Understanding charge transfer processes between graphene and functional materials is crucial from the perspectives of fundamental sciences and potential applications, including electronic devices, photonic devices, and sensors. In this study, we present the charge transfer behavior of graphene and amine-rich polyethyleneimine (PEI) upon CO₂ exposure, which was significantly improved after introduction of hygroscopic polyethylene glycol (PEG) in humid air. By blending PEI and PEG, the number of protonated amine groups in PEI was remarkably increased in the presence of water molecules, leading to a strong electron doping effect on graphene. The presence of CO₂ gas resulted in a large change in the resistance of PEI/PEG-co-functionalized graphene because of the dramatic reduction of said doping effect, reaching a maximum sensitivity of 32% at 5, 000 ppm CO₂ and an applied bias of 0.1 V in air with 60% relative humidity at room temperature. This charge transfer correlation will facilitate the development of portable graphene-based sensors for real-time gas detection and the extension of the applications of graphene-based electronic and photonic devices.

The corrosion of metals can be induced by different environmental and operational conditions, and protecting metals from corrosion is a serious concern in many applications. The development of new materials and/or technologies to improve the efficiency of anti-corrosion coatings has attracted renewed interest. In this study, we develop a protective coating composed of a bilayer structure of reduced graphene oxide (RGO)/graphene oxide (GO) applied to Cu plates by spray-coating and subsequent annealing. The annealing of the GO/Cu plates at 120 ℃ produces a bilayer structure of RGO/GO by the partial reduction of the spray-coated GO layer. This induces superior corrosion resistance and adhesion strength compared to those of GO/Cu and RGO/Cu plates because of the hydrophobic nature of the RGO surface exposed to the surroundings and the formation of Cu-O bonds with the O-based functional groups of GO. This approach provides a viable and scalable route for using graphene coatings to protect metal surfaces from corrosion.