Facile fabrication of high sensitivity cellulose nanocrystals based QCM humidity sensors with asymmetric electrode structure

In this paper, a new approach to enhance the humidity sensitivity of quartz crystal microbalance (QCM) humidity sensor was proposed. By the asymmetric treatment of QCM electrode, the as-fabricated QCM humidity sensor produces an additional frequency shifts associated with the change of dielectric constant of sensitive material besides mass sensitivity. Renewable cellulose nanocrystals (CNCs) as humidity sensing material was deposited on the sensing electrode of QCM. The material characteristics of the synthesized CNCs were examined by TEM, AFM, FTIR and XRD, respectively. The humidity sensing performances of CNCs based QCM humidity sensor, including humidity sensitivity, stability, humidity hysteresis and dynamic response and recovery, were comprehensively studied by using an oscillating circuit method. The results proved that the humidity sensitivity of CNCs based QCM humidity sensor can be effectively enhanced by the asymmetric treatment of QCM electrode structure. Further, the underlying sensitivity enhancement mechanism was analyzed and discussed using an equivalent circuit analysis method. This work highlights that QCM transducer with an asymmetric sensitive electrode structure is a promising approach to improve the humidity sensitivity, and CNCs is also a promising material for humidity sensing.