Ammonia Sensor Using Noble Metal-Loaded Tungsten Trioxide.

Abstract

In an effort to develop a semiconductor type NH3 sensor, the NH3 sensing properties of WO3 semiconductors loaded with colloidal noble metals were investigated. Among the various noble metals tested, Au was proven to be the most excellent promoter for the WO3-based NH3 sensor, whereas Pt gave a very high NH3 sensitivity at 200°C, but the response was too slow. Thus Au-WO3 element could respond to NH3 in air over a wide NH3 concentration range of 5 ppb-50 ppm at 450°C, showing excellent characteristics in both NH3 sensitivity and response rate. An optimum Au loading amount was shown to be 0.8 wt % with respect to the NH3 sensitivity. The electrical resistance of Au-WO3 element in air increased with an increase in Au loading. From the measure-ments of Seebeck coefficients it was revealed that the Au particles loaded interact with WO3 and take the conduction electrons away when exposed to air, while those electrons are given back to WO3 on exposure to NH3-containing atmospheres. It is concluded that such an electronic interac-tion between Au and WO3, susceptible to a change in atmosphere, is responsible for the prominent promoter action of Au.