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Kawai Y, Yamamoto Y, Kiyohara K. Selective adsorption of divalent and trivalent cations in porous electrodes. J Chem Phys 2024; 161:094701. [PMID: 39225524 DOI: 10.1063/5.0222272] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2024] [Accepted: 08/19/2024] [Indexed: 09/04/2024] Open
Abstract
The capacitive deionization technology uses the electrochemical adsorption of ions in porous electrodes to desalinate seawater or brackish water. Recently, capacitive deionization has gained significant attention as a technology for selective adsorption of ionic species from multicomponent aqueous electrolytes. To investigate the mechanism of selective adsorption at the molecular level, we performed molecular dynamics simulations of aqueous electrolytes and porous electrodes with different divalent or trivalent ions, electrode pore sizes, and applied voltages. We calculated the free energy barriers preventing ions from entering the pores of the electrode and the structure of the water molecules near the ions and the electrode surface under various conditions. Our results suggest that, when the pore and ion sizes are comparable, the steric and electrostatic interactions between the hydrated ions and electrode pores are comparable in magnitude. Moreover, the relative importance of the two interactions can be reversed by slight changes in the external conditions, such as the ion size, valence of the ions, electrode pore size, and applied voltage. Thus, by finely tuning the electrode pore size and the applied voltage, it may be possible to selectively adsorb a particular ionic species from a multicomponent electrolyte through capacitive deionization using a porous electrode.
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Affiliation(s)
- Yusuke Kawai
- Department of Chemistry, Graduate School of Science and Technology, Kwansei Gakuin University, Sanda, Hyogo 669-1337, Japan
| | - Yuji Yamamoto
- Department of Chemistry, Graduate School of Science and Technology, Kwansei Gakuin University, Sanda, Hyogo 669-1337, Japan
| | - Kenji Kiyohara
- Department of Chemistry, Graduate School of Science and Technology, Kwansei Gakuin University, Sanda, Hyogo 669-1337, Japan
- Research Institute of Electrochemical Energy, National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka 563-8577, Japan
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Nickel O, Ahrens-Iwers LJV, Meißner RH, Janssen M. Water, Not Salt, Causes Most of the Seebeck Effect of Nonisothermal Aqueous Electrolytes. PHYSICAL REVIEW LETTERS 2024; 132:186201. [PMID: 38759182 DOI: 10.1103/physrevlett.132.186201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2023] [Revised: 12/05/2023] [Accepted: 04/01/2024] [Indexed: 05/19/2024]
Abstract
A temperature difference between two electrolyte-immersed electrodes often yields a voltage Δψ between them. This electrolyte Seebeck effect is usually explained by cations and anions flowing differently in thermal gradients. However, using molecular simulations, we found almost the same Δψ for cells filled with pure water as with aqueous alkali halides. Water layering and orientation near polarizable electrodes cause a large temperature-dependent potential drop χ there. The difference in χ of hot and cold electrodes captures most of the thermovoltage, Δψ≈χ_{hot}-χ_{cold}.
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Affiliation(s)
- Ole Nickel
- Institute of Polymers and Composites, Hamburg University of Technology, Hamburg, Germany
| | | | - Robert H Meißner
- Institute of Polymers and Composites, Hamburg University of Technology, Hamburg, Germany
- Institute of Surface Science, Helmholtz-Zentrum Hereon, Geesthacht, Germany
| | - Mathijs Janssen
- Norwegian University of Life Sciences, Faculty of Science and Technology, Ås, Norway
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3
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Sitlapersad RS, Thornton AR, den Otter WK. Charging and discharging a supercapacitor in molecular simulations. J Chem Phys 2024; 160:044111. [PMID: 38275193 DOI: 10.1063/5.0177103] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2023] [Accepted: 12/17/2023] [Indexed: 01/27/2024] Open
Abstract
As the world moves more toward unpredictable renewable energy sources, better energy storage devices are required. Supercapacitors are a promising technology to meet the demand for short-term, high-power energy storage. Clearly, understanding their charging and discharging behaviors is essential to improving the technology. Molecular Dynamics (MD) simulations provide microscopic insights into the complex interplay between the dynamics of the ions in the electrolyte and the evolution of the charge distributions on the electrodes. Traditional MD simulations of (dis)charging supercapacitors impose a pre-determined evolving voltage difference between the electrodes, using the Constant Potential Method (CPM). Here, we present an alternative method that explicitly simulates the charge flow to and from the electrodes. For a disconnected capacitor, i.e., an open circuit, the charges are allowed to redistribute within each electrode while the sum charges on both electrodes remain constant. We demonstrate, for a model capacitor containing an aqueous salt solution, that this method recovers the charge-potential curve of CPM simulations. The equilibrium voltage fluctuations are related to the differential capacitance. We next simulate a closed circuit by introducing equations of motion for the sum charges, by explicitly accounting for the external circuit element(s). Charging and discharging of the model supercapacitor via a resistance proceed by double exponential processes, supplementing the usual time scale set by the electrolyte dynamics with a novel time scale set by the external circuit. Finally, we propose a simple equivalent circuit that reproduces the main characteristics of this supercapacitor.
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Affiliation(s)
- Ranisha S Sitlapersad
- Department of Fluid and Thermal Engineering and MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands
| | - Anthony R Thornton
- Department of Fluid and Thermal Engineering and MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands
| | - Wouter K den Otter
- Department of Fluid and Thermal Engineering and MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands
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Sitlapersad RS, Thornton AR, den Otter WK. A simple efficient algorithm for molecular simulations of constant potential electrodes. J Chem Phys 2024; 160:034107. [PMID: 38235800 DOI: 10.1063/5.0171502] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Accepted: 12/21/2023] [Indexed: 01/19/2024] Open
Abstract
Increasingly, society requires high power, high energy storage devices for applications ranging from electric vehicles to buffers on the electric grid. Supercapacitors are a promising contribution to meeting these demands, though there still remain unsolved practical problems. Molecular dynamics simulations can shed light on the relevant molecular level processes in electric double layer capacitors, but these simulations are computationally very demanding. Our focus here is on the algorithmic complexity of the constant potential method (CPM), which uses dedicated electrostatics solvers to maintain a fixed potential difference between two conducting electrodes. We show how any standard electrostatics solver-capable of calculating the energies and forces on all atoms-can be used to implement CPM with a minimum of coding. As an example, we compare our generalized implementation of CPM, based on invocations of the particle-particle-particle-mesh routine of the Large-scale Atomic/Molecular Massively Parallel Simulator, with a traditional implementation based on a dedicated re-implementation of Ewald summation. Both methods yield comparable results on four test systems, with the former achieving a substantial gain in speed and improved scalability. The step from dedicated electrostatic solvers to generic routines is made possible by noting that CPM's traditional narrow Gaussian point-spread of atomic charges on the electrodes effectively endows point-like atoms with chemical hardness, i.e., an intra-atomic energy quadratic in the charge.
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Affiliation(s)
- Ranisha S Sitlapersad
- Department of Fluid and Thermal Engineering and MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands
| | - Anthony R Thornton
- Department of Fluid and Thermal Engineering and MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands
| | - Wouter K den Otter
- Department of Fluid and Thermal Engineering and MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands
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Dawlaty JM, Perkin S, Salanne M, Willard AP. The chemical physics of electrode-electrolyte interfaces. J Chem Phys 2023; 159:150401. [PMID: 37846953 DOI: 10.1063/5.0177099] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2023] [Accepted: 09/25/2023] [Indexed: 10/18/2023] Open
Affiliation(s)
- Jahan M Dawlaty
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA
| | - Susan Perkin
- Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford OX1 3QZ, United Kingdom
| | - Mathieu Salanne
- Sorbonne Université, CNRS, Physicochimie des Électrolytes et Nanosystèmes Interfaciaux, F-75005 Paris, France
| | - Adam P Willard
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 01239, USA
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Jiménez-Ángeles F, Ehlen A, Olvera de la Cruz M. Surface polarization enhances ionic transport and correlations in electrolyte solutions nanoconfined by conductors. Faraday Discuss 2023; 246:576-591. [PMID: 37450272 DOI: 10.1039/d3fd00028a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/13/2023]
Abstract
Layered materials that perform mixed electron and ion transport are promising for energy harvesting, water desalination, and bioinspired functionalities. These functionalities depend on the interaction between ionic and electronic charges on the surface of materials. Here we investigate ion transport by an external electric field in an electrolyte solution confined in slit-like channels formed by two surfaces separated by distances that fit only a few water layers. We study different electrolyte solutions containing monovalent, divalent, and trivalent cations, and we consider walls made of non-polarizable surfaces and conductors. We show that considering the surface polarization of the confining surfaces can result in a significant increase in ionic conduction. The ionic conductivity is increased because the conductors' screening of electrostatic interactions enhances ionic correlations, leading to faster collective transport within the slit. While important, the change in water's dielectric constant in confinement is not enough to explain the enhancement of ion transport in polarizable slit-like channels.
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Affiliation(s)
- Felipe Jiménez-Ángeles
- Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA.
| | - Ali Ehlen
- Applied Physics Program, Northwestern University, Evanston, Illinois 60208, USA
| | - Monica Olvera de la Cruz
- Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA.
- Applied Physics Program, Northwestern University, Evanston, Illinois 60208, USA
- Department of Physics, Northwestern University, Evanston, Illinois 60208, USA
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Ahrens-Iwers LJ, Janssen M, Tee SR, Meißner RH. ELECTRODE: An electrochemistry package for atomistic simulations. J Chem Phys 2022; 157:084801. [DOI: 10.1063/5.0099239] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Constant potential methods (CPM) enable computationally efficient simulations of the solid-liquid interface at conducting electrodes in molecular dynamics (MD). They have been successfully used, for example, to realistically model the behavior of ionic liquids or water-in-salt electrolytes in supercapacitors and batteries. The CPM models conductive electrodes by updating charges of individual electrode atoms according to the applied electric potential and the (time-dependent) local electrolyte structure. Here we present a feature-rich CPM implementation, called ELECTRODE, for the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS), which includes a constrained charge method and a thermo-potentiostat. The ELECTRODE package also contains a finite-field approach, multiple corrections for non-periodic boundary conditions of the particle-particle particle-mesh solver, and a Thomas-Fermi model for using non-ideal metals as electrodes. We demonstrate the capabilities of this implementation for a parallel-plate electrical double-layer capacitor, for which we have investigated the charging times with the different implemented methods and found an interesting relationship between water and ionic dipole relaxations. To prove the validity of the one-dimensional correction for the long-range electrostatics, we estimated the vacuum capacitance of two co-axial carbon nanotubes and compared it to structureless cylinders, for which an analytical expression exists. In summary, the ELECTRODE package enables efficient electrochemical simulations using state-of-the-art methods, allowing one to simulate even heterogeneous electrodes. Moreover, it allows unveiling more rigorously how electrode curvature affects the capacitance with the one-dimensional correction.
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Affiliation(s)
| | | | - Shern Ren Tee
- The University of Queensland Australian Institute for Bioengineering and Nanotechnology, Australia
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Jeanmairet G, Rotenberg B, Salanne M. Microscopic Simulations of Electrochemical Double-Layer Capacitors. Chem Rev 2022; 122:10860-10898. [PMID: 35389636 PMCID: PMC9227719 DOI: 10.1021/acs.chemrev.1c00925] [Citation(s) in RCA: 45] [Impact Index Per Article: 22.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2021] [Indexed: 12/19/2022]
Abstract
Electrochemical double-layer capacitors (EDLCs) are devices allowing the storage or production of electricity. They function through the adsorption of ions from an electrolyte on high-surface-area electrodes and are characterized by short charging/discharging times and long cycle-life compared to batteries. Microscopic simulations are now widely used to characterize the structural, dynamical, and adsorption properties of these devices, complementing electrochemical experiments and in situ spectroscopic analyses. In this review, we discuss the main families of simulation methods that have been developed and their application to the main family of EDLCs, which include nanoporous carbon electrodes. We focus on the adsorption of organic ions for electricity storage applications as well as aqueous systems in the context of blue energy harvesting and desalination. We finally provide perspectives for further improvement of the predictive power of simulations, in particular for future devices with complex electrode compositions.
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Affiliation(s)
- Guillaume Jeanmairet
- Sorbonne
Université, CNRS, Physico-chimie
des Électrolytes et Nanosystèmes Interfaciaux, PHENIX, F-75005 Paris, France
- Réseau
sur le Stockage Electrochimique de l’Energie (RS2E), FR CNRS
3459, 80039 Amiens, France
| | - Benjamin Rotenberg
- Sorbonne
Université, CNRS, Physico-chimie
des Electrolytes et Nanosystèmes Interfaciaux, PHENIX, F-75005 Paris, France
- Réseau
sur le Stockage Électrochimique de l’Énergie
(RS2E), FR CNRS 3459, 80039 Amiens, France
| | - Mathieu Salanne
- Réseau
sur le Stockage Electrochimique de l’Energie (RS2E), FR CNRS
3459, 80039 Amiens, France
- Sorbonne
Université, CNRS, Physico-chimie
des Electrolytes et Nanosystèmes Interfaciaux, PHENIX, F-75005 Paris, France
- Institut
Universitaire de France (IUF), 75231 Paris Cedex 05, France
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Tee SR, Searles DJ. Fully periodic, computationally efficient constant potential molecular dynamics simulations of ionic liquid supercapacitors. J Chem Phys 2022; 156:184101. [DOI: 10.1063/5.0086986] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Molecular dynamics (MD) simulations of complex electrochemical systems, such as ionic liquid supercapacitors, are increasingly including the constant potential method (CPM) to model conductive electrodes at a specified potential difference, but the inclusion of CPM can be computationally expensive. We demonstrate the computational savings available in CPM MD simulations of ionic liquid supercapacitors when the usual non-periodic slab geometry is replaced with fully periodic boundary conditions. We show how a doubled cell approach, previously used in non-CPM MD simulations of charged interfaces, can be used to enable fully periodic CPM MD simulations. Using either a doubled cell approach or a finite field approach previously reported by others, fully periodic CPM MD simulations produce comparable results to the traditional slab geometry simulations with a nearly double speedup in computational time. Indeed, these savings can offset the additional cost of the CPM algorithm, resulting in periodic CPM MD simulations that are computationally competitive with the non-periodic, fixed charge equivalent simulations for the ionic liquid supercapacitors studied here.
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Affiliation(s)
- Shern R. Tee
- Australian Institute of Bioengineering and Nanotechnology, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Debra J. Searles
- Australian Institute of Bioengineering and Nanotechnology, The University of Queensland, Brisbane, QLD 4072, Australia
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia
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Gäding J, Tocci G, Busch M, Huber P, Meißner RH. Impact of confinement and polarizability on dynamics of ionic liquids. J Chem Phys 2022; 156:064703. [DOI: 10.1063/5.0077408] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Johannes Gäding
- Institute of Polymers and Composites, Hamburg University of Technology, 21073 Hamburg, Germany
| | - Gabriele Tocci
- Department of Chemistry, University of Zurich, 8057 Zürich, Switzerland
| | - Mark Busch
- Institute for Materials and X-Ray Physics, Hamburg University of Technology, 21073 Hamburg, Germany
- Deutsches Elektronen-Synchrotron DESY, Centre for X-Ray and Nano Science CXNS, 22607 Hamburg, Germany
- Centre for Hybrid Nanostructures CHyN, Hamburg University, 22761 Hamburg, Germany
| | - Patrick Huber
- Institute for Materials and X-Ray Physics, Hamburg University of Technology, 21073 Hamburg, Germany
- Deutsches Elektronen-Synchrotron DESY, Centre for X-Ray and Nano Science CXNS, 22607 Hamburg, Germany
- Centre for Hybrid Nanostructures CHyN, Hamburg University, 22761 Hamburg, Germany
| | - Robert H. Meißner
- Institute of Polymers and Composites, Hamburg University of Technology, 21073 Hamburg, Germany
- Helmholtz-Zentrum Hereon, Institute of Surface Science, 21502 Geesthacht, Germany
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