Effect of Water Vapor on Pd-Loaded SnO₂ Nanoparticles Gas Sensor

Abstract

The effect of water vapor on Pd-loaded SnO2 sensor was investigated through the oxygen adsorption behavior and sensing properties toward hydrogen and CO under different humidity conditions. On the basis of the theoretical model reported previously, it was found that the mainly adsorbed oxygen species on the SnO2 surface in humid atmosphere was changed by loading Pd, more specifically, for neat SnO2 was O(-), while for 0.7% Pd-SnO2 was O(2-). The water vapor poisoning effect on electric resistance and sensor response was reduced by loading Pd. Moreover the sensor response in wet atmosphere was greatly enhanced by loading Pd. It seems that the electron depletion layer by p-n junction of PdO-SnO2 may impede OH(-) adsorption.

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

“…According to our previous report, oxygen dissociatively adsorbed as O 2− on the SnO 2 surface at 350 °C in dry atmosphere. The adsorption of O 2− is supported by the fact that the electrical resistance is proportional to the P O2 1/4 [9,27]. However, there is a possibility that the adsorption of O − and O 2− occur competitively.…”

Antimony-Doped Tin Dioxide Gas Sensors Exhibiting High Stability in the Sensitivity to Humidity Changes

“…19,30 Sb-SnO 2 powder was dispersed in deionized water using ultrasonic irradiation, after which a Pd(NO 3 ) 2 solution was added to the dispersion. After drying the solution at 120°C, the resulting powder was calcined at 500°C for 3 h to produce the Pd/Sb-SnO 2 nanoparticles.…”

“…This result is in good agreement with previous reports. 19,26 However, in the case of the Sb-SnO 2 sensors, sensor response independent of humidity appears above 16 RH%. In a previous report, we proposed that oxygen adsorption sites around the hydroxyl absorbers are protected from hydroxyl poisoning.…”

“…Based on experimental confirmation, both O − and O 2− form competitively on the SnO 2 surface, and the ratio of these species is influenced by temperature 18 and the composition of the ambient atmosphere. 19,20 In a dry atmosphere, O 2− is the main adsorption species over 350°C, while O 2− and O − are competitively adsorbed at 300°C. 18 Water vapor causes the most harm to SnO 2 -based resistivetype gas sensors, because it adsorbs on the oxygen adsorption site and so interrupts oxygen adsorption.…”

“…According to our previous results, the main oxygen adsorption species transitions from O 2− to O − under humid conditions. 19 Therefore, we theoretically proposed that hydroxyl groups preferentially adsorb on the O 2− adsorption site. 17 Hence, decreasing the quantity of adsorbed oxygen and changing the adsorbed species both significantly reduce the electric resistance and sensor response.…”