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Gibson LD, Roy S, Khanal R, Chahal R, Sedova A, Bryantsev VS. Tracing mechanistic pathways and reaction kinetics toward equilibrium in reactive molten salts. Chem Sci 2024; 15:3116-3129. [PMID: 38425531 PMCID: PMC10901494 DOI: 10.1039/d3sc06587a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2023] [Accepted: 01/17/2024] [Indexed: 03/02/2024] Open
Abstract
In the dynamic environment of multi-component reactive molten salts, speciation unfolds as a complex process, involving multiple competing reaction pathways that are likely to face free energy barriers before reaching the reaction equilibria. Herein, we unravel intricate speciation in the AlCl3-KCl melt compositions with rate theory and ab initio molecular dynamics simulations. We find that the compositions with 100 and 50 mol% AlCl3 exclusively comprise neutral Al2Cl6 dimers and charged AlCl4- monomers, respectively. In intermediate AlCl3-KCl compositions, the chemical speciation proves to be a very complex process, requiring over 0.5 nanosecond to reach an equilibrium distribution of multiple species. It is a consequence of the competitive formation and dissociation of additional species, including charged Al dimers, trimers, and tetramers. Here, the species formation occurs through ion exchange events, which we explain by computing free energy landscapes and employing a Marcus-like rate theory. We show that both interspecies and intraspecies ion exchanges are probable and are dictated by the local structural reorganization reflected in the change of local coulombic fields. The species distributions are validated by comparing computed Raman spectra and neutron structure factors with the available experimental data. We find an excellent simulation-experiment agreement in both cases. Nevertheless, Raman spectroscopy turns out to be particularly advantageous for distinguishing between unique species distributions because of the distinct vibrational signatures of different species. The mechanistic insight into reaction dynamics gained in this study will be essential for the advancement of molten salts as reactive media in high-temperature energy applications.
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Affiliation(s)
- Luke D Gibson
- Computational Sciences and Engineering Division, Oak Ridge National Laboratory P.O. Box 2008 Oak Ridge TN 37831 USA
| | - Santanu Roy
- Chemical Science Division, Oak Ridge National Laboratory P.O. Box 2008 Oak Ridge TN 37831 USA
| | - Rabi Khanal
- Computational Sciences and Engineering Division, Oak Ridge National Laboratory P.O. Box 2008 Oak Ridge TN 37831 USA
| | - Rajni Chahal
- Chemical Science Division, Oak Ridge National Laboratory P.O. Box 2008 Oak Ridge TN 37831 USA
| | - Ada Sedova
- Bioscience Division, Oak Ridge National Laboratory P.O. Box 2008 Oak Ridge TN 37831 USA
| | - Vyacheslav S Bryantsev
- Chemical Science Division, Oak Ridge National Laboratory P.O. Box 2008 Oak Ridge TN 37831 USA
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Chakraborty B, Wang J, Eapen J. Multicomponent diffusion in molten LiCl-KCl: dynamical correlations and divergent Maxwell-Stefan diffusivities. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 87:052312. [PMID: 23767545 DOI: 10.1103/physreve.87.052312] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2013] [Indexed: 06/02/2023]
Abstract
Multicomponent diffusional mechanisms in the ternary LiCl-KCl system are elucidated using the Green-Kubo formalism and equilibrium molecular dynamics simulations. The Maxwell-Stefan (MS) diffusion matrix is evaluated from the Onsager dynamical matrix that contains the diffusion flux correlation functions. From the temporal behavior of the correlation functions, we observe that the Li-Li and Li-Cl ion pairs have a pronounced cage dynamics that remains noticeably strong even at high temperatures. Even though the Onsager coefficients, which are the time integrals of the diffusion flux correlation functions, portray a relatively smooth variation across various compositions and temperatures, we observe a sign change and a divergent-like behavior for the MS diffusivity of the K-Li ion pair at a temperature of ~1100 K for the eutectic composition, and at a KCl mole fraction of ~0.49 at 1043 K. Negative MS diffusivities, while unusual, are however shown to satisfy the nonnegative entropic constraints.
