Facilitating Dual-Ion Extraction in Framework Materials through Polyaniline-Mediated Water Blocking and Active Site Augmentation

Framework materials offer abundant ion-intercalation sites; however, their desalination performance is often limited by structural instability and low site utilization due to water molecule cointercalation. Herein, we employ interface engineering by coating the framework material with a compact polymer mediator layer. This approach facilitates ion transport while blocking water molecules and synergistically introduces supplementary active sites. Exemplifying this strategy, a composite material (denoted PCN) is fabricated using NiHCF (a Prussian blue analogue) and polyaniline (PANI). PCN enables efficient dual-ion (Na⁺ and Cl^-) extraction in symmetric flow-electrode capacitive deionization (FCDI) systems for seawater desalination. Mechanistic investigation reveals that the enhanced performance is not primarily attributed to improved electronic/ionic conductivity from PANI. Instead, the PANI layer forms a hydrophobic interface and introduces nitrogen sites, enabling synergistic dual-ion extraction. This compact mediator layer effectively prevents water molecule coinsertion, incorporates nitrogen-rich active sites, and ensures structural stability, thereby enhancing site utilization efficiency. This work demonstrates that modulating material interfaces to suppress H₂O-induced side reactions and augment active site availability advances electrochemical ion extraction for water purification.