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

Koichi Suematsu; Nan Ma; Ken Watanabe; Masayoshi Yuasa; Tetsuya Kida; Kengo Shimanoe

doi:10.3390/s18010254

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

Sensors (Basel). 2018 Jan 16;18(1):254. doi: 10.3390/s18010254.

Authors

Koichi Suematsu¹, Nan Ma², Ken Watanabe³, Masayoshi Yuasa⁴, Tetsuya Kida⁵, Kengo Shimanoe⁶

Affiliations

¹ Department of Advanced Materials Science and Engineering, Faculty of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan. shimanoe.kengo.695@m.kyushu-u.ac.jp.
² Department of Molecular and Material Science, Interdisciplinary Graduate School of Engineering Science, Kyushu University, Kasuga, Fukuoka 816-8580, Japan. manan.0611@gmail.com.
³ Department of Advanced Materials Science and Engineering, Faculty of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan. watanabe.ken.331@m.kyushu-u.ac.jp.
⁴ Department of Advanced Materials Science and Engineering, Faculty of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan. yuasa@fuk.kindai.ac.jp.
⁵ Department of Advanced Materials Science and Engineering, Faculty of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan. tetsuya@kumamoto-u.ac.jp.
⁶ Department of Advanced Materials Science and Engineering, Faculty of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan.

Abstract

To investigate the effect of aging at 580 °C in wet air (humid aging) on the oxygen adsorption on the surface of SnO₂ particles, the electric properties and the sensor response to hydrogen in dry and humid atmospheres for SnO₂ resistive-type gas sensors were evaluated. The electric resistance in dry and wet atmospheres at 350 °C was strongly increased by humid aging. From the results of oxygen partial pressure dependence of the electric resistance, the oxygen adsorption equilibrium constants (K₁; for O^- adsorption, K₂; for O^2- adsorption) were estimated on the basis of the theoretical model of oxygen adsorption. The K₁ and K₂ in dry and wet atmospheres at 350 °C were increased by humid aging at 580 °C, indicating an increase in the adsorption amount of both O^- and O^2-. These results suggest that hydroxyl poisoning on the oxygen adsorption is suppressed by humid aging. The sensor response to hydrogen in dry and wet atmosphere at 350 °C was clearly improved by humid aging. Such an improvement of the sensor response seems to be caused by increasing the oxygen adsorption amount. Thus, the humid aging offers an effective way to improve the sensor response of SnO₂ resistive-type gas sensors in dry and wet atmospheres.

Keywords: SnO2; gas sensors; humid aging; hydrogen sensing; hydroxyl poisoning; oxygen adsorption.