Perspective: Morphology and ion transport in ion-containing polymers from multiscale modeling and simulations

Abstract

Ion-containing polymers are soft materials composed of polymeric chains and mobile ions. Over the past several decades they have been the focus of considerable research and development for their use as the electrolyte in energy conversion and storage devices. Recent and significant results obtained from multiscale simulations and modeling for proton exchange membranes (PEMs), anion exchange membranes (AEMs), and polymerized ionic liquids (polyILs) are reviewed. The interplay of morphology and ion transport is emphasized. We discuss the influences of polymer architecture, tethered ionic groups, rigidity of the backbone, solvents, and additives on both morphology and ion transport in terms of specific interactions. Novel design strategies are highlighted including precisely controlling molecular conformations to design highly ordered morphologies; tuning the solvation structure of hydronium or hydroxide ions in hydrated ion exchange membranes; turning negative ion-ion correlations to positive correlations to improve ionic conductivity in polyILs; and balancing the strength of noncovalent interactions. The design of single-ion conductors, well-defined supramolecular architectures with enhanced one-dimensional ion transport, and the understanding of the hierarchy of the specific interactions continue as challenges but promising goals for future research.

Branched Poly(arylene ether ketone sulfone)s with Ultradensely Sulfonated Branched Centers for Proton Exchange Membranes: Effect of the Positions of the Sulfonic Acid Groups

“…The generally accepted mechanisms of proton conduction in PEMs are mainly vehicle and Grotthuss (or hopping) mechanisms, both relying on water molecules as carriers. , Hence, adequate water absorption of PEMs facilitates proton transport, whereas excessive water content within membranes induces significant dimensional variations, thereby impairing the mechanical performance and the practical application capability. , The WU of B- x -SPAEKS and B-10-SPAEKS-30 membranes as a function of temperature is illustrated in Figure a, in which the WU of B- x -SPAEKS displayed an upward trend with the increase of IEC and temperature. However, the WU of the B-10-SPAEKS membrane was considerably lower than that of the B-10-SPAEKS-30 membrane over the whole temperature range, despite the IEC values of both being nearly identical.…”

Polymerized and Colloidal Ionic Liquids─Syntheses and Applications

“…Polymerized ionic liquids composed of polymeric chains and corresponding counterions, as ideal ion-containing polymers having an ion transport ability, have sparked increasing interest for several decades due to their promising applications in conductive electrolytes and ion exchange membranes. 476,477 3.6.1. Dynamics.…”

“…Ion transport directly contributes to charge transfer in an electric field, forming an ionically conductive pathway, and is an equally important physical property compared to electronic conductivity. Polymerized ionic liquids composed of polymeric chains and corresponding counterions, as ideal ion-containing polymers having an ion transport ability, have sparked increasing interest for several decades due to their promising applications in conductive electrolytes and ion exchange membranes. , …”

Electrode Separators for the Next-Generation Alkaline Water Electrolyzers

“…When soaked in water, the ionic groups dissociate into the immobile cationic groups on the polymer and mobile hydroxide ions that support the ionic current between the electrodes. Like perfluorosulfonic acid membranes, many AEM chemistries have been reported to develop a phase separated nanomorphology upon hydration, although structure–property relationships depend on a large number of parameters and are not yet fully understood . The third approach (Figure c) makes use of ion-solvating polymer membranes that contain polar or ionizable groups, such as benzimidazoles or imidazoles, that promote excessive uptake of aqueous alkali metal hydroxide solutions to form a homogeneous morphology without distinct phase separation. − The term ion-solvating polymer electrolyte was introduced in the context of nonaqueous electrolyte chemistries based on mixtures of, e.g., poly­(ethylene oxide) and lithium salts but has been adapted by the alkaline polymer electrolyte community for polymer systems doped with aqueous KOH although excess water needs to be present to fully solvate the dissociated ions …”