Density functional theory study of the NO₂-sensing mechanism on a WO₃ (0 0 1) surface: the role of surface oxygen vacancies in the formation of NO and NO₃

ABSTRACT

The trapping and detection of nitrogen oxide with tungsten trioxide has become a popular research topic in recent years. Knowledge of the complete reaction mechanism for nitrogen oxide adsorption is necessary to improve detector performance. In this work, we used density functional theory (DFT) calculations to study the adsorption characteristics and electron transfer of nitrogen dioxide on an oxygen-deficient monoclinic WO₃ (0 0 1) surface. We observed different reactions of NO₂ on slabs with different O- and WO-terminated WO₃ (0 0 1) surfaces with oxygen vacancies. Our calculations show that the bridging oxygen atom on an oxygen defect on an O-terminated WO₃ (0 0 1) surface is the active site where an NO₂ molecule is oxidised into nitrate and is adsorbed onto the surface. On a WO-terminated (0 0 1) surface, one of the oxygen atoms from the NO₂ molecule fills the oxygen vacancy, and the resulting NO fragment is adsorbed onto a W atom. Both of these adsorption models can cause an increase in the electrical resistance of WO₃. We also calculated the adsorption energies of NO₂ on slabs with different oxygen-deficient WO₃ surfaces.

KEYWORDS:

• Density functional theory
• oxygen vacancy
• nitrate
• mechanism

Acknowledgment

We are very grateful to Feng Xin for his effort on revising this manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China (NSFC) [grant number 21176192]; the Tianjin Natural Science Foundation [grant number 12JCZDJC29400].