Density Functional Study of Nitric Oxide Adsorption on the Monoclinic WO3 (001) Surface

Abstract

Tungsten oxide (WO3) is an important n-type semiconductor widely used in resistive gas sensing applications. Understanding the microscopic mechanism governing gas adsorption and the resulting modification of electronic properties is essential for improving sensor performance. In this work, density functional theory calculations based on the full potential linearized augmented plane wave (FP-LAPW) method are implemented to investigate nitric oxide adsorption on the monoclinic WO3 (001) surface. Structural optimization and electronic structure calculations are carried out using the generalized gradient approximation in the Perdew-Burke-Ernzerhof form, the modified Becke-Johnson potential and the Hubbard +U correction. A (2×2×1)-slab model with a vacuum thickness of 15 ˚A is constructed to simulate the surface. The results show that nitric oxide (NO) adsorption modifies the electronic structure of WO3 and reduces the band gap due to enhanced hybridization between the W-5d and the O-2p states. Among the considered adsorption configurations, adsorption at the tungsten top site in a bent geometry is found to be energetically most favorable with an adsorption energy of approximately −1.42 eV. The electronic redistribution induced by adsorption leads to increased conductivity, providing a microscopic explanation for NO sensing in WO3 based gas sensors.