The Sensitizing Effect of Enhanced NO₂ Gas Sensing at Near-Room Temperature Using Pd-Decorated VO₂ Nanowires

Modification of nanostructures using metal nanoparticles is an efficient strategy for enhancing the performance of gas sensing. In this paper, a VO₂@Pd nanowires gas sensor was synthesized using a combination of hydrothermal and annealing methods. The content of Pd in the as-prepared products was successfully controlled by adjusting the reaction parameters. The morphology and formation mechanism of VO₂ nanostructures were systematically evaluated. The response value of VO₂@Pd nanowires is 31.94 towards 5 ppm of NO₂, which is about 38.75% higher than that of pristine VO₂ at a relatively low temperature of 50°C. Furthermore, the sensor exhibits good selectivity, excellent response/recovery time, and superior stability towards NO₂. The significant enhancement of NO₂ sensing performance could be attributed to the electronic and chemical sensitization. Density functional theory (DFT) simulation suggests that both the adsorption energy and electron transfer between the VO₂@Pd substrate and NO₂ molecules are optimized synergistically, leading to the improved sensitivity of the gas sensor. Importantly, the strong orbital hybridization between the NO₂ molecule and Pd atom is observed according to density of states (DOS), which is beneficial in selectively improving the NO₂ sensing performance of the VO₂@Pd gas sensor.