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Affiliation(s)
- Brahmananda Chakraborty
- Department of Nuclear Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA
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Salanne M, Siqueira LJA, Seitsonen AP, Madden PA, Kirchner B. From molten salts to room temperature ionic liquids: Simulation studies on chloroaluminate systems. Faraday Discuss 2012; 154:171-88; discussion 189-220, 465-71. [DOI: 10.1039/c1fd00053e] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
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Freyland W. Liquid Metals, Molten Salts, and Ionic Liquids: Some Basic Properties. SPRINGER SERIES IN SOLID-STATE SCIENCES 2011. [DOI: 10.1007/978-3-642-17779-8_2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/12/2023]
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Li S, Cao Z, Peng Y, Liu L, Wang Y, Wang S, Wang JQ, Yan T, Gao XP, Song DY, Shen PW. Molecular dynamics simulation of LiTFSI-acetamide electrolytes: structural properties. J Phys Chem B 2008; 112:6398-410. [PMID: 18444674 DOI: 10.1021/jp710898h] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The liquid structures of nonaqueous electrolytes composed of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and acetamide, with LiTFSI/acetamide molar ratios of 1:2, 1:4, and 1:6, were studied by molecular dynamics simulations. The simulations indicate that the Li+ cations prefer to be six-coordinate by the sulfonyl oxygen atoms of the TFSI- anions and the carbonyl oxygen atoms of the acetamide molecules, rather than by the most electronegative nitrogen atom of the TFSI- anion. Therefore, close Li+-TFSI- contact pairs exist in the system. The TFSI- anion prefers to provide only one of four possible oxygen atoms to coordinate to the same Li+ cation. Three conformations (cis, trans, and gauche) of the TFSI- anions were found to coexist in the liquid electrolyte. At high salt concentrations, the TFSI- anions mainly adopt the gauche conformation in order to provide more oxygen atoms to coordinate to different Li+ cations, while simultaneously reducing the repulsion among the Li+ cations. On the other hand, the fraction of TFSI- anions adopting the cis conformation is largest for the system with the molar ratio of 1:6, in which many clusters, mainly composed of the Li+ cations and the TFSI- anions, are immersed in the acetamide molecules. The size and charge distribution of clusters were also investigated. In the system with the molar ratio of 1:2, nearly all of the ions in the PBC (periodic boundary conditions) box aggregate into a bulky cluster that gradually disassembles into small clusters with decreasing salt concentration. The addition of acetamide molecules was found to effectively relax the liquid electrolyte structure, and the system with the molar ratio of 1:4 was found to exhibit a more homogeneous liquid structure than the other two electrolyte systems with molar ratios of 1:2 and 1:6.
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Affiliation(s)
- Shu Li
- Institute of New Energy Material Chemistry, Department of Material Chemistry, Nankai University, Tianjin 300071, China
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The Chemical Environment of Ionic Liquids: Links Between Liquid Structure, Dynamics, and Solvation. ADVANCES IN CHEMICAL PHYSICS 2008. [DOI: 10.1002/9780470259498.ch2] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/13/2023]
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Ruberto R, Pastore G, Akdeniz Z, Tosi MP. Structure and diffusion in aluminium and gallium trihalide melts from simulations based on intramolecular force laws. Mol Phys 2007. [DOI: 10.1080/00268970701651706] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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9
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Brazhkin VV, Lyapin AG, Popova SV, Katayama Y, Saitoh H, Utsumi W. Molecular-network-ionic structure transitions in liquid AlCl(3) and ZnCl(2) halogenides under pressure. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2007; 19:246104. [PMID: 21694040 DOI: 10.1088/0953-8984/19/24/246104] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We present the in situ high-pressure-high-temperature x-ray diffraction study of the liquid AlCl(3) and ZnCl(2) halogenides having a quasi-molecular network structure in liquid state at normal pressure. These liquids are intermediate between pure covalent and ionic melts. Structural study of these liquid halogenides is indicative of a rapid and strong breakdown of an intermediate-range order in a tetrahedral network of melts for the initial pressure range, 0-2.5 GPa for AlCl(3) and 0-1.8 GPa for ZnCl(2), and points to rather sharp transitions in liquids with the formation of a short-range order structure similar to ionic melt structures around 4 GPa for AlCl(3) and 3 GPa for ZnCl(2). Thus, pseudo-covalent liquid halogenides like AlCl(3) and ZnCl(2) provide testimony to two phenomena under high pressures, namely, a gradual decay of structural correlations in the tetrahedral network of the melt and a sharp transition from molecular-network to ionic structure in liquid on further compression. Such a two-stage structural transformation under pressure is the general feature for a wide class of simple melts, including most of the pseudo-covalent halogenides.
