Impact of GO Chemical Composition on the Performance of Humidity Sensors.

Graphene oxide (GO), a structurally defective 2D carbon nanomaterial, is very promising for relative humidity (RH) sensing applications due to the presence of diverse oxygenated functional groups (OFGs) in its structure. The characteristics of GO, such as flake size, degree of oxidation and exfoliation, permanent structural defects, and chemical composition, directly impact the RH detection performance of GO. In this work, we investigated the performance of resistive RH sensors based on three types of GO, prepared using modifications of the Hummers' method, namely, GO-I, GO-II, and GO-III, having different chemical composition, degree of oxidation, as well as different levels of permanent structural defects (carbon vacancies) at the basal plane. GO-based RH sensors were fabricated by drop-casting GO suspensions onto aluminum interdigitated electrodes thermally evaporated onto glass substrates. Among the three characterized RH sensors, GO-II-based devices showed superior performance, with a sensitivity of 2113 ± 2% compared to 1592 ± 1% for GO-I and 388.1 ± 0.1% for GO-III, respectively. All GO sensors demonstrated rapid response and recovery times (ca. 2 and 3 s). Our results indicate that improved quantities of highly polar OFGs, such as carbonyl and hydroxyl groups, and the associated permanent structural defects in GO-II, significantly improved its RH sensing properties. In addition, all GO-based RH sensors can be operated at only 0.1 V, making them suitable for integration into low-power systems.