Self-Powered Flexible Dual-Mode Humidity Sensor Enabled by Integrated TENG and Visualized Cellulose Nanocrystals

Abstract

Cholesteric liquid crystals are 1D photonic crystals with a helical structure that can selectively reflect light. In this study, we successfully fabricated color cholesteric liquid crystal films using cellulose nanocrystals (CNC) and citric acid (CA) through co-assembly. Due to the reversible swelling and dehydration of its chiral structure, the CA/CNC composite film exhibits reversible structural color responses between green and dark red at relative humidity (RH) of 43%–97%. When used as the friction material for TENG, the CA/CNC composite film exhibits excellent triboelectric performance, with a response time of approximately 22 ms, open-circuit voltage, short-circuit current, charge density and power density of 187.17 V, 7.75 µA, 86.06 nC, and 1.21 W/m2, respectively. CA/CNC-TENG functions not only as a power supply but also incorporates humidity sensing capabilities. When establishing sensing relationships between electrical signals and visual signal RGB values with humidity respectively, its minimum detection limits are 2.4% and 4.9% RH, respectively. Utilizing a convolutional neural network deep learning model to analyze electrical signal and visual signal RGB value data, the average recognition accuracy rates were 95.90% and 97.91% respectively. The integrated CA/CNC-TENG color-visualized humidity sensor may significantly promote the application of TENG in electronic detection devices and environmental monitoring fields.