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

Abstract

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 O2 – 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 O2 – 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 (O2 –, 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.

Ab initio thermodynamic study of the SnO2(110) surface in an O2 and NO environment: a fundamental understanding of the gas sensing mechanism for NO and NO2

“…This result is reasonably consistent with the previous DFT works [43,[62][63][64] and the general insight of surface stability.…”

“…When compared with Al 2 O 3 surface, NO adsorbate had also N-down orientation [65]. In the case of CO adsorption on SnO 2 (110) surface [43], C-down orientations were mainly observed, being similar to NO adsorption. (Fig.…”

“…In this case, the resonances of peaks appear around −6.4 eV, −7.5 eV and −1.4 eV for hybridizations between O br -2P states and NO-3σ, 1π, 2π * orbitals, respectively, as can be seen in Fig. 10 In the sensing mechanism of SnO 2 compared to other gas like CO and ethanol, it was described that CO adsorption on the surface causes the taking off the surface oxygen atoms like O br and thus reduction of the surface [12,43,44]. Unlike this, it is not easy for NO to desorb O br but only possible to take off one oxygen atom of O 2dm because of relatively weak reducibility of NO.…”

“…This is recognized as a preliminary stage of gas sensing [10,30,31,43,44], since it has become clear that pre-adsorbed oxygen species O − 2 and O − on the surface grab electrons from the surface, resulting in an increase of the surface resistance [3,7,10,12]. In this work we suggest eight different models for SnO 2 (110) surface in contact with oxygen gas using (1×1) and (2×1) surface unit cells, as shown in Fig.…”

“…Compared to the CO sensing mechanism of SnO 2 (110) surface [43][44][45][46][47], the sensing properties strongly depends upon the concentration of oxygen in the ambient atmosphere: CO reacts with either directly stoichiometric surface or oxygen species O − 2 or O − , accompanying the release of electrons to the surface with or without formation of CO 2 [43].…”