Pushing the boundaries of electrochemical ion separation for near-identical ions

In recent decades, increasing global population and industrialization have driven interest in the sustainable extraction of valuable resources from water, as well as in water reuse applications. This includes selectively removing undesired ions, such as sodium, or extracting valuable ions, such as lithium, from water. These separations are difficult to achieve due to the high concentrations of competing ions with similar properties, such as charge and size. As a result, separating similar ions, e.g., sodium, potassium, and lithium, is often regarded as the ‘holy grail’ of ion separation. Although selective separation can be achieved with electrochemical desalination technologies, the limited selectivity for ions with the same charge is insufficient for many applications. In this manuscript, we introduce a novel approach for achieving exceptionally high selectivity between two very similar ions, sodium and potassium, by adapting switching times of ion collection. We demonstrate that our method, termed Concentration Dependent Switching (CDS), is effective for sodium and potassium, achieving high removal of one ion while leaving the other in solution. The high removal can be achieved to either of the ions in solution. We highlight its applicability to other challenging separations, including lithium and sodium. The CDS method can be integrated into any cyclically operated deionization technology that exhibits differences in the dynamics of adsorption and desorption of ions. • Concentration Dependent Switching (CDS): high selectivity with cyclic deionization. • CDS achieves high removal of one ion while leaving the other in solution. • CDS is effective for sodium and potassium. • CDS is applicable to other challenging separations, including lithium and sodium. • CDS can be integrated into any cyclically operated deionization technology.