Publications

Water absorption plays a key role in the performance of polymeric anion exchange membranes. It influences important properties such as ionic conductivity and mechanical strength and alters their performance as solid electrolytes in hydrogen electrochemical devices for energy conversion. However, computational approaches that address the relationship between the polymer design and the absorption process are scarce. In this work, we introduce a simple thermodynamic model to predict the water absorption isotherms of polyelectrolyte membranes in contact with a water vapor reservoir that incorporates the specific chemical design of the polymers. The model accurately predicts the water content and macrostructural properties of polynorbornene membranes as a function of the water activity and successfully captures the effect of various polymer design parameters. The energy of pairwise attractive interactions predicted by our model provides a means to interpret the absorption process at the molecular level. The model also reveals the most significant favorable and unfavorable contributions to the free energy and indicates that their balance is solely governed by the water volume fraction, regardless of the polymer design. This universal behavior leads to important implications in the search for better ion exchange membranes.

Understanding the structure-property relationships governing ion transport in hydrated polyelectrolytes is crucial for the design and optimization of electrochemical devices. By combining experiments and simulation, the influence of polymer chain segmental dynamics and water concentration on ion transport in polyelectrolytes is investigated. The segmental dynamics of a series of thermally crosslinked poly(2-vinylpyridine)-based polyelectrolytes have been systematically modified by varying the degree of crosslinking. The experimental and simulation results indicate that segmental dynamics have a limited influence on ion transport in hydrated polyelectrolytes. Instead, ion transport is primarily dictated by the water concentration within the hydrated polyelectrolytes. Both crosslinked and non-crosslinked polyelectrolytes exhibit similar conductivities when normalized for water concentrations. Compared to the widely used crosslinking method with alkyl-diamine linkage, the thermal crosslinking approach employed here not only provides an ideal platform for studying structure-transport relationships in polyelectrolytes but also offers a promising strategy to enhance their mechanical properties by preserving backbone rigidity without sacrificing ionic conductivity.