Bilayer Polyaniline–WO3 Thin-Film Sensors Sensitive to NO2

In this work, a novel bilayer polyaniline–WO3 (PANI–WO3) thin film on the fluorine-doped tin oxide (FTO) glass substrate was prepared by hydrothermal synthesis and in situ chemical oxidative polymerization methods. Until now, no one has ever made attempts to use the PANI–WO3 composite on the FTO glass substrate to detect NO2 gas. The composite showed excellent sensing performance for NO2 detection at an operation temperature of 50 °C and a detection limit of 2 ppm. With regard to the PANI–WO3 hybrid, the response value for NO2 at 30 ppm is 60.19 and is three times higher than that for pure WO3 at 50 °C. Besides, the PANI–WO3 hybrid had excellent stability. The improvement of gas sensing was assigned to the creation of p–n heterojunctions between p-type PANI and n-type WO3, larger specific surface, increase of oxygen vacancies, and a wide conduction channel provided by PANI.