New Methodology for Characterizing Ion Permeability and Selectivity of Ion-Exchange Membranes

Ion-exchange membranes (IEMs) are critical to electrochemical ion-separation technologies for environmental and energy applications. Although advancements in separation performance have been frequently reported, significant challenges in evaluating mixed-salt IEM performance under electro-driven conditions remain largely overlooked. Here, we present a new method for the rapid and standardized characterization of ion transport properties for IEMs in mixed-salt systems. Using a modified Goldman-Hodgkin-Katz equation, we demonstrate that individual ion permeability can be obtained from IEM conductance measurements with mixed-salt linear sweep voltammetry experiments. Under low-current conditions, the ion permeability ratio can be converted into different metrics for quantification of ion–ion selectivity including current-based and flux-based selectivity. Our findings also reveal substantial differences between ion transport properties of IEMs under single-salt and mixed-salt conditions, highlighting the critical role of competing ions in transport experiments. Overall, this new approach provides an efficient framework to evaluate IEM performance in environmentally relevant conditions, facilitating cross-membrane performance comparison and establishing the foundation to elucidate the structure-property-performance relationships for IEMs in mixed-salt systems.