Insight into the Mechanism of CO Oxidation on WO₃(001) Surfaces for Gas Sensing: A DFT Study.

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.