Sensing Mechanism of SnO2 (110) Surface to CO: Density Functional Theory Calculations

We investigated the CO sensing mechanism of SnO2 (110) surface by density functional theory calculation. The CO sensing mechanism of SnO2 surface strongly depends upon the concentration of oxygen in the ambient atmosphere. For very high oxygen concentration where oxygen species O-2(-) or O- are not adsorbed on the stoichiometric SnO2 (110) surface, there is the direct interaction between CO and the stoichiometric surface through the CO adsorption on Sn site or formation of CO2, accompanying the release of electrons to the surface. For the considerable high oxygen concentration, the oxygen species O-2(-) and O- adsorbed on the oxygen-deficient SnO2 (110) surface grab electrons mainly from Sn atoms of SnO2 (110) surface. When SnO2 (110) surface is exposed to CO reducing gas, the interactions between CO and preadsorbed oxygen species (O-2(-), O-) as well as some lattice atoms at certain sites on SnO2 surface lead to the releasing of electrons back to semiconductor SnO2. At very low oxygen concentration, the structural reconstruction is induced by the direct interaction between CO and SnO2 subreduced surface with the removing of 2-fold-coordinated bridging oxygen rows, accompanying the electron transfer from CO to the surface without the formation of CO2 in the sensing response process.