Cyano‐Triggered Strong Anion‐π Interactions: Unlocking Anion–Cation Adsorption Bifunction

Abstract

ABSTRACT Due to the inherent differences in anion and cation adsorption mechanisms, designing a single Faradaic material that functions as an efficient symmetric capacitive deionization (CDI) electrode for desalination poses a significant challenge. Herein, by employing a simple n‐type azabenzene compound, hexaazatrinaphthalene (HATN), as a template, we introduce strong electron‐withdrawing cyano (C≡N) groups to drastically reduce its surface electron density, constructing an electron‐deficient system with a positive surface potential and a highly positive permanent quadrupole moment ( Q zz ), denoted as HCNAP. This unique electronic structure triggers anion‐π interactions and consequently enables anion adsorption. Meanwhile, the C═N and C≡N groups on the HCNAP skeleton maintain the function of cation adsorption. As a proof of concept, the symmetric CDI device fabricated with HCNAP exhibits outstanding desalination performance in a 500 mg L −1 NaCl solution, achieving a salt adsorption capacity of 53.88 mg g −1 and a removal rate of 10.1 mg g −1 min −1 . Theoretical calculations and experimental results clearly reveal the adsorption mechanism of Na + and Cl − . Besides, HCNAP presents favorable adsorption toward three additional cations and anions. This innovative strategy establishes a new paradigm for constructing bifunctional Faradaic electrodes for highly efficient desalination.