Molecular Dynamics Study of Magnesium and Sodium Ion Transport in a Sulfonated Cation Exchange Membrane

This study focused on understanding the diffusion of sodium and magnesium ions in a sulfonated poly-(ether ether ketone) cation exchange membrane as a function of water content and ionic composition. For that aim, molecular dynamics simulations were used to represent a conductive environment involving the polymer's functional chains, water molecules and ions. Mean squared displacement and self-diffusion coefficients revealed subdiffusive behavior, indicating that ion mobility is limited by the membrane's structure, leading to slower-than-normal diffusion rates. Magnesium ions exhibited self-diffusion coefficients 2 orders of magnitude lower than sodium ions and established stronger interactions with membrane functional groups than monovalent ions, affecting properties like porosity and tortuosity. The water content and polymer structure were critical in conforming hydrophilic networks that support ion mobility and diffusion. This research gives valuable insights into the transport of divalent ions through cation exchange membranes, which is relevant to applications such as electrodialysis and reverse electrodialysis.