DFT study on interaction of NO2 with the vacancy-defected WO3 nanowires for gas-sensing

The gas response of oxide-based sensors strongly depends on its surface properties. To explore the potential sensing ability of one-dimensional (1D) WO3 nanowire under existence of oxygen vacancy, the adsorption of NO2 molecule on the oxygen vacancy defected surface of WO3 nanowire was studied using density functional theory (DFT) calculations. Three kinds of stable oxygen vacancies were considered, and the three corresponding most energetically favorable adsorption configurations were constructed based on the calculation adsorption energy. The electronic properties including density of states, band structure and atomic Mulliken population were further studied. It is found that the existence of oxygen vacancies benefits NO2 adsorption on nanowire surface, and makes the interaction between molecule and vacancy-defected surface strengthened markedly. Consequently, the electronic structures and electronic properties of the defective WO3 nanowires were tuned obviously, causing a distinct change of the density of state at Fermi level and much more electrons extracted from the defective surface. The transferred electrons from the vacancy-defected WO3 nanowire was four to six times more, depending on different oxygen vacancies, than that from the stoichiometric nanowire, indicating a positive effect of oxygen vacancy on NO2-sensing response. The results highlight the possibility to develop high sensitive NO2 gas sensors through introducing oxygen vacancy defects in WO3 nanowire.