Hydrogel Ionotronics with Ultra-Low Impedance and High Signal Fidelity across Broad Frequency and Temperature Ranges

Ionotronics, emerging devices that couple gel ionic conductors and electronic circuits, have shown great promise as stretchable alternatives with multi-functionalities to conventional rigid devices, ranging from energy harvesting to sensing, displaying, and actuation. However, current hydrogel ionotronics' performances are still unsatisfactory: i) upon high alternating current frequency (> 1000 Hz), the ionic conductivity dominates but is rather low and drops further drastically as temperature decreases; ii) upon low frequency (< 1000 Hz), the unstable and high impedance at the electrode/hydrogel interface dominates unfavorably but has been overlooked previously. To remedy these issues, herein, a systematic strategy is proposed by employing a highly ionically-conductive anti-freezing hydrogel and electronically-conductive porous polymer films with high electrical-double-layer capacitance as electrodes to connect the hydrogel and metal leads. The hydrogel has an ultra-high conductivity, while being transparent, stretchable, and easily prepared by one-step photo-gelation. Meanwhile, the conducting polymer electrodes realize a stable and low interfacial impedance and improved voltage tolerance, enabling much higher fidelity of ion-electron signal transduction than using gold electrodes. This strategy can be applied to construct various ionotronics for broad applications, including triboelectric nanogenerators, touch panels, displays, soft robotics, and multifunctional electronics with broad operational frequency and temperature ranges.