Ambient Humidity Influence on CO Detection with SnO2 Gas Sensing Materials. A Combined DRIFTS/DFT Investigation

Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and first-principles calculations are performed to investigate the different ways in which water reacts with a SnO2 surface and to evaluate the cross interference of humidity on the detection of CO. Two different materials, chosen because of their very different properties, are investigated. The experimental results are interpreted with the help of theoretical modeling of two clean and defective surfaces, namely, (110) and (101). The experimental results show, and the theoretical calculations confirm, that water vapor can interfere with the CO detection in different ways depending on the active surface and the concentration of oxygen vacancies. This is related to the different ways in which the water vapor reacts with tin oxide: on the one hand, it can reduce the (101) surface; on the other hand, it can heal the oxygen vacancies of the defective (110) surface.