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Affiliation(s)
- V V Brazhkin
- Institute for High Pressure Physics, Russian Academy of Sciences, Troitsk, Moscow region, 142190, Russia
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East ALL, Hafner J. Short-Range Order in Liquid Aluminum Chloride: Ab Initio Molecular Dynamics Simulations and Quantum-Chemical Calculations. J Phys Chem B 2007; 111:5316-21. [PMID: 17447811 DOI: 10.1021/jp070517y] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We use ab initio molecular dynamics simulations based on density-functional theory and quantum-chemistry calculations on molecular clusters to examine the structure of liquid AlCl3. In the past, conflicting descriptions of the short-range-order in molten AlCl3, based on either edge-sharing dimers or corner-sharing oligomers, have been proposed. This liquid also poses a simulation challenge, due to the possibility of ring-like trimers which can be metastable on the order of >10 ps. Simulations which begin with monomers, either random or ordered, appear to be able to produce proper ratios of ring-trimer to dimer-plus-tail molecular structures without the need to achieve long-time scale chemical equilibrium. Single-molecule calculations lend further support to the conclusion that the liquid is composed largely of edge-sharing dimers.
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Affiliation(s)
- A L L East
- Department of Chemistry and Biochemistry, University of Regina, Regina, Saskatchewan S4S 0A2, Canada
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Kirchner B, Seitsonen AP, Hutter J. Ionic Liquids from Car−Parrinello Simulations, Part I: Liquid AlCl3. J Phys Chem B 2006; 110:11475-80. [PMID: 16771422 DOI: 10.1021/jp061365u] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The properties of isolated AlCl3 clusters and the bulk system are investigated by means of static and dynamic electronic structure methods. We find important structural motifs with the edge connectivity dominant in a dimer and the corner connectivity dominant in a trimer. Furthermore, the trimer cluster exhibits an interesting ring structure with large cooperative effects relative to the dimer. Comparing the found structural motifs in isolated molecule calculations with the structure of the liquid allows us to determine the dominance of edge connectivity in the liquid. The size of the clusters present in the liquid indicates indeed that the dimer is the most abundant species, but there are also trimers, tetramers, and pentamers present. From the local dipole analysis both for the isolated clusters as well as for the liquid, further proof for the edge connectivity is given. However, all results point to the fact that there is also some small percentage of corner connectivity present that might be attributed to the most stable corner-connected cluster, namely the trimer. Importantly, we find that energetic considerations of isolated (static) clusters only do not represent the findings in liquid phase. Instead, a quantum cluster equilibrium approach or simulations are needed.
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Affiliation(s)
- Barbara Kirchner
- Lehrstuhl für Theoretische Chemie, Institut für Physikalische und Theoretische Chemie, Universität Bonn, Wegelerstr. 12, D-53115 Bonn, Germany.
