The understanding of the gas sensing mechanism at a fundamental level implies the knowledge of the state of preadsorbed
surface species. Some question marks on the commonly accepted ideas were raised by the recorded higher
sensitivity of sensors to CO in nitrogen and by the fact that the combustion of CO was observed in air and in humid
nitrogen. These facts question the monopoly of oxygen ions as the reaction partners for CO and they were the driving
force for thereby presented investigations. DRIFT Spectroscopy and resistance measurements have been simultaneously
applied to discriminate between the species that are actively taking part in the sensing processes and spectators. The
comparison between the different sensors has been focused on verifying whether the observed phenomena are general or
whether they depend on the technology. It was observed that for SnO2 sensors, the reaction of oxygen, with water results
in the formation of terminal hydroxyls and the release of an electron to the conduction band. It indicates that water
compete with reducing gases for the oxygen ions. This phenomenon was independent of the technology and thus it
could be SnO2 characteristic. It was shown that CO reacts preferentially with ionosorbed oxygen at the surface of tin
dioxide. In the case of lack of oxygen different scenarios are possibly dependent on hydration state of the surface.
The contribution presents the results obtained in the last years by applying an established aerosol based production
technology for metal oxide nanoparticles mainly used in catalysis and filler materials, the so called flame spray pyrolysis
(FSP), to gas sensor fabrication. The final achievement of this technology is a fast and clean single step process to
fabricate fully functionalized multilayer sensors. This is a substantial progress as it merges the two fundamental
processes of producing the sensing material and fabricating the sensing element.
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