Flexible wearable and self-powered humidity sensor based on moisture-dependent voltage generation

• Development of CoCl 2 @NWF self-powered humidity sensor. • The novel humidity sensor is characterized with significant voltage output (~200 mV) with constant humidity of RH 98%. • The humidity sensor could be used to monitor human breath. With the rapid development of technology, researchers have been paying a lot of attention to personal health wearable electronics products. And environmentally friendly and renewable cellulose-based materials have become a research hotspot. In this work, the porous pure cotton non-woven fabric (NWF) was used as the backing material and modified by different concentration of CoCl 2 solutions in order to obtain the CoCl 2 @NWF composite film with moisture-sensitive properties. Switching tests under different relative humidity levels showed that the CoCl 2 @NWF composite film would have visible discoloration. The humidity sensor obtained by simple pasting not only shows a maximum response value of more than 200 mV output voltage under 98% relative humidity (RH), but also a good cyclic performance. In addition, due to the unique characteristics of non-woven materials, the sensor also exhibits excellent resistance to bending and durability. Finally, we also explored the humidity monitoring of this sensor, which showed an excellent response performance to human respiration; thus, indicating that our sensor exhibits great potential in practical applications.