Affinity‐Mediated Percolation Enables Selective Transport of Chemically Similar Divalent Cations in Mixed‐Matrix Membranes

Ion transport in membranes is typically governed by electrostatic exclusion and steric confinement, which fundamentally limit discrimination between ions of identical charge and comparable radii. Here, we demonstrate that intrinsic solid‐state intercalation affinity can be translated into membrane‐scale divalent ion selectivity. To realize this concept, we engineered mixed‐matrix membranes by embedding Chevrel‐phase (Ni 2 Mo 6 S 8 ) particles within a crosslinked anion‐exchange polymer to form a continuous affinity‐mediated percolation pathway that preferentially conducts Ni 2+ over Mg 2+ under electrodialysis. Electrochemical analysis reveals that Ni selectivity originates from rapid interfacial partitioning into the Chevrel lattice, while overall flux is governed by diffusive transport through the dispersed solid‐state network. The membrane maintains Ni selectivity under strongly Mg‐rich conditions (Ni:Mg = 1:66) and achieves separation factors exceeding 35 000 in real laterite leachate. These findings define affinity‐mediated intercalation–percolation as a generalizable materials design principle for discriminating chemically similar divalent cations beyond the limits of conventional membrane selectivity mechanisms.