Interplay between O₂ and SnO₂: Oxygen Ionosorption and Spectroscopic Evidence for Adsorbed Oxygen

Abstract

Tin dioxide is the most commonly used material in commercial gas sensors based on semiconducting metal oxides. Despite intensive efforts, the mechanism responsible for gas-sensing effects on SnO(2) is not fully understood. The key step is the understanding of the electronic response of SnO(2) in the presence of background oxygen. For a long time, oxygen interaction with SnO(2) has been treated within the framework of the "ionosorption theory". The adsorbed oxygen species have been regarded as free oxygen ions electrostatically stabilized on the surface (with no local chemical bond formation). A contradiction, however, arises when connecting this scenario to spectroscopic findings. Despite trying for a long time, there has not been any convincing spectroscopic evidence for "ionosorbed" oxygen species. Neither superoxide ions O(2)(-), nor charged atomic oxygen O,(-) nor peroxide ions O(2)(2-) have been observed on SnO(2) under the real working conditions of sensors. Moreover, several findings show that the superoxide ion does not undergo transformations into charged atomic oxygen at the surface, and represents a dead-end form of low-temperature oxygen adsorption on reduced metal oxide.

Novel method for the detection of short trace gas pulses with metal oxide semiconductor gas sensors

“…The types of oxygen species at the sensor surface are discussed controversially in the literature. There is no spectroscopic evidence for the oxygen interaction with metal oxides (Gurlo, 2006 (Pulkkinen et al, 2001). Other authors expect the double charged atomic ion O 2− to be the predominant species in dry air between 350 and 450 • C, and a competitive adsorption of O − and O 2− around 300 • C (Suematsu et al, 2014).…”

CO oxidation over Pt/SnO2 catalysts

“…600°C and for the second at over 800°C. TPD-O 2 studies over SnO 2 have been reported in a few works [17,21,[39][40][41]. The general conclusion is that the course of TPD-O 2 strongly depends on the pretreatment of the catalyst surface preceding the process of desorption.…”

Multi-functional properties of CaCu3Ti4O12 thin films

“…21,22 In addition, the conductance in n-type semiconductor oxides is dependent on oxygen partial pressure, and it decreases when the oxygen partial pressure increase (the inverse is valid for p-type semiconductor oxides). 23,24 Based on these fundamentals, sensor measurements were performed to determine the dominant charge carriers for CCTO films prepared by the PPM and to verify the gas sensitivity of the material (sensor characteristics). The gas test was performed with an oxygen concentration at 12% and varying operating temperatures (200 C, 250 C, and 300 C) (see Figure 2).…”