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Madden PA, Wilson M, Hutchinson F. Raman spectra of ionic liquids: Interpretation via computer simulation. J Chem Phys 2004; 120:6609-20. [PMID: 15267553 DOI: 10.1063/1.1650831] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Theoretical Raman spectra of the complex-forming ionic liquids LaCl3 and ScCl3, derived from molecular dynamics computer simulations, are presented. These simulations, which use polarizable ion interaction models, have previously been shown to predict structural properties in excellent agreement with diffraction experiments. The dependence of the polarizability of the melt on the ionic positions, which determines the Raman spectrum through the time dependence of the polarizability correlation function, is modeled on the basis of ab initio electronic structure calculations carried out on alkali chlorides. New simulation techniques are introduced in order to allow the spectrum to be calculated with acceptable statistics. The calculated spectra are in semiquantitative agreement with experimental data. The distinctive bands which appear in the spectra of such complex melts are linked to the vibrations of the transient coordination complexes which form in these melts and new interpretations for the origin of several well-known features are proposed. The simulations thus enable a link between the structure of a melt as perceived through Raman spectroscopy and through diffraction experiments to be made.
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Affiliation(s)
- Paul A Madden
- Physical and Theoretical Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QZ, United Kingdom.
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Zissi GD, Papatheodorou GN. Composition and temperature induced changes on the structure of molten ScCl3–CsCl mixtures. Phys Chem Chem Phys 2004. [DOI: 10.1039/b408289c] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Lee YC, Kolafa J, Curtiss LA, Ratner MA, Shriver DF. Molten salt electrolytes. I. Experimental and theoretical studies of LiI/AlCl3. J Chem Phys 2001. [DOI: 10.1063/1.1372328] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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HUTCHINSON FRANCIS, WILSON MARK, MADDEN PAULA. A unified description of MCI3systems with a polarizable ion simulation model. Mol Phys 2001. [DOI: 10.1080/00268970010022878] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
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Van Hooydonk G. Gauge symmetry, chirality and parity effects in four-particle systems: Coulomb's law as a universal function for diatomic molecules. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2000; 56A:2273-2331. [PMID: 11075672 DOI: 10.1016/s1386-1425(00)00298-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Following recent work in search for a universal function (Van Hooydonk, Eur. J. Inorg. Chem., (1999), 1617), we test four symmetric +/- a(n)Rn potentials for reproducing molecular potential energy curves (PECs). Classical gauge symmetry for 1/R-potentials results in generic left right asymmetric PECs. A pair of symmetric perturbed Coulomb potentials is quantitatively in accordance with observed PECs. For a bond, a four-particle system, charge inversion (a parity effect, atom chirality) is the key to explain this shape generically. A parity adapted Hamiltonian reduces from ten to two terms and to a soluble Bohr-like formula, a Kratzer (1 - Re/R)2 potential. The result is similar to the combined action of spin and wave function symmetry upon the Hamiltonian in Heitler-London theory. Analytical perturbed Coulomb functions varying with (1 - Re/R) scale attractive and repulsive branches of PECs for 13 bonds H2, HF, LiH, KH, AuH, Li2, LiF, KLi, NaCs, Rb2, RbCs, Cs2 and I2 in a single straight line. The 400 turning points for 13 bonds are reproduced with a deviation of 0.007 A at both branches. For 230 points at the repulsive side, the deviation is 0.003 A. The perturbed electrostatic Coulomb law is a universal molecular function. Ab initio zero molecular parameter functions give PECs of acceptable quality, just using atomic ionisation energies. The function can be used as a model potential for inverting levels and gives a first principle's comparison of short- and long-range interactions, important for the study of cold atoms. Wave-packet dynamics, femto-chemistry applied to the crossing of covalent and ionic curves, can provide evidence for this theory. We anticipate this scale/shape invariant scheme applies to smaller scales in nuclear and high-energy particle physics. For larger gravitational scales (Newton 1/R potentials), problems with super-unification are discussed. Reactions between hydrogen and antihydrogen, feasible in the near future, will probably produce normal H2.
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Affiliation(s)
- G Van Hooydonk
- Department of Library Sciences, Ghent University, Belgium.
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Hutchinson F, Rowley AJ, Walters MK, Wilson M, Madden PA, Wasse JC, Salmon PS. Structure of molten MCl3 systems from a polarizable ion simulation model. J Chem Phys 1999. [DOI: 10.1063/1.479471] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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