Effects of water nanochannel diameter on proton transport in proton‐exchange membranes

Abstract

The effects of water nanochannel diameter on proton transport pathways and properties have been studied using reactive molecular dynamics simulations. The proton distributions and diffusivities have been evaluated using the cylinder model of water domains at various diameters that is the most typical proposed morphological model in proton‐exchange membranes. The proton distributions are analyzed to clarify proton pathways by classifying the water channel into two regions in parallel: an inner channel (free water) and an outer channel (bound water). For all the water contents, the nonmonotonic trends that show a peak at a certain diameter are found to be observed in the proton diffusivity, which is dominated by the proton diffusivity in the free water region and has a strong correlation with the proton distribution that is controlled by the balance between the volume fraction of free water and the surface density of sulfonate groups. The electroosmotic drag coefficients are found to increase monotonically with increasing channel diameter as a result of the increase in the volume fraction of free water. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 867–878

Molecular dynamics of ionic polymer-metal composites

“…It can also serve as a means for obtaining various unknown physical properties of IPMCs, such as the electro-osmotic drag coefficient of water and dielectric constant. These properties are not readily available experimentally, and, to date, they were computed numerically only for bare membranes, without accounting for metal electrodes [28–30]. Finally, our work can provide a bridge between atomistic and continuum considerations.…”

“…Allahyarov and Taylor [23] studied morphological changes of polymeric backbones upon application of electric field with coarse-grained MD, showing the formation of a topology that favours counterions’ transport. Other authors have considered the influence of an external electric field on the membrane structure and mobilities of hydronium counterions [24–28]. Coarse-grained MD simulations of a single ionomer pore with sodium chloride solution and external electric field were used in [29] to compute electro-osmotic drag coefficients, and Mabuchi and Tokumasu [28] performed an analogous analysis for hydronium counterions.…”

“…Other authors have considered the influence of an external electric field on the membrane structure and mobilities of hydronium counterions [24–28]. Coarse-grained MD simulations of a single ionomer pore with sodium chloride solution and external electric field were used in [29] to compute electro-osmotic drag coefficients, and Mabuchi and Tokumasu [28] performed an analogous analysis for hydronium counterions. Additionally, Waters et al [30] investigated the influence of an electric field on ionomers with lithium counterion from the perspective of energy, dielectric properties and transport of counterions.…”

Nafion Ionomer Dispersion in Mixtures of 1‐Propanol and Water Based on the Martini Coarse‐Grained Model

“…Theoretically, many molecular dynamics (MD) simulations of PFSA membranes have been performed to study proton and oxygen transport within the morphology of PFSA membranes and ionomer thin films . Most atomistic simulation studies have primarily focused on the solid state of ionomers in PEMs and CLs with a water volume fraction significantly below 50%.…”

Molecular Dynamics Study of Ion Transport in Polymer Electrolytes of All-Solid-State Li-Ion Batteries

“…Although the types of macromolecules and ions are different in the present study, in our previous studies, we analyzed the ion transport phenomena in polymer electrolyte membranes and polymer thin films with thicknesses of several nanometers in polymer electrolyte fuel cells using MD simulations; further, we analyzed the correlation of the polymer structure with the vehicular ion diffusion [ 17 ], the structural ion diffusion [ 18 , 19 , 20 , 21 ], and the electroosmosis [ 22 ]. Based on these findings, the present study aimed to clarify the effect of nanoscale structural properties on the ion transport properties of the PEO-LiTFSI system and P(2EO-MO)-LiTFSI system.…”