Ultrastrong, Highly Conductive and Capacitive Hydrogel Electrode for Electron-ion Transduction

Abstract

Electron-ion transduction is the cornerstone for electronic devices interfacing with biological organisms and promoting emerging ionotronic devices, ranging from basic electronic elements to wearable electronics and energy harvesting devices. However, with commonly used metal electrodes, the electron-ion transduction suffers from high impedance, signal distortion and poor voltage tolerance. Surface modification with conductive porous materials could partially remedy these issues but is inevitably accompanied by weak interfacial adhesion and mechanical weakness. Therefore, freestanding electrodes integrating high mechanical and electrical properties are highly demanded. Herein, a general strategy is discovered to ameliorate these issues by introducing a conducting polymer (CP) hydrogel electrode of ultrahigh strength (~30 MPa) and conductivity (up to ~1200 S cm−1) with a capacitive behavior. These features are derived from the conductive nanoporous matrix with π-π interactions as both crosslinking sites and electron-transfer pathways, through surface gelation coupled with secondary-doping and densification. This strategy significantly decreased the low-frequency impedance and improved the signal fidelity, without affecting its high-frequency response. Furthermore, excellent biocompatibility, multifunctionality, and heart pacing upon ultra-low voltage (60% reduction) have also been demonstrated, showing the great potential of this CP material for bioelectronic applications and various human-machine interfaces.