Ultra-high response and selectivity of triethylamine sensor based on NiO/Pd/SnO2 multiple heterojunctions composite

Abstract

Multiple heterojunctions composite may be an effective way to simultaneously improve the selectivity and response of metal oxide semiconductor-based sensors, as well as reduce the working temperature. In this study, the NiO/Pd/SnO₂ composite including PN heterojunction (NiO/SnO₂) and Schottky junction (Pd/SnO₂) was successfully prepared through three steps. The morphology, structure, and chemical state of surface elements were characterized by XRD, SEM, TEM, and XPS. Gas sensing performance displayed that the NiO/Pd/SnO₂ sensor exhibited ultra-high response (1320) and selectivity (>4.1), low detect limit (0.1 ppm) and excellent long-term stability to 100 ppm of TEA at 275°C. Compared with SnO₂ and NiO/SnO₂, Pd/SnO₂ and NiO/Pd/SnO₂ sensors exhibited higher response and lower working temperature. Compared with Pd/SnO₂, the NiO/Pd/SnO₂ sensor exhibited higher selectivity. In addition, the adsorptions of oxygen and TEA on the surface of samples have also been simulated through DFT calculations. Based on the characterization and calculation results, the excellent sensing performance of the NiO/Pd/SnO₂ sensor can be attributed to the multiple heterojunctions and strong activation effect of Pd on oxygen and TEA molecules.