Electrochemically Controlled Deposition of Oriented Fluorinated Covalent Organic Framework Films for Selective Electrochemical Sensing

Covalent organic frameworks (COFs) are crystalline, porous materials with tunable structures and significant potential for applications, such as molecular separation and sensing. However, the fabrication of large-area, uniform, and defect-free COF films with controlled thickness and high crystallinity remains a major challenge. This study presents a rapid, scalable, two-step strategy for fabricating oriented crystalline fluorinated COF (F-COF) films. The process combines electrochemical deposition of an amorphous intermediate film induced by electrogenerated acid with subsequent annealing with acid vapor to achieve solid-state crystallization. Under mild conditions, this method produces free-standing, micrometer-thick F-COF films with crystallinity over centimeter-scale areas with a significantly shortened reaction time. The resulting F-COF films exhibit high crystallinity and orientation, thereby enhancing electron transport and enabling selective molecular sieving. These films can effectively discriminate small molecules such as alkylamines, even in the presence of interfering metal ions, highlighting their potential as contamination-resistant electrochemical sensors. The proposed approach provides a practical methodology for fabricating functional F-COF films and establishes a model for their electrochemical application.