Selectivity mechanisms of ion intercalation in Prussian blue analogs

Prussian blue analogs (PBAs) have demonstrated remarkable capability for facile, reversible, and selective ion transport. However, many details behind the mechanisms underlying their ion selectivity are unclear, hindering rational design of their composition and structure. Ion selectivity is determined by the thermodynamic binding energy and transport kinetic barriers; therefore, elucidation of ion transport pathways and storage sites is critical to uncovering the origins of a material’s ion selectivity. Here, using the model PBA copper hexacyanoferrate (CuHCFe) with percolating vacancies, we investigate the intercalation of eight technologically and naturally prominent ions and determine an overall sequence of selectivity. We reveal strong correlation between the redox center, ion storage site, and intercalating ion identity, owing to the positioning and symmetry of vacancies in the material. Based on the selectivity property, we demonstrate Li purification with CuHCFe. Our findings offer deeper understanding for identifying and harnessing chemical “handles” to enhance separation performance.