Specific Ion Selectivity in Sulfonated Polystyrene Membranes Near the Percolation Threshold

# Data for: Specific Ion Selectivity in Sulfonated Polystyrene Membranes Near the Percolation Threshold --- ## Associated publication **Title:** Specific Ion Selectivity in Sulfonated Polystyrene Membranes Near the Percolation Threshold **Authors:** Yuxuan Huang†,¹ Marshall C. Tekell†,² Jingchao Qin,² Sanat K. Kumar,*,² and Ngai Yin Yip*,¹,³ † These authors contributed equally.\* Corresponding authors. **Affiliations:**1. Department of Earth and Environmental Engineering, Columbia University, New York, New York 10027-6623, United States2. Department of Chemical Engineering, Columbia University, New York, New York 10027-6623, United States3. Columbia Water Center, Columbia University, New York, New York 10027-6623, United States **Journal:** Nature Chemical Engineering **DOI (article):** `[In Revision]`**DOI (this dataset):** `[10.5281/zenodo.20975856]` --- ## Abstract Engineering selective transport between ions of the same valence is critical for separations in water, energy, and the environment, but remains technically challenging for ion-exchange membranes (IEMs). In this study, we hypothesize that cation exchange membranes with sufficiently water-poor matrices can leverage differences in the ion dehydration free energy, −G_hyd, to enhance selectivity between monovalent alkali metal cations. Thin films of sulfonated polystyrene random copolymers with controlled sulfonation levels were fabricated to tune membrane hydration. Mixed-cation electrodialysis experiments showed increased selectivity for K⁺ over Li⁺ as membrane hydration decreased, while mobility ratios remained unchanged—indicating that preferential sorption of K⁺, with lower −G_hyd, governs the preferential transport. Selectivities up to 3.1 were achieved, surpassing commercial IEM benchmarks. However, excessive dehydration below a percolation threshold led to loss of ion transport due to disruption of ion cluster connectivity. These findings provide key structure-property insights into partial ion dehydration and hydration-dependent percolation, informing new design strategies for IEMs with enhanced specific ion selectivity. --- ## Repository structure ```.├── README.md ← this file├── NMR Data/ ← H-NMR data of random copolymers│ └── ...└── Scattering Data/ ← WAXS and MAXS data of dry and hydrated films └── ...```