Synergistic humidity-responsive mechanical motion and proton conductivity in a cationic covalent organic framework

The development of flexible, humidity-responsive actuator materials is critical for advanced sensors and electronic systems. Current fabrication methods are complex and harsh. We present a novel approach that uses one-step synthesis at room temperature to prepare a self-standing cationic covalent organic framework (TG-DFP COF) film. Because hydrogen bonding and ionic surface coverage are present throughout the COF network, this material facilitates the rapid adsorption and desorption of water vapor, leading to an ultrafast actuating response rate of less than 1 s. At high humidity, the entrapped water molecules enhance the hydrogen-bonding interactions, leading to an impressive proton conductivity of 2.8 mS cm⁻¹, which is among the highest reported for cationic COFs. This study demonstrates a unique 2D-ordered system that combines high proton conductivity and shape-changing ability with remarkable stability.