Reversal of Salt Concentration Dependencies of Salt and Water Diffusivities in Polymer Electrolyte Membranes

Recent experimental results have shown that transport properties of salt ions and water in charged polymer membranes exhibit an intriguing dependence on salt concentration that is opposite to that seen in electrolyte solutions. Motivated by such observations, in this study we have used atomistic molecular dynamics simulations to investigate the molecular level mechanisms underlying the transport properties of salt solutions in charged polymer membranes. Our results are in qualitative agreement with experimental results and suggest that the mobility of the salt ions is influenced by electrostatic interactions with the charged groups in the polymer membrane. The mobility of water molecules is shown to arise as a consequence of the influence of salt on the hydration characteristics in solution and polymer electrolyte systems.