Ultrasensitive ammonia sensor with excellent humidity resistance based on PANI/SnS₂ heterojunction

The analysis of human exhaled gas is crucial for early and noninvasive diagnosis. However, the complex composition and high-humidity of exhaled gas pose significant challenges to the application of gas sensors. This research focuses on the development of a chemiresistive ammonia sensor based on the polyaniline/tin disulfide (PANI/SnS₂) heterojunction, which is fabricated by hydrothermal and in-situ polymerization techniques. The sensor demonstrates significantly enhanced gas sensing capabilities manifested by increased responsiveness, improved selectivity, and stability for detecting 0.5-100 ppm ammonia at ambient temperature. Notably, the sensor exhibits a marked enhancement in response at high humidity levels. When exposed to 30 ppm of ammonia, the sensor's response value increases by 167 % at a relative humidity (RH) of 80 %, compared to 128 % at 50 % RH. This significant improvement can be attributed to the unique interaction between water molecules and the sensor material, which enhances the overall charge transfer processes at the PANI/SnS₂ interface. Furthermore, in-situ techniques as well as theoretical calculations are utilized to gain insight into the sensitization mechanism. The proposed PANI/SnS₂ heterojunction sensor shows great promise for applications in high-humidity environment at ambient temperature.