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Electro-osmotic Drag and Thermodynamic Properties of Water in Hydrated Nafion Membranes from Molecular Dynamics

[Image: see text] One of the important parameters in water management of proton exchange membranes is the electro-osmotic drag (EOD) coefficient of water. The value of the EOD coefficient is difficult to justify, and available literature data on this for Nafion membranes show scattering from in expe...

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Autores principales: Rahbari, Ahmadreza, Hartkamp, Remco, Moultos, Othonas A., Bos, Albert, van den Broeke, Leo J. P., Ramdin, Mahinder, Dubbeldam, David, Lyulin, Alexey V., Vlugt, Thijs J. H.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: American Chemical Society 2022
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9109139/
https://www.ncbi.nlm.nih.gov/pubmed/35592735
http://dx.doi.org/10.1021/acs.jpcc.2c01226
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author Rahbari, Ahmadreza
Hartkamp, Remco
Moultos, Othonas A.
Bos, Albert
van den Broeke, Leo J. P.
Ramdin, Mahinder
Dubbeldam, David
Lyulin, Alexey V.
Vlugt, Thijs J. H.
author_facet Rahbari, Ahmadreza
Hartkamp, Remco
Moultos, Othonas A.
Bos, Albert
van den Broeke, Leo J. P.
Ramdin, Mahinder
Dubbeldam, David
Lyulin, Alexey V.
Vlugt, Thijs J. H.
author_sort Rahbari, Ahmadreza
collection PubMed
description [Image: see text] One of the important parameters in water management of proton exchange membranes is the electro-osmotic drag (EOD) coefficient of water. The value of the EOD coefficient is difficult to justify, and available literature data on this for Nafion membranes show scattering from in experiments and simulations. Here, we use a classical all-atom model to compute the EOD coefficient and thermodynamic properties of water from molecular dynamics simulations for temperatures between 330 and 420 K, and for different water contents between λ = 5 and λ = 20. λ is the ratio between the moles of water molecules to the moles of sulfonic acid sites. This classical model does not capture the Grotthuss mechanism; however, it is shown that it can predict the EOD coefficient within the range of experimental values for λ = 5 where the vehicular mechanism dominates proton transfer. For λ > 5, the Grotthuss mechanism becomes dominant. To obtain the EOD coefficient, average velocities of water and ions are computed by imposing different electric fields to the system. Our results show that the velocities of water and hydronium scale linearly with the electric field, resulting in a constant ratio of ca. 0.4 within the error bars. We find that the EOD coefficient of water linearly increases from 2 at λ = 5 to 8 at λ = 20 and the results are not sensitive to temperature. The EOD coefficient at λ = 5 is within the range of experimental values, confirming that the model can capture the vehicular transport of protons well. At λ = 20, due to the absence of proton hopping in the model, the EOD coefficient is overestimated by a factor of 3 compared to experimental values. To analyze the interactions between water and Nafion, the partial molar enthalpies and partial molar volumes of water are computed from molecular dynamics simulations. At different water uptakes, multiple linear regression is used on raw simulation data within a narrow composition range of water inside the Nafion membrane. The partial molar volumes and partial molar excess enthalpies of water asymptotically approach the molar volumes and molar excess enthalpies of pure water for water uptakes above 5. This confirms the model can capture the bulklike behavior of water in the Nafion at high water uptakes.
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spelling pubmed-91091392022-05-17 Electro-osmotic Drag and Thermodynamic Properties of Water in Hydrated Nafion Membranes from Molecular Dynamics Rahbari, Ahmadreza Hartkamp, Remco Moultos, Othonas A. Bos, Albert van den Broeke, Leo J. P. Ramdin, Mahinder Dubbeldam, David Lyulin, Alexey V. Vlugt, Thijs J. H. J Phys Chem C Nanomater Interfaces [Image: see text] One of the important parameters in water management of proton exchange membranes is the electro-osmotic drag (EOD) coefficient of water. The value of the EOD coefficient is difficult to justify, and available literature data on this for Nafion membranes show scattering from in experiments and simulations. Here, we use a classical all-atom model to compute the EOD coefficient and thermodynamic properties of water from molecular dynamics simulations for temperatures between 330 and 420 K, and for different water contents between λ = 5 and λ = 20. λ is the ratio between the moles of water molecules to the moles of sulfonic acid sites. This classical model does not capture the Grotthuss mechanism; however, it is shown that it can predict the EOD coefficient within the range of experimental values for λ = 5 where the vehicular mechanism dominates proton transfer. For λ > 5, the Grotthuss mechanism becomes dominant. To obtain the EOD coefficient, average velocities of water and ions are computed by imposing different electric fields to the system. Our results show that the velocities of water and hydronium scale linearly with the electric field, resulting in a constant ratio of ca. 0.4 within the error bars. We find that the EOD coefficient of water linearly increases from 2 at λ = 5 to 8 at λ = 20 and the results are not sensitive to temperature. The EOD coefficient at λ = 5 is within the range of experimental values, confirming that the model can capture the vehicular transport of protons well. At λ = 20, due to the absence of proton hopping in the model, the EOD coefficient is overestimated by a factor of 3 compared to experimental values. To analyze the interactions between water and Nafion, the partial molar enthalpies and partial molar volumes of water are computed from molecular dynamics simulations. At different water uptakes, multiple linear regression is used on raw simulation data within a narrow composition range of water inside the Nafion membrane. The partial molar volumes and partial molar excess enthalpies of water asymptotically approach the molar volumes and molar excess enthalpies of pure water for water uptakes above 5. This confirms the model can capture the bulklike behavior of water in the Nafion at high water uptakes. American Chemical Society 2022-05-03 2022-05-12 /pmc/articles/PMC9109139/ /pubmed/35592735 http://dx.doi.org/10.1021/acs.jpcc.2c01226 Text en © 2022 The Authors. Published by American Chemical Society https://creativecommons.org/licenses/by/4.0/Permits the broadest form of re-use including for commercial purposes, provided that author attribution and integrity are maintained (https://creativecommons.org/licenses/by/4.0/).
spellingShingle Rahbari, Ahmadreza
Hartkamp, Remco
Moultos, Othonas A.
Bos, Albert
van den Broeke, Leo J. P.
Ramdin, Mahinder
Dubbeldam, David
Lyulin, Alexey V.
Vlugt, Thijs J. H.
Electro-osmotic Drag and Thermodynamic Properties of Water in Hydrated Nafion Membranes from Molecular Dynamics
title Electro-osmotic Drag and Thermodynamic Properties of Water in Hydrated Nafion Membranes from Molecular Dynamics
title_full Electro-osmotic Drag and Thermodynamic Properties of Water in Hydrated Nafion Membranes from Molecular Dynamics
title_fullStr Electro-osmotic Drag and Thermodynamic Properties of Water in Hydrated Nafion Membranes from Molecular Dynamics
title_full_unstemmed Electro-osmotic Drag and Thermodynamic Properties of Water in Hydrated Nafion Membranes from Molecular Dynamics
title_short Electro-osmotic Drag and Thermodynamic Properties of Water in Hydrated Nafion Membranes from Molecular Dynamics
title_sort electro-osmotic drag and thermodynamic properties of water in hydrated nafion membranes from molecular dynamics
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9109139/
https://www.ncbi.nlm.nih.gov/pubmed/35592735
http://dx.doi.org/10.1021/acs.jpcc.2c01226
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