Hydrogen sulfide, the formula H₂S, is an important chemical raw material, a flammable acidic gas under the standard condition with colorless, smelling like rotten eggs at low concentrations, has highly toxic, and its solution in the water is called the hydrogen sulfate. Hydrogen sulfide is a flammable hazardous chemicals, which can be formed to the explosive mixtures with the air; and when it meets with an open fire and high-heat, it will cause combustion and explosion. Even low concentrations of hydrogen sulfide can damage a person's sense of smell; but there is no odor at high concentrations (because the olfactory nerve will be palsied by the high concentration of hydrogen sulfide), so the way to use the nose to detect this gas is fatal. Therefore, the use of certain testing tools and instruments to detect its concentration is very necessary.

 

Hydrogen sulfide gas sensor is used to monitor the concentration of hydrogen sulfide in the air, gas sensor generally consists of two sheets: one sheet for heating, and the other sheet is the gas sensing film which is sensitive to hydrogen sulfide. WO₃ based gas material is considered to be one of the most promising new oxide sensitive material to detect hydrogen sulfide. The first time to reported WO₃ based gas material for the detection of hydrