and geometric structure of electrode/electrolyte interfaces. However, they are numerically too demanding to allow for a systematic investigation of the electric double layers over a wide range of electrochemical conditions. Yet, they can provide valuable input for continuum approaches that can capture the influence of the electrochemical environment on a larger length and time scale due to their numerical efficiency. However, continuum approaches rely on reliable input parameters. Conversely, continuum methods can provide a preselection of interface structures and conditions to be further studied on the atomistic level.
Sung Sakong
added a research item
Structures and processes at water/metal interfaces play an important technological role in electrochemical energy conversion and storage, photoconversion, sensors, and corrosion, just to name a few. However, they are also of fundamental significance as a model system for the study of solid−liquid interfaces, which requires combining concepts from the chemistry and physics of crystalline materials and liquids. Particularly interesting is the fact that the water−water and water−metal interactions are of similar strength so that the structures at water/metal interfaces result from a competition between these comparable interactions. Because water is a polar molecule and water and metal surfaces are both polarizable, explicit consideration of the electronic degrees of freedom at water/metal interfaces is mandatory. In principle, ab initio molecular dynamics simulations are thus the method of choice to model water/metal interfaces, but they are computationally still rather demanding. Here, ab initio simulations of water/metal interfaces will be reviewed, starting from static systems such as the adsorption of single water molecules, water clusters, and icelike layers, followed by the properties of liquid water layers at metal surfaces. Technical issues such as the appropriate first-principles description of the water−water and water−metal interactions will be discussed, and electrochemical aspects will be addressed. Finally, more approximate but numerically less demanding approaches to treat water at metal surfaces from first-principles will be briefly discussed.
Sung Sakong
added a research item
The theoretical modeling of the double layer structure at electrode/electrolyte interfaces by current atomistic and continuum approaches is reviewed. We will briefly discuss recent progress in both approaches and present a perspective on how to better describe the electric double layer by exchanging the unique advantages of each method. First-principles atomistic approaches provide detailed insights into the electronic and geometric structure of electrode/electrolyte interfaces. However, they are numerically too demanding to allow a systematic study of the properties of electric double layers for a wide range of electrochemical conditions. Still they can provide valuable input for continuum approaches which due to their numerical efficiency can capture the influence of the electrochemical environment on larger length and time scale. Still, these methods rely on reliable input parameters. Conversely, continuum methods can provide a preselection of interface structures and conditions to be further studied on the atomistic level.
Sung Sakong
added a research item
Structures and processes at water/metal interfaces play an important technological role in electro-chemical energy conversion and storage, photoconversion, sensors or corrosion, just to name a few. However, they are also of fundamental significance as a model system for the study of solid-liquid interfaces which requires to combine concepts from chemistry and physics of crystalline materials and of liquids. Particularly interesting is the fact that the water-water and the water-metal interaction are of similar strength so that the structures at water/metal interfaces result from a competition between these comparable interactions. As water is a polar molecule and water and metal surfaces are both polarizable, furthermore the explicit consideration of the electronic degrees of freedom at water/metal interfaces is mandatory. In principle, ab initio molecular dynamics simulations are thus the method of choice to model water/metal interfaces, but they are computationally still rather demanding. Here, ab initio simulations of water/metal interfaces will be reviewed, starting from static systems such as the adsorption of single water molecules, water clusters and ice-like layers, followed by the properties of liquid water layers at metal surfaces. Technical issues such as the appropriate first-principles description of the water-water and the water-metal interaction will be discussed, also electrochemical aspects will addressed. Finally, more approximate, but numerically less demanding approaches to treat water at metal surfaces from first principles will be briefly discussed.
Axel Gross
added a research item
Semi-tutorial talk about theoretical methods to describe electrode/electrolyte interfaces
Sung Sakong
added a research item
We have performed density functional theory calculations to explore the possibility to overcome the linear scaling relations in the oxygen reduction reaction (ORR) using local inhomogeneities on Pt-based surface alloys, supported Pt monolayers, and Pt islands. We demonstrate that invoking inequivalent neighboring reaction sites allows overcoming the restrictions of one-dimensional linear scaling relations. As a consequence, the ORR activity at a (111) edge site of a Pt island on a Ru(0001) substrate outperforms the one on flat Pt(111). Furthermore, we show that it is critical to appropriately take the electrochemical environment into account, including the proper surface coverage and the presence of the electrolyte, which leads to microscopically modified ORR reaction schemes and a redetermination of the rate-limiting step.
Sung Sakong
added a project goal
Atomic modeling of the electric double layer using static bilayer configurations, implicit solvent methods, and ab initio molecular dynamics simulations and establishing concrete understandings of the double layer based on the model electrolyte/electrode interfaces.
 
Sung Sakong
added a research item
A structural analysis of solvating water layers on a Pt(111) electrode has been performed based on extensive ab initio molecular dynamics simulations. We have emulated different electrochemical conditions by varying...
Sung Sakong
added a research item
The influence of steps and island edges on the local electronic structure of a (bi-)metallic single crystalline electrode surface and on the local, site-specific adsorption energy of adsorbed species, the so-called structural effects, was studied by periodic density functional theory based calculations, focusing on longer-range effects. Using hydrogen adsorption energies as a local probe, calculations were performed both for partly Pt monolayer covered planar Ru(0001) surfaces and for a stepped Ru(1019\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$10\bar {19}$\end{document}) surface decorated with a row of Pt atoms. The calculations demonstrate that the steps/island edges affect not only the nearest neighbor adsorption sites but also more distant ones with the extent depending on the particular structure. This longer-range effect is in excellent agreement with recent temperature-programmed desorption and spectroscopy experiments (Hartmann et al. Phys. Chem. Chem. Phys. 14, 10919, 2012). For the interaction of water molecules with partly Pt monolayer covered Ru(0001), similar trends as in the hydrogen adsorption have been found. In addition, hydrogen adsorption energies as a function of coverage have been used to derive the hydrogen coverage as a function of the electrode potential, exhibiting a broad range of stable hydrogen adsorption structures. Graphical AbstractLocal adsorption properties of Pt monolayer island modified Ru(0001) electrodes are studied by first-principles calculations
Sung Sakong
added a research item
The description of electrode–electrolyte interfaces is based on the notion of the formation of an electric double layer (EDL). Most of the concepts underlying its structure and properties have been developed more than one hundred years ago based on continuum approaches. Still, a complete atomistic theoretical description is missing. Here, first the traditional models of the EDL will be briefly reviewed before recent atomistic first-principles approaches using either explicit aqueous electrolytes or a grand-canonical formalism will be presented. Finally, the importance of the formation of an EDL at electrode/electrolyte interfaces in batteries will be discussed.
Sung Sakong
added 4 research items
We present a computational study of the interface of a Pt electrode and an aqueous electrolyte employing semi-empirical dispersion corrections and an implicit solvent model within first-principles calculations. The electrode potential is parametrized within the computational hydrogen electrode scheme. Using one explicit layer, we find that the most realistic interface configuration is a water bilayer in the H-up configuration. Furthermore, we focus on the contribution of the dispersion interaction and the presence of water on H, O, and OH adsorption energies. This study demonstrates that the implicit water scheme represents a computationally efficient method to take the presence of an aqueous electrolyte interface with a metal electrode into account.
The electro-oxidation of methanol on Pt(111) is studied based on periodic density functional theory calculations. The aqueous electrolyte is taken into account using an implicit solvent model, and the dependence of the reaction energetics on the electrode potential is derived using the concept of the computational hydrogen electrode. The total oxidation of methanol becomes thermodynamically preferred at electrode potentials above U = 0.6 V relative to the standard hydrogen electrode. We propose a most favorable reaction path involving surface carboxyl as the last reaction intermediate before CO2 formation, which can either be formed in a indirect mechanism from adsorbed CO or in a direct mechanism from formic acid. The presence of the aqueous electrolyte significantly stabilizes reaction intermediates that contain hydrophilic groups. This also leads to a selectivity for the initial C-H bond breaking process with respect to the initial O-H bond breaking of methanol that is increased by 3 orders of magnitude at room temperature when solvent effects are considered.
The structure of a liquidwater layer on Pt(111) has been studied by ab initiomolecular dynamics simulations based on periodic density functional theory calculations. First the reliability of the chosen exchange-correlation function has been validated by considering water clusters, bulk icestructures, and bulk liquidwater, confirming that the dispersion corrected RPBE-D3/zero functional is a suitable choice. The simulations at room temperature yield that a water layer that is six layers thick is sufficient to yield liquidwater properties in the interior of the water film. Performing a statistical average along the trajectory, a mean work function of 5.01 V is derived, giving a potential of zero charge of Pt(111) of 0.57 V vs. standard hydrogen electrode, in good agreement with experiments. Therefore we propose the RPBE-D3/zero functional as the appropriate choice for first-principles calculations addressing electrochemical aqueous electrolyte/metal electrodeinterfaces.