Experimental and theoretical investigation of palladium-doped zinc oxide nanorods for NO2 gas sensor

The high concentration of nitrogen dioxide (NO2) gets it one of the most popular and harmful air pollutants. This work examines the NO2 gas sensing properties of palladium-doped zinc oxide (Pd-ZnO) nanorods. The Pd-ZnO nanorods were synthesized by chemical hydrothermal method with different Pd doping concentrations (0-1 wt%). The Pd-ZnO nanorods were characterized by XRD, FESEM, and XPS for their structural and morphological properties, respectively. The ZnO nanostructures show hexagonal structures, and XRD and XPS results confirmed the doping of Pd on ZnO nanostructures. The Pd (1 wt%)-ZnO nanorods-based sensor shows high response of 22.1 with response/recovery time of 67/118 s toward 100 ppm NO2, while it exhibits a response of 7 with response/recovery times of 80/145 s for 1 ppm NO2, at 200 degrees C. The sensor is observed very selective for NO2 compared to other gases like carbon monoxide (CO), ammonia (NH3), and hydrogen (H-2). The sensor has strong stability for a longer time (35 days) in a dry and humid (RH 60%) environment. The mechanism of gas sensors is further explained by the Crowell-Sze model in Finite-Difference Time-Domain (FDTD) simulation using COMSOL Multiphysics using drift Diffusion-Poisson equations to simulate the electric potential distribution in the nanorods during the gas sensing.