Capacitive flexible humidity sensor based on GOQD/CNC composites

In response to the urgent demand for highly sensitive, flexible, and reliable humidity sensors in fields such as environmental monitoring, industrial control, and biomedicine, a humidity sensor with graphene oxide quantum dots (GOQD) and cellulose nanocrystals (CNC) composites as the humidity-sensitive materials and a flexible polyimide-based interdigitated electrode as the transducer is developed in this study. The experimental results show that the capacitive response of GOQD/CNC composites to humidity is greatly improved with a sensitivity of 1439.6 pF/%RH, which is approximately 3 times higher than that of pure GOQD, and more than 21 times higher than that of pure CNC. This significant enhancement is attributed to the synergistic effect between the GOQDs and the CNC, where the addition of the CNC allows for smaller sized GOQDs to adhere to the surface, which mitigates the aggregation of the GOQDs to a certain extent and increases the contact area of the composite with water molecules, thus increasing the sensitivity of the sensors to changes in humidity considerably. Moreover, the GOQD/CNC-based humidity sensor also exhibits good stability, small hysteresis, rapid response/recovery times, and excellent repeatability. This research provides a new approach for the design of high-performance flexible humidity sensors.