Interface Barrier Layers to Suppress Side Redox Reactions of High‐Voltage Hydrogel Iontronics

Abstract Soft hydrogel iontronic devices, utilizing the assumed non‐Faradaic exchange of ions and electrons at the metal‐hydrogel interfaces, have been demonstrated with advantages of high stretchability, transparency, and biocompatibility. Yet, in real situation under high voltage, Faradaic reaction is inevitable, which can breakdown the device and lead to the low durability. Herein, the Faradaic breakdown behaviors of hydrogel iontronic devices under high AC voltage are systematically studied. Side reactions including electrode corrosion and water electrolysis are confirmed in the electrical double layer. Interface barrier layers are proposed to eliminate this issue. It is found that acetylene black (ACET) as modification layer can achieve the best performances, providing effective protection while maintaining the electrical performances. By leveraging ACET‐modified electrodes, long‐term durable iontronics, including electroluminescent devices and high‐output triboelectric nanogenerators, are successfully demonstrated. This work can provide insightful strategies for developing practical hydrogel iontronic devices.