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 <i>in situ</i> 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.