Microstructure Related Synergic Sensoring Mechanism in Graphene Oxide Humidity Sensor

Graphene oxide (GO) is a good candidate for high-performance humidity sensors with high responsitivity and rapid response. The GO sensoring mechanism is highly concerned and still not yet well understood. In this study, a systematic examination of GO capacitive humidity sensors was performed, revealing GO sensors' excellent sensitivity properties with two orders of capacitance change (within a relative humidity range of 12-97 RH%) and sub-0.1 s (tau(95)) response at room temperature being observed. A Fourier transform infrared technique was used to study the structural characteristics of GO films under both steady and transient humidity states. Interaction of water molecules with the functional groups in GO was detected, which induced evident changes of the GO structure and directly related to the sensoring processes. Free state liquid water was found to play an important role in the sensoring processes. A synergistic sensoring mechanism is suggested: functional groups work to reserve water and produce a larger layer space for better water transportation, while regions without functional groups work as effective channels for water transportation.