Conductance Measurements in an Electrolytic Membrane Cell at Elevated Temperatures and Pressures

Steck, A.; Yeager, H. L.

doi:10.1149/1.2119941

Cited by 13 publications

(9 citation statements)

References 12 publications

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“…The transport of ions in synthetic nanomaterials, such as carbon nanotubes and mesoporous carbons, can also control technologies such as batteries and fuel cells. Experimental studies of ionic transport in well-defined micropores and membranes were attempted earlier. − There are, however, rare reports of precise and well-controlled experiments to quantify ionic transport in well-defined nanopores . Molecular dynamics simulations can often provide interim and complementary answers.…”

Section: Introductionmentioning

confidence: 99%

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Structural and Transport Properties of an SPC/E Electrolyte in a Nanopore

2004

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Equilibrium (EMD) and nonequilibrium molecular dynamics (NEMD) simulations were conducted to investigate the effects of confinement on the structural and transport properties of an electrolyte in a nanopore. The extended simple point charge (SPC/E) model was used to model water molecules in a 0.5 M KCl electrolyte. The cylindrical nanopore was smooth, structureless, and hydrophobic with a radius that varied from 4.75 to 15.8 Å. Changes in energies and structures were observed as the nanopore radius varied. The ion-ion, ionwater, and water-water interaction energies, the ion-ion and ion-water pair distribution functions, the density profiles of H and O atoms, and the water orientation about the vertical axis and around an ion were calculated in the simulations. Because of confinement in the radial direction in a narrow pore, there was incomplete solvation of ions, evidenced by less negative ion-water energy and less alignment of water molecules with the field of the ion. With a stronger confinement, H-bonding decreased, whereas the external field had a stronger influence on the orientation of the water molecules. Both EMD and NEMD results showed a decrease of ionic conductivity with decreasing pore radius, but there was an appreciable discrepancy between the conductivities obtained by the two methods for the cases of smaller pore diameters.

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Section: Introductionmentioning

confidence: 99%

“…Experimental studies of ionic transport in well-defined micropores and membranes were attempted earlier. [4][5][6][7] There are, however, rare reports of precise and well-controlled experiments to quantify ionic transport in well-defined nanopores. 8 Molecular dynamics simulations can often provide interim and complementary answers.…”

Section: Introductionmentioning

confidence: 99%

Structural and Transport Properties of an SPC/E Electrolyte in a Nanopore

2004

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“…Steck and Yeager [15] and Gavach et al [16] carried out one of the early conductivity experiments in perfluorosulfonic acid membranes by means of an ac impedance method. Lack of a definitive measurement of membrane pore sizes and the poor characterization of the membrane structure have made the interpretation of electric conductivity results extremely difficult.…”

Section: Introductionmentioning

confidence: 99%

Anomalous diffusivity and electric conductivity for low concentration electrolytes in nanopores

et al. 2004

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We apply equilibrium and nonequilibrium molecular dynamics simulations to study the dynamic properties of electrolytes in nanopores. The realistic primitive model and the restrictive primitive model widely used in the statistical mechanics of liquid-state theory are applied to model the electrolytes. The electrolytic ions are immersed in water, treated in this work as either a dielectric continuum ignoring the size of solvent molecules or a macroscopic dielectric continuum (polar property) plus neutral soft spheres, and the aqueous electrolyte is put in a confined space. To simulate a condition mimicking closely processes of practical interest and yet maintaining the simulation computationally manageable, we consider an infinitely long and uncharged cylindrical tube. The equilibrium property of the self-diffusion coefficient D and the nonequilibrium property of electric conductivity sigma are computed in terms of electrolyte concentration, particle size, and cylindrical pore radius. The simulation results for the continuum solvent restrictive primitive model and continuum solvent primitive model show normal behavior for D versus pore radius R at ionic concentration 0.1M -i.e., D decreases with decreasing R -display an R independence of D at a certain threshold concentration and undergo an anomalous increase in D with reducing R at a lower value 0.025 M. The mechanism of the anomaly at the ionic concentration 0.025 M was sought for and interpreted in this work to arise from the energetic and entropic factors. Our simulated data of sigma at this same concentration follow the same trend as D. To delve further into the transport properties, we perform simulation studies for the discrete solvent primitive model and make a detailed analysis of the characteristic of the ion radial density functions. Comparison of the latter functions with those in the continuum solvent primitive model sheds light on the simulated diffusion coefficient within the context of discrete solvent primitive model which is about two orders of magnitude less. This difference in D is naturally attributed to the solvent effect. Similar disparities were reported by others for the discrete and continuum restrictive primitive models.

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“…Transport properties of confined electrolytes are of greater technological importance. Conductivity in perfluorosulfonic acid membranes has been measured by ac impedance methods. , The interpretation of results has been hampered by the poor characterization of the membrane structure, and definitive measures of membrane pore sizes are lacking. Westerman-Clark and Anderson measured conductivity of various electrolytes in track-etched mica membranes.…”

Section: Introductionmentioning

confidence: 99%

Diffusivity and Conductivity of a Solvent Primitive Model Electrolyte in a Nanopore by Equilibrium and Nonequilibrium Molecular Dynamics Simulations

2001

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Equilibrium and nonequilibrium molecular dynamics simulations are performed to calculate the diffusion coefficient and electric conductivity of ions in a 0.1 M concentration solution confined in neutral cylindrical pores. The applied model is a solvent primitive model (SPM) in which both ions and solvent molecules are soft core spheres and the polar nature of the solvent is represented implicitly as a background with a given dielectric constant. The simulations are carried out in an isokinetic ensemble, and the system, responsing to an applied electric field, is maintained at constant temperature by a Gaussian thermostat. From equilibrium molecular dynamics, diffusion coefficients of ions and solvent decrease with decreasing pore radius or increasing packing fraction of solvent particles. The conductivity determined by nonequilibrium molecular dynamics shows a similar trend, but the pore-size dependence of conductivity does not have a local maximum as was found in the restricted primitive model in which solvent spheres are absent. Using the Nernst-Einstein relation, the ionic conductivity is also calculated from the equilibrium diffusion coefficient and compared with the conductivity obtained from nonequilibrium simulations. The comparison shows that the Nernst-Einsten relation is not valid only at low solvent packing and in very small pores.

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Conductance Measurements in an Electrolytic Membrane Cell at Elevated Temperatures and Pressures

Cited by 13 publications

References 12 publications

Structural and Transport Properties of an SPC/E Electrolyte in a Nanopore

Structural and Transport Properties of an SPC/E Electrolyte in a Nanopore

Anomalous diffusivity and electric conductivity for low concentration electrolytes in nanopores

Diffusivity and Conductivity of a Solvent Primitive Model Electrolyte in a Nanopore by Equilibrium and Nonequilibrium Molecular Dynamics Simulations

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