scholarly journals Effects of Hydration and Temperature on the Microstructure and Transport Properties of Nafion Polyelectrolyte Membrane: A Molecular Dynamics Simulation

Membranes ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 695
Author(s):  
Guoling Zhang ◽  
Guogang Yang ◽  
Shian Li ◽  
Qiuwan Shen ◽  
Hao Wang ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Diffusion Coefficient ◽  
Water Content ◽  
Water Clusters ◽  
Polymer Electrolyte Membrane ◽  
Distribution Functions ◽  
Dynamics Simulation ◽  
Water Molecules ◽  
Hydration Level ◽  
Hydronium Ions

To investigate the effects of temperature and hydration on the microstructure of polymer electrolyte membrane and the transport of water molecules and hydronium ions, molecular dynamics simulations are performed on Nafion 117 for a series of water contents at different temperatures. The interactions among the sulfonate groups, hydronium ions, and water molecules are studied according to the analysis of radial distribution functions and coordination numbers. The sizes and connectivity of water clusters are also discussed, and it is found that the hydration level plays a key role in the phase separation of the membrane. However, the effect of the temperature is slight. When the water content increases from 3.5 to 16, the size of water clusters in the membrane increases, and the clusters connect to each other to form continuous channels for diffusion of water molecules and hydronium ions. The diffusion coefficients are estimated by studying the mean square displacements. The results show that the diffusion of water molecules and hydronium ions are both enhanced by the increase of the temperature and hydration level. Furthermore, the diffusion coefficient of water molecules is always much larger than that of hydronium ions. However, the ratio of the diffusion coefficient of water molecules to that of hydronium ions decreases with the increase of water content.

Molecular Dynamics Study of Proton and Water Transport in Nafion Membrane

2013 ◽  
Author(s):  
Takuya Mabuchi ◽  
Takashi Tokumasu
Keyword(s):  
Experimental Data ◽  
Molecular Dynamics ◽  
Diffusion Coefficient ◽  
Water Clusters ◽  
Nafion Membrane ◽  
Water Molecules ◽  
Static Structure ◽  
Hydration Level ◽  
Hydronium Ions ◽  
Structure Factors

Polymer electrolyte fuel cells (PEFCs) are highly expected as a next-generation power supply system due to the purity of its exhaust gas, its high power density and high efficiency. The polymer electrolyte membrane is a critical component for the performance of the PEFCs and it is important to understand the nanostructure in the membrane to enhance proton transport. We have performed an atomistic analysis of the vehicular transport of hydronium ions and water molecules in the nanostructure of hydrated Nafion membrane by systematically changing the hydration level which provides insights into a connection between the nanoscopic and mesoscopic structure of ion clusters and the dynamics of hydronium ions and water molecules in the hydrated Nafion membrane. In this study, classical molecular dynamics simulations are implemented using a model of Nafion membrane which is based on DREIDING force field and newly modified and validated by comparing the density, water diffusivity, and Nafion morphology with experimental data. The simulated final density after the annealing procedure agrees with experiment within 1.3 % for various water contents and the trends that density decreases with increasing hydration level are reproduced. In addition to determination of diffusion coefficients of solvent molecules as a function of hydration level (from λ = 1 up to λ = 18), we have also calculated radial distribution functions and static structure factors not only to clarify the structure of water molecules and hydronium ions around the first solvation shell of sulfonate groups but also to validate the mesoscopic periodic structure among water clusters. The diffusion coefficient of water molecules increases with increasing hydration level and is found to be in good agreement with experimental data. The diffusion coefficient of hydronium ions has showed that general trends in the experimental data are reproduced by the simulations although the classical models have the limitation of probing hydronium dynamics. The static structure factors of liquid molecules at low wave length provide insights into the periodic structure of the inter-water clusters. These results are consistent with the Gebel’s model based on small-angle X-ray scattering that considers the dry membrane to be made of isolated spherical ionic clusters of radius ∼7.5 Å that swell with increasing hydration.

A Molecular Dynamics Study of the Structure of an Aqueous CsF Solution

1983 ◽  
Vol 38 (2) ◽  
pp. 214-224 ◽  
Author(s):  
Gy. I. Szász ◽  
K. Heinzinger
Keyword(s):  
Molecular Dynamics ◽  
Hydration Shell ◽  
Distribution Functions ◽  
Dynamics Simulation ◽  
Water Model ◽  
Water Molecules ◽  
Heat Of Solution ◽  
Average Temperature ◽  
Experimental Density ◽  
First Hydration Shell

Abstract A molecular dynamics simulation of a 2.2 molal aqueous CsF solution has been performed employing the ST2 water model. The basic periodic cube with a sidelength of 18.50 Å contained 200 water molecules, and 8 ions of each kind, corresponding to an experimental density of 1.26 g/cm3. The simulation extended over 6.5 ps with an average temperature of 307 K. The structure of the solution is discussed by means of radial distribution functions and the orientation of the water molecules. The computed hydration numbers in the first shell of Cs+ and F- are 7.9 and 6.8, respectively; the corresponding first hydration shell radii are 3.22 A and 2.64 A, respectively. Values for the hydration shell energies and the heat of solution have been calculated.

Study on Diffusion Processes of Water and Proton in PEM Using Molecular Dynamics Simulation

2011 ◽  
Vol 704-705 ◽  
pp. 1266-1272 ◽  
Author(s):  
Lei Chen ◽  
Wen Quan Tao
Keyword(s):  
Experimental Data ◽  
Molecular Dynamics ◽  
Water Content ◽  
Diffusion Processes ◽  
Calculation Model ◽  
Dynamics Simulation ◽  
Water Molecules ◽  
Hydrogen Ions ◽  
Model Cell ◽  
Dynamics Calculation

In this paper a molecular dynamics calculation model for the Nafion 117 membrane is constructed by Materials Studio (MS) software platform to study its micro-structure and transport properties. Based on the calculation model, cell structures of different water content of Nafion 117 membrane are obtained and the predicted density values of simulated cell are in good agreement with experimental data. Meanwhile, the diffusion processes of water molecules and hydrogen ions in the membrane are studied, respectively. The predicted diffusion coefficients of both water molecules and hydrogen ions increase with the water content, which agrees well with the variation trend of experimental data. The reasons for the deviation between numerical results and the experiment values in literature are analyzed.

scholarly journals Effect of perfluorosulfonic acid side chains on oxygen permeation in hydrated ionomers of PEMFCs: Molecular dynamics simulation approach

2020 ◽  
Author(s):  
Sung Hyun Kwon ◽  
Haisu Kang ◽  
Young-Jun Sohn ◽  
Jinhee Lee ◽  
Sunbo Shim ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Water Content ◽  
Polymer Electrolyte Membrane ◽  
Md Simulations ◽  
Dynamics Simulation ◽  
Side Chain ◽  
Side Chains ◽  
Perfluorosulfonic Acid ◽  
Short Side ◽  
Water Contents

Abstract We prepared two types of perfluorosulfonic acid (PFSA) ionomers with Aquivion (short side chain) and Nafion (long side chain) on a Pt surface and varied their water contents (2.92 ≤ λ ≤ 13.83) to calculate the solubility and permeability of O2 in hydrated PFSA ionomers on a Pt surface using full atomistic molecular dynamics (MD) simulations. The solubility and permeability of O2 molecules in hydrated Nafion ionomers were greater than those of O2 molecules in hydrated Aquivion ionomers at the same water content, indicating that the permeation of O2 molecules in the ionomers is affected not only by the diffusion coefficient of O2 but also by the solubility of O2. Notably, O2 molecules are more densely distributed in regions where water and hydronium ions have a lower density in hydrated Pt/PFSA ionomers. Radial distribution function (RDF) analysis was performed to investigate where O2 molecules preferentially dissolve in PFSA ionomers on a Pt surface. The results showed that O2 molecules preferentially dissolved between hydrophilic and hydrophobic regions in a hydrated ionomer. The RDF analysis was performed to provide details of the O2 location in hydrated PFSA ionomers on a Pt surface to evaluate the influence of O2 solubility in ionomers with side chains of different lengths. The coordination number of C(center)–O(O2) and O(side chain)–O(O2) pairs in hydrated Nafion ionomers was higher than that of the same pairs in hydrated Aquivion ionomers with the same water content. Our investigation provides detailed information about the properties of O2 molecules in different PFSA ionomers on a Pt surface and with various water contents, potentially enabling the design of better-performing PFSA ionomers for use in polymer electrolyte membrane fuel cells.

scholarly journals Effects of Temperature on Structural Properties of Hydrated Montmorillonite: Experimental Study and Molecular Dynamics Simulation

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Wangbing Hong ◽  
Jie Meng ◽  
Changdong Li ◽  
Shengyi Yan ◽  
Xin He ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Water Content ◽  
Structural Properties ◽  
Environmental Changes ◽  
Electrostatic Force ◽  
Dynamics Simulation ◽  
Water Molecules ◽  
Interlayer Water ◽  
Layer Spacing ◽  
Bonding Structure

Montmorillonite (MMT) is highly sensitive to environmental changes and therefore plays a key role in the structural evolution of rocks and soils and even damage and disasters. The effects of important environmental factors (the temperature and water content) on MMT structural properties require in-depth study. The structure and morphology of sodium montmorillonite (Na-MMT) and its thermal products (micro-nanoparticles) were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). A molecular dynamics (MD) simulation was performed to investigate how temperature (below the failure temperature of the Na-MMT crystal layer) affects the structural properties of hydrated MMT. (1) The laboratory results showed that increasing the temperature significantly affected water molecules, and the particle aggregates exhibited inhomogeneous thermal expansion. The interlayer structure collapsed at 500–700°C. (2) In the simulation, the pull-off force inhibited interactions among oxides, crystal layers on both sides of the sample, and the bonding structure of water molecules, thus exposing the stress on the bonding body for analysis. The MMT ultimate stresses in the X, Y, and Z directions all trended downward with increasing water content and temperature. (3) Environmentally induced damage was most likely to occur in the Z direction. Increasing the number of interlayer water molecules increased the layer spacing and considerably weakened van der Waals forces, such that the roles of the electrostatic force and the interlayer hydrogen bond network gradually became significant. The most significant impact of increasing the temperature was reflected in the hydrogen bonding network, resulting in the destruction of the interlayer water bridge, the gradual failure of the layered bonding structure, and the formation or development of cracks. This improved understanding of the structural properties of MMT aggregates under environmental change advances research on the evolutionary behaviour of nano-, micro-, and macrostructures of rocks and soils.

Molecular Dynamics Study of Oxygen Permeation Through the Ionomer of PEFC Catalyst Layer

2011 ◽  
Author(s):  
Kiminori Sakai ◽  
Takashi Tokumasu
Keyword(s):  
Molecular Dynamics ◽  
Water Content ◽  
Polymer Electrolyte Membrane ◽  
Catalyst Layer ◽  
Oxygen Permeation ◽  
Dynamics Simulation ◽  
Cathode Side ◽  
Catalytic Surface ◽  
Electrolyte Membrane ◽  
Cathode Catalyst Layer

Polymer electrolyte membrane fuel cell (PEFC) is focused worldwide as the energy conversion device of next generation. In the PEFC cathode catalyst layer, an ionomer with which the catalyst is covered is very important on the point of transferring protons to the catalytic surface on the cathode side. On the other hand, it is said that an ionomer interferes with oxygen permeation to the catalytic surface. The mechanism of oxygen permeation through an ionomer was not analyzed in detail because it is too small to research by experiment. Moreover molecular dynamics simulation of the catalyst layer and oxygen permeability has not yet studied. In this research, we constructed the system including nafion, water, oxonium ion, platinum layers by using molecular dynamics study, and studied about the effect of the water content of the ionomer on the structure of the ionomer and permeability of the oxygen molecule. As the results, a lot of oxygen molecules permeated through a dried ionomer and reached to the catalytic surface but there were few oxygen molecules that permeated through a hydrated ionomer and reached there. In addition, it is found that the shape of the ionomer in the case of water content rate γ = 3, 7, 11 changed.

Molecular Dynamics Simulation of Quasi-Two-Dimensional Water Network on Ice Nucleation Protein

2011 ◽  
Author(s):  
Daisuke Murakami ◽  
Kenji Yasuoka
Keyword(s):  
Molecular Dynamics ◽  
Water Clusters ◽  
Ice Nucleation ◽  
Dynamics Simulation ◽  
Water Molecules ◽  
Two Dimensional ◽  
Threshold Density ◽  
Ice Nucleation Protein ◽  
Network Of Hydrogen Bonds ◽  
Dynamics Simulations

An ice nucleation protein induces a phase transition from liquid water to ice in air. A specific hydrophilic surface of the protein may have an influence on the network of hydrogen bonds touching on the protein. However, microscopic characteristics of the ice nucleation protein and behavior of water molecules on it have not been clarified. So we carried out molecular dynamics simulations in various quasi-two-dimensional densities of water molecules on the ice nucleation protein. The percolation threshold of water clusters was confirmed. Comparing another hydrophilic protein, the threshold density in both cases had nearly the same value. But percolation probabilities and mean cluster sizes near the threshold were different between both cases. Those results implied that the threshold density was consistent with the conventional theory, but the forming of water clusters near the threshold was influenced by the hydrophilicity on the ice nucleation protein.

Proton Transport in Nafion117 Membranes by Molecular Dynamics

2010 ◽  
Vol 105-106 ◽  
pp. 647-649
Author(s):  
Tie Jun Wu ◽  
Yu Hou Wu ◽  
Hong Sun ◽  
Yu Lan Tang
Keyword(s):  
Molecular Dynamics ◽  
Water Content ◽  
Proton Transport ◽  
Md Simulation ◽  
Acid Group ◽  
Distribution Functions ◽  
Water Molecules ◽  
Angle Bend ◽  
Low Temperature Fuel Cells ◽  
Oxygen Atoms

A molecular dynamics model was performed to study the proton transport of Nafion series membrane which is often used in low temperature fuel cells. The simulations intents to investigate the microstructure and the phenomenon of the proton transport processing. The model includes all-atom of main and side chains. The force field includes intermolecular Coulomb and Lennard-Jones terms and intra-molecular terms for harmonic bond stretch potentials, harmonic angle bend potentials and cosine terms for the torsions. The simulations were carried out in two cube systems at different temperature where water content differed from 5 and 10 water molecules per acid group in the polymer, respectively. The results showed that proton transport affected with water content by analyses of snap- shots of the MD simulation, the radial distribution functions between the sulfur atoms of SO3− groups, between the oxygen atoms of H3O+ ions, between oxygen atoms of water molecules and Nafion atoms at various stages.

Molecular Dynamics Simulation of an Aqueous MgCl2 Solution. Structural Results

1982 ◽  
Vol 37 (9) ◽  
pp. 1038-1048 ◽  
Author(s):  
W. Dietz ◽  
W. O. Riede ◽  
K. Heinzinger
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Hydration Shell ◽  
Distribution Functions ◽  
Dynamics Simulation ◽  
Water Molecules ◽  
Force Model ◽  
Average Temperature ◽  
Pair Potentials ◽  
Effective Pair

Abstract A molecular dynamics simulation of a 1.1 molal aqueous MgCl2 solution has been performed employing the central force model for water. The effective pair potentials for ion-water have been derived from ab initio calculations. The basic box with a sidelength of 18.30 Å contained 200 water molecules, 8 anions and 4 cations, corresponding to an experimental density of 1.079 g/cm3 . The simulation extended over about 3.3 picoseconds at an average temperature of 309 K. The structure of the solution is described by radial distribution functions and the orientation of the water molecules in respect to physically meaningful directions. Values for the dielectric constant and hydration energies have been calculated. The strong influences of the twofold charged magnesium ion on the geometry of the water molecules and the structure of the hydration shell is discussed in comparison with the results of a previous simulation of a 2.2 molal NaCl solution.

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