Redox-Driven Framework Expansion in Viologen COFs for Programmable Electrochemical Actuation

Abstract Electrochemically driven ionic actuators operating at low voltages are promising for soft robotics, haptic interfaces, and adaptive systems. Yet, achieving fast response, large strain, long-term durability, and discrete stepwise actuation remains challenging. Here, we report a high-performance ion-driven actuator based on a viologen-based cationic covalent organic framework (V-COF), which integrates the ordered porosity and mechanical robustness of COFs with the rapid and reversible redox chemistry of viologen. The incorporation redox-active centers within the COF backbone enables redox-state-dependent lattice expansion and counterion diffusion under a small electrical bias, thereby translating molecular redox switching into controllable electrochemical actuation. The actuator exhibits a peak-to-peak bending strain of 1.86%, fast response time of 2.8 s, and cycling stability of 10,000 cycles with negligible degradation. Ex-situ and in-situ electrochemical analyses reveal that actuation is driven by reversible viologen redox reactions coupled with counterion diffusion through the ionically charged COF framework. This work establishes redox-active ionic COFs as a new class of actuator materials that bridge molecular-scale charge transfer and macroscopic motion, offering a new molecular design strategy for durable, low-voltage electrochemical actuation in soft robotic and smart-system applications.