Abstract
The mechanism of CO oxidation on the WO3(001) surface for gas sensing performance has been systematically investigated by means of first principles density functional theory (DFT) calculations. Our results show that the oxidation of CO molecule on the perfect WO3(001) surface induces the formation of surface oxygen vacancies, which results in an increase of the surface conductance. This defective WO3(001) surface can be re-oxidized by the O2 molecules in the atmosphere. During this step, the active O2− species is generated, accompanied with the obvious charge transfer from the surface to O2 molecule, and correspondingly, the surface conductivity is reduced. The O2− species tends to take part in the subsequent reaction with the CO molecule, and after releasing CO2 molecule, the perfect WO3(001) surface is finally reproduced. The activation energy barriers and the reaction energies associated with above surface reactions are determined, and from the kinetics viewpoint, the oxidation of CO molecule on the perfect WO3(001) surface is the rate-limiting step with an activation barrier of about 0.91 eV.
Highlights
Metal oxides are widely used as gas sensitive materials due to their reproducibility and typical surface properties which are suitable for gas detection
The structure of the WO3 (001) surface changes slightly compared to the pristine surface, and the variations of the
The oxidation reactions of Carbon monoxide (CO) molecule on the WO3 (001) surfaces for CO sensing have been systematically investigated by density functional theory (DFT) calculations
Summary
Metal oxides are widely used as gas sensitive materials due to their reproducibility and typical surface properties which are suitable for gas detection. Hübner [18] and co-workers examined the sensing of CO with WO3 -based gas sensors as a function of the oxygen background conditions, which attracted our great interest and attention They recorded CO2 formation when CO was exposed to the WO3 surface in spite of a very low oxygen partial pressure. A series of first principle calculations have been performed by Tian’s group [23,24] Their results further confirm the significance of CO oxidation process for WO3 sensing mechanism, and suggest that the existence of the oxygen vacancies decreased the sensitivity of WO3 surface towards CO to some extent. We reveal the role of oxygen vacancies and active oxygen species on the sensing performance of WO3 -based materials
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