The role of oxygen vacancies on SnO2 surface in reducing cross-sensitivity between ambient humidity and CO: A first principles investigation

Abstract

The sensing properties of SnO2 based CO gas sensors can be affected by ambient humidity and oxygen pressure. In this study the effect of oxygen vacancy along with the adsorption mechanism of H2O and CO on SnO2 (110) surface has been investigated by performing density functional theory (DFT) calculations. The influence of ambient humidity has been taken into consideration in order to better understand the CO sensing mechanism in SnO2 based gas sensors. Molecular and dissociative adsorption of H2O on both stoichiometric and oxygen deficient surface were simulated. Adsorption energies, Bader charge analysis and the projected density of states were investigated by employing electronic structure calculations. The findings show that CO adsorption in most cases is less favorable in the presence of H2O and on the reduced SnO2 surface. However, oxygen vacancies provide more sites to adsorb H2O molecules to compensate the humidity cross-interference. Furthermore, CO to CO2 conversion along with dissociative H2O adsorption on the vacancy of oxygen site presents the highest charge transfer and very strong adsorption energy among other adsorption configurations. These findings provide a guideline for fabricating more efficient CO sensors.