Molecular analysis of proton and water transport in the nanostructure of polymer electrolyte membrane

We have performed an atomistic analysis of the vehicular transport of hydronium ions and water molecules in the nanostructure of hydrated Nafion membrane using classical molecular dynamics simulations with a model of Nafion membrane based on DREIDING force field, which is newly modified and validated by comparing the density, water diffusivity, and morphology of the membrane with those obtained experimentally. In addition to determination of radial distribution function of solvent molecules vicinity of sulfonate groups as a function of hydration level, we have also calculated mean residence time of solvent molecules in the solvation shells which were classified into three types, overlapped shell, single shell, and second solvation shell. The mean residence time of solvent molecules explicitly showed different behaviors in each region, and they provided insights into the correlation between the nanoscopic structure of ion clusters and the dynamics of hydronium ions and water molecules in the membrane.