Ultrahigh humidity sensitivity of graphene oxide combined with Ag nanoparticles

Novel capacitive-type humidity sensors with ultrahigh sensitivity based on graphene oxide (GO) combined with Ag nanoparticles (AgNPs) in different concentrations are reported in this study. Various characterization techniques such as transmission electron microscopy (TEM), X-ray diffraction (XRD), water contact angles, and Fourier transform infrared spectroscopy (FTIR) were used to verify the composite formation. The best performance was shown by the GO/Ag (2 wt%) composite-based sensors, with a sensitivity of 25 809 pF/% RH in the humidity range from 11% RH to 97% RH and 328 pF/% RH in the humidity range from 11% to 33% RH, which was 100 times larger than that of the previous humidity sensor, especially at low humidity levels (<33% RH). The Schottky junction theory and complex impedance spectroscopy were employed to understand the underlying sensing mechanisms of the GO/Ag composite towards humidity. The GO/Ag composite was proven to be an excellent candidate for the construction of ultrahigh-sensitivity humidity sensors for various applications.