Porous and conductive cellulose nanofiber/carbon nanotube foam as a humidity sensor with high sensitivity

In this study, we developed a humidity sensor with high sensitivity based on cellulose nanofiber/carbon nanotube (CNF/CNT) hybrid foam. The porous structure of the foam not only provides more contact interface for water molecules adsorption, but also tunes the conductivity of the CCF closed to the point where the sensor is most sensitive to the change in humidity. With this porous structural design, the obtained foam sensor shows a high humidity sensitivity of 87.3% (ΔI/I0, and the response limit is 100%), excellent linearity (R2 = 0.996) within the humidity range from 29 to 95% relative humidity (RH), and good long-time stability (more than two months). Furthermore, the water vapor adsorption behavior of the CNF/CNT foam sensor can be well described by the pseudo-first-order kinetic model. Finally, a simple humidity measuring device based on the CNF/CNT foam is presented, which can find good applications for human breath and fingertip humidity monitoring.