Graphene/polyaniline (Pani) nanocomposites (G/Pani) were prepared by in situ chemical oxidative polymerization using different (0–30 wt%) of graphene. According to the characterization, the presence of graphene in Pani matrix reduced the density of surface states and increased the defect density. The partial protonation of Pani and different wt% of graphene showed significant effect on CO2 gas sensing at room temperature and high humidity (ca. 90%). All prepared samples showed dynamic response and rapid recovery time to different concentrations of CO2. The nanocomposite with 20 wt% of graphene exhibited better protonation degree, sensitivity and reversibility to other samples. The sensor responded to 0.5 vol% CO2 gas three times bigger than Pani. The excellent long-term stability (about 18% less than the initial experiment) was obtained for the sensor based on G/Pani after 1 year, which makes it a potential candidate for application in CO2 gas sensor.
