Surface-modification of SnO2 nanoparticles by incorporation of Al for the detection of combustible gases in a humid atmosphere

Inhibition of hydroxyl poisoning of SnO2 nanoparticles is important to develop a highly sensitive combustible gas sensor that functions in a humid atmosphere. For this purpose, we incorporated Al into SnO2 nanoparticles (Al-doped SnO2) by a precipitation method, and fabricated a thick-film-type sensor using a screen printing method. Bare SnO2 nanoparticles and Al2O3-loaded SnO2 nanoparticles were also prepared for comparison. The oxygen adsorption amount clearly decreased after Al doping and Al2O3 loading, according to temperature programmed desorption measurements. Al doping enhanced the sensor response (sensitivity) to H2, CO and C2H5OH in a humid atmosphere by almost five to ten times. Al2O3 loading also slightly increased the sensor response to each gas in a humid atmosphere. The enhancement of the sensor response was attributed to both Al and Al2O3 acting as hydroxyl absorbers on the surface of the nanoparticles, thereby providing an oxygen adsorption site for surface combustion reactions in a humid atmosphere. Based on the relationship between the sensor response and C2H5OH concentration, it was estimated that Al-doped SnO2 can detect less than one ppm C2H5OH in a humid atmosphere. Therefore, doping with Al, which protects and holds the adsorbed oxygen on the surface of the SnO2, is important as a surface modification to obtain humidity-tolerant semiconductor gas sensors.