Ceria-doped SnO2 sensor highly selective to ethanol in humid air

In our earlier study, we reported that at 300 °C, a 2.0 wt.% CeO2-doped SnO2 sensor is highly selective to ethanol in the presence of CO and CH4 gases [F. Pourfayaz, A. Khodadadi, Y. Mortazavi, S.S. Mohajerzadeh, CeO2 doped SnO2 sensor selective to ethanol in presence of CO, LPG and CH4, Sens. Actuators B 108 (2005) 172–176]. In the present investigation, we report the influence of ambient air humidity on the ethanol selective SnO2 sensor doped with 2.0 wt.% CeO2. Maximum response to ethanol occurs at 300 °C which decreases with the relative humidity. The relative humidity was changed from 0 to 80% for different ambient air temperatures of 30, 40 and 50 °C and the response of the sensor was monitored in a 250–450 °C temperature range. As the relative humidity in 50 °C air increased from 0 to 30%, a 15% reduction in the maximum response to ethanol was observed. A further increase in the relative humidity no longer reduced the response significantly. The presence of humidity improved the sensor response to both CO and CH4 up to 350 °C after which the extent of improvement became smaller and at 450 °C was almost diminished. The sensor is shown to be quite selective to ethanol in the presence of humid air containing CO and CH4. The selectivity passes a maximum at 300 °C; however it declines at higher operating temperatures.