High performance and cost-effective flexible humidity sensor based on eco-friendly and biodegradable nanocellulose

A cost-effective flexible humidity sensor using eco-friendly and biodegradable nanocellulose (NC) as humidity sensing material has been proposed in this paper. The flexible humidity sensor was prepared by depositing NC films on the flexible interdigitated electrodes (IDE). The material properties of the synthesized NC were analyzed by transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), respectively. At the excitation frequency of 1 V and 100 Hz, the sensor achieved up to five orders of magnitude changes in impedance and capacitance over 11.3% to 97.3% humidity range. The flexibility test results indicated this sensor was able to maintain excellent humidity response ability even in bending state. The response and recovery time of the sensor was about 48 s and 12 s, respectively. Meanwhile, it was found that the sensor possessed good repeatability during multiple measurements. Further, the underlying humidity sensing mechanism of NC material was systematically analyzed and discussed using complex impedance spectroscopy (CIS) method. This work demonstrates that NC is promising candidate material for realizing high responsive, cost-effective and eco-friendly flexible humidity sensor.