Interaction of water, hydrogen and their mixtures with SnO2 based materials: the role of surface hydroxyl groups in detection mechanisms

Abstract

DRIFTS, TGA and resistance measurements have been used to study the mechanism of water and hydrogen interaction accompanied by a resistance change (sensor signal) of blank and Pd doped SnO(2). It was found that a highly hydroxylated surface of blank SnO(2) reacts with gases through bridging hydroxyl groups, whereas the Pd doped materials interact with hydrogen and water through bridging oxygen. In the case of blank SnO(2) the sensor signal maximum towards H(2) in dry air (R(0)/R(g)) is observed at approximately 345 degrees C, and towards water, at approximately 180 degrees C, which results in high selectivity to hydrogen in the presence of water vapors (minor humidity effect). In contrast, on doping with Pd the response to hydrogen in dry air and to water occurred in the same temperature region (ca. 140 degrees C) leading to low selectivity with a high effect of humidity. An increase in water concentration in the gas phase changes the hydrogen interaction mechanism of Pd doped materials, while that of blank SnO(2) is unchanged. The interaction of hydrogen with the catalyst doped SnO(2) occurs predominantly through hydroxyl groups when the volumetric concentration of water in the gas phase is higher than that of H(2) by a factor of 1000.

Active Sites on Nanocrystalline Tin Dioxide Surface: Effect of Palladium and Ruthenium Oxides Clusters

“…The lower vibrational wavenumber (3400−3200 cm −1 ) of OH···OH compared to isolated OH species (3640−3500 cm −1 ) mirrors the O−H bond loosening and strengthening of that of M−OH that is typical for rooted hydroxyls. 30 The reason for increased impact of OH···OH to the hydrated species of modified samples might be a larger concentration of rooted OH groups and/or their higher acidic nature, which for SnO 2 /PdO x agrees with TPD-NH 3 data. Noteworthy, with the FTIR patterns of modified samples looking similar, the OH surf and H 2 O surf absorption bands of SnO 2 /PdO x were more intense ( Figure 6).…”

Effect of Humid Aging on the Oxygen Adsorption in SnO2 Gas Sensors

“…As shown in Figure 4b, we observed that humid aging enhanced the oxygen adsorption. Thus, an increase in the amount of oxygen on the surface by the humid aging facilitated the combustion of hydrogen, thereby suppressing the hydroxyl poisoning [16,17,18]. However, in high wet air (P H2O : 0.03 atm), the sensor response became less than S = 10.…”

“…Water vapor, which is always present in the atmosphere, has been recognized as the most harmful gas for semiconductor-type sensors because the adsorbed water blocks the oxygen adsorption on the surface (hydroxyl poisoning) [6,7,16,17,18]. The formation of hydroxyl groups on Sn 4+ sites can be expressed by the following equation [16]:H 2 O + O − ad (or O 2− ad ) + 2Sn → 2(Sn-OH) +e − (or 2e − ) …”

Investigating the influence of Al-doping and background humidity on NO<sub>2</sub> sensing characteristics of magnetron-sputtered SnO<sub>2</sub> sensors

“…(Pavelko et al, 2010). While the effect of background water and oxygen species on gas sensing properties of SnO 2 materials has recently been reported (Korotcenkov et al, 2007;Großmann et al, 2013), this issue is still a subject of debate due to the complexity of this matter.…”