Exceptional Capacitance Enhancement of a Non‐Conducting COF through Potential‐Driven Chemical Modulation by Redox Electrolyte

Abstract Capacitors are the most practical high‐storage and rapid charge‐release devices. The number of ions stored per unit area and their interaction strength with the electrode dictates capacitor‐performance. Microporous materials provide a high storage surface and optimal interactions. Adsorbing electron‐rich and easily polarizable molecules into microporous electrodes is expected to boost Faradaic pseudo‐activity. If such electrode–electrolyte interactions can be made as a potential‐driven reversible process, the resulting capacitors would be adaptable and device‐friendly. A composite covalent organic framework (COF)‐carbon electrode with redox‐active KI is combined in an H 2 SO 4 electrolyte for the first time. This composite electrode benefits from the redox‐functionality of COF and electronic conductivity of carbon, leading to superior capacitative activity. Operando spectro‐electrochemical measurements reveal the existence of multiple polyiodide species, although the I 3 − is the predominantly electroactive species adsorbing on the microporous triazine‐phenol COF electrode. A systematic fabrication of the flexible solid‐state devices using the COF‐redox‐electrolyte reveals a high areal capacitance of 270 ± 11 mF cm −2 and gravimetric capacitance of 57 ± 8 F g −1 . The inclusion of KI in H 2 SO 4 (electrolyte) yields an approximately eight‐fold enhancement in solid‐state gravimetric specific capacitance. The imine‐COF retains 89% of its capacity even after 10 000 cycles.