Vladislav Ivaništšev

Restructuring of the electrical double layer in ionic liquids upon charging

We have investigated the electrical double layer (EDL) structure at an interface between ionic liquid (IL) and charged surface using molecular dynamics simulations. We show that for three different models of ILs the EDL restructuring, driven by surface charging, can be rationalized by the use of two parameters--renormalized surface charge (κ) and charge excess in the interfacial layers (λ). Analysis of the relationship between the λ and κ parameters provides new insights into mechanisms of over-screening and charge-driven structural transitions in the EDL in ionic liquids. We show that the restructuring of the EDL upon charging in all three studied systems has two characteristic regimes: (1) transition from the bulk-like (κ(Ion) = 0) to the multilayer structure (κ(Ion) ≈ 0.5) through the formation of an ionic bilayer of counter- and co-ions; and (2) transition from the multilayer (κ(Ion) ≈ 0.5) to the crowded (κ(Ion) > 1) structure through the formation of a monolayer of counter-ions at κ(Ion) = 1.

Molecular dynamics simulation of the behaviour of water in nano-confined ionic liquid-water mixtures.

This work describes the behaviour of water molecules in 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid under nanoconfinement, between graphene sheets. By means of molecular dynamics simulations, the adsorption of water molecules at the graphene surface is studied. A depletion of water molecules in the vicinity of the neutral and negatively charged graphene surfaces, and their adsorption at the positively charged surface are observed in line with the preferential hydration of the ionic liquid anions. The findings are appropriately described using a two-level statistical model. The confinement effect on the structure and dynamics of the mixtures is thoroughly analyzed using the density and the potential of mean force profiles, as well as by the vibrational densities of the states of water molecules near the graphene surface. The orientation of water molecules and the water-induced structural transitions in the layer closest to the graphene surface are also discussed.

Molecular origin of high free energy barriers for alkali metal ion transfer through ionic liquid–graphene electrode interfaces

In this work we study mechanisms of solvent-mediated ion interactions with charged surfaces in ionic liquids by molecular dynamics simulations, in an attempt to reveal the main trends that determine ion-electrode interactions in ionic liquids. We compare the interfacial behaviour of Li(+) and K(+) at a charged graphene sheet in a room temperature ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate, and its mixtures with lithium and potassium tetrafluoroborate salts. Our results show that there are dense interfacial solvation structures in these electrolytes that lead to the formation of high free energy barriers for these alkali metal cations between the bulk and direct contact with the negatively charged surface. We show that the stronger solvation of Li(+) in the ionic liquid leads to the formation of significantly higher interfacial free energy barriers for Li(+) than for K(+). The high free energy barriers observed in our simulations can explain the generally high interfacial resistance in electrochemical storage devices that use ionic liquid-based electrolytes. Overcoming these barriers is the rate-limiting step in the interfacial transport of alkali metal ions and, hence, appears to be a major drawback for a generalised application of ionic liquids in electrochemistry. Some plausible strategies for future theoretical and experimental work for tuning them are suggested.

Predictions of Physicochemical Properties of Ionic Liquids with DFT

Nowadays, density functional theory (DFT)-based high-throughput computational approach is becoming more efficient and, thus, attractive for finding advanced materials for electrochemical applications. In this work, we illustrate how theoretical models, computational methods, and informatics techniques can be put together to form a simple DFT-based throughput computational workflow for predicting physicochemical properties of room-temperature ionic liquids. The developed workflow has been used for screening a set of 48 ionic pairs and for analyzing the gathered data. The predicted relative electrochemical stabilities, ionic charges and dynamic properties of the investigated ionic liquids are discussed in the light of their potential practical applications.

Direct migration of scientific computing experiments to the cloud

Scientific computing applications usually need huge amounts of computational power. The cloud provides interesting high-performance computing solutions, with its promise of virtually infinite resources. However, migrating scientific computing problems to clouds and the re-creation of a software environment on the vendor-supplied OS and cloud instances is often a laborious task. It is also assumed that the scientist who is performing the experiments has significant knowledge of computer science, cloud computing and the migration procedure. Most often, this is not the case. Considering this obstacle, we have designed a tool that helps scientists to migrate their applications to the cloud. The idea is to migrate the complete software environment, in which the scientists have set up their experiments, directly to the cloud. The developed desktop-to-cloud-migration (D2CM) tool supports transformation and migration of virtual machine images, deployment description and life-cycle management for applications to be hosted on Amazons Elastic Cloud Computing (EC2) or compatible infrastructure such as Eucalyptus. The paper also presents an electrochemical case study which extensively used the tool in drawing domain specific results. From the analysis, it was observed that D2CM tool not only helps in the migration process and simplifying the work of the scientist, but also helps in optimizing the calculations, compute clusters and thus the costs for conducting scientific computing experiments on the cloud.

Density Functional Theory Study of Ionic Liquid Adsorption on Circumcoronene Shaped Graphene

Carbon materials have a range of properties such as high electrical conductivity, high specific surface area, and mechanical flexibility are relevant for electrochemical applications. Carbon materials are utilised in energy conversion-and-storage devices along with electrolytes of complementary properties. In this work, we study the interaction of highly concentrated electrolytes (ionic liquids) at a model carbon surface (circumcoronene) using density functional theory methods. Our results indicate the decisive role of the dispersion interactions that noticeably strengthen the circumcoronene-ion interaction. Also, we focus on the adsorption of halide anions as the electrolytes containing these ions are promising for practical use in supercapacitors and solar cells.

Performance of SCAN density functional for a set of ionic liquid ion pairs

Computational chemistry is a powerful tool for the discovery of novel materials. In particular, it is used to simulate ionic liquids in search of electrolytes for electrochemical applications. Herein, the choice of the computational method is not trivial, as it has to be both efficient and accurate. Density functional theory (DFT) methods with appropriate corrections for the systematic weaknesses can give precision close to that of the post-Hartree--Fock coupled cluster methods with a fraction of their cost. Thence, we have evaluated the performance of a recently developed non-empirical Strongly Constrained and Appropriately Normed (SCAN) density functional on electronic structure calculations of ionic liquid ion pairs. The performance of SCAN and other popular functionals (PBE, M06-L, B2PLYP) among with Grimmes dispersion correction and Boys-Bernardi basis set superposition error correction was compared to DLPNO-CCSD(T)/CBS. We show that SCAN reproduces coupled-cluster results for describing the employed dataset of 48 ion pairs.

Ionic liquids at interfaces: general discussion

Andrew Abbott, Matthew Addicoat, Leigh Aldous, Radha Gobinda Bhuin, Natalia Borisenko, José Nuno Canongia Lopes, Ryan Clark, Samuel Coles, Margarida Costa Gomes, Benjamin Cross, Jeffrey Everts, Millicent Firestone, Ramesh Gardas, Matthieu Gras, Simon Halstead, Christopher Hardacre, John Holbrey, Toshiyuki Itoh, Vladislav Ivaništšev, Johan Jacquemin, Philip Jessop, Robert Jones, Barbara Kirchner, Sichao Li, Ruth Lynden-Bell, Doug MacFarlane, Florian Maier, Markus Mezger, Aǵılio Pádua, Octavian D. Pavel, Susan Perkin, Simon Purcell, Mark Rutland, John M. Slattery, Sefik Suzer, Kazuhisa Tamura, Morgan L. Thomas, Shraeddha Tiwari, Seiji Tsuzuki, Betul Uralcan, William Wallace, Masayoshi Watanabe and James Wishart