Direct Current-Powered High-Performance Ionic Hydrogel Strain Sensor Based on Electrochemical Redox Reaction.

Ionic hydrogel-based resistance strain sensors (IRS-sensors) powered by direct current (dc) enable various wearable applications. However, the unclear signal transmission mechanism causes significant difficulty to solve the problem of their weak detection ability for subtle strain changes. Here, we have conducted a combined theoretical and experimental study to demonstrate that the signal transmission of dc-powered IRS-sensors is determined by the electrochemical redox process. The slow H+ reduction rate and chemical component change within the hydrogel account for their low sensitivity and signal-to-noise ratio (SNR). To address such a challenge, we have introduced Cu2+ into the hydrogels to enhance the cathodic reduction rate and the chemical stability of the IRS-sensors. The as-prepared IRS-sensors show high sensitivity, ultrahigh SNR, and excellent sensing reliability. Besides the inherent ultrawide sensing range (>1500%), the IRS-sensor can also provide recognizable electrical responses to the incredibly small strain (0.005%), which is 2 orders of magnitude lower than previous ones. They demonstrate precise and reliable monitoring for full-range human activities. This new strategy can be easily extended to other ionic hydrogels and electrodes as well as self-driving electrochemical electrodes for the fabrication of various high-performance self-powered IRS-sensors.