Redox-responsive ionic covalent organic framework films for hydroxide ion transport and tunable mechanical properties

Hydroxide ion conduction is essential for advanced energy conversion and storage technologies. We report a flexible and mechanically robust viologen-based two-dimensional ionic covalent organic framework (iCOF) film, TG-V²⁺ synthesized via a green, catalyst-free sol-gel process under ambient conditions. The film exhibits strong alkaline stability and achieves a hydroxide ion conductivity of 9 × 10^-3 S cm^-1 at 100 °C. The redox-active viologen units enable electrochromic switching and a four-fold enhancement in mechanical stiffness (Young's modulus = 4.5 GPa). The combined ion-conducting and redox-responsive properties of the TG-V²⁺ COF film provide a promising proof-of-concept platform for multifunctional ionic COF membranes and related electrochemical applications.