NANOCRYSTALLINE WO3-BASED H2S SENSORS

Nanocrystalline (NC) materials, exhibiting a large surface area, may be applied to gas sensors for which an excellent surface effect is required. In this study, tungsten oxide is synthesized by the gas-evaporation method and a mean particle size of about 10 nm is obtained. A step-heating sintering process is used to obtain the porous network-like structure of NC WO3. The results indicate that nanocrystalline WO3 is better than thin-film WO3 in sensing the H2S gas. The amount of dopants influences the sensitivity and the optimum operating temperature. An increasing weight percentage of Pd dopant will at first increase the sensitivity and lower the optimum operating temperature in 100 ppm H2S/air. But if excess dopant is added, e.g., if NC WO3 is 13.5 wt.% Pd-doped, it will oxidize at a high temperature and its characteristics of activating the detected gases on the surface of NC WO3 will disappear. The sensor thus loses the ability to sense at low temperature. Sensitivities of 9.9 and 9.7 can be achieved in 7.7 wt.% Pt-doped NC WO3 at 220 degrees C and 7.2 wt.% Pd-doped NC WO3 at 170 degrees C under 100 ppm H2S/air, respectively. The response times of 7.2 wt.% Pd-doped NC WO3 at 170 degrees C and 7.7 wt.% Pt-doped NC WO3 at 220 degrees C are less than 0.11 s.