Sensing Properties and Mechanism of Gas Sensors Based on Room-Temperature Solution Processed NiO-Niv Nanoparticles

Developing high-performance, energy-efficient, and cost-saving metal oxide-based gas sensors for NO2 detection at room temperature is of immense importance. In this work, nonstoichiometric NiO-Niv was prepared by a low-cost chemical coprecipitation method and then deposited as a sensing film for NO2 detection at RT without further postannealing. The NiO-Niv sensor showed a maximal response value of 12.42 toward 20 ppm of NO2 gas, 7.8 times higher than that of the pure NiO. Moreover, it exhibited quite high selectivity and stability to NO2 gas, with its properties almost maintained even after 1 month. This exceptional sensing performance might be attributed to the unique surface morphology and abundant nickel vacancies that induced high activity in NiO-Niv. To investigate the sensing mechanism, the adsorption energy and charge density difference were calculated by first-principles calculations based on the density functional theory. It demonstrated that NiO with nickel vacancy can adsorb NO2 more easily and that there was more charge transfer between NiO-Niv and NO2 molecules compared to that of pure NiO. Furthermore, a potential gas-sensing mechanism involving nickel vacancies was proposed to elucidate the origin of the enhanced sensing property. The improved strategy can be broadly applied to p-type semiconductor-based gas sensors.