Transport Phenomena of Solutes in Dense Polymer Membranes

Abstract

Ion exchange membranes (IEMs) are indispensable materials with diverse applications in energy and environmental technologies, such as fuel cells, water desalination, water purification, and electrochemical CO2 reduction systems. IEMs facilitate selective ion transport while maintaining charge balance, minimizing undesired crossover of species, and ensuring efficient separation processes. However, the development of IEMs is hindered by several challenges. A key issue is the trade-off between ionic conductivity and selectivity, where enhancing one often compromises the other. Additionally, the undesired crossover of reactants or byproducts can significantly diminish system efficiency and product purity. Compounding these issues is an incomplete understanding of the structure-property relationships that govern membrane behavior, limiting the ability to design tailored membranes for specific applications. To address these challenges, this study investigates (1) single and co-transport solute behavior across various IEMs, (2) solute transport characteristics in membranes with comparable water volume fractions, and (3) the impact of different polymer structures on solute transport. In anion exchange membranes (AEMs), we observed that the co-permeation of alcohol and carboxylate ions decreases, while the co-permeation of two carboxylates exhibits competitive transport. However, the water volume fraction generally has the most significant influence on transport behavior. Different monomers impart distinct physicochemical properties to the membrane, substantially affecting solute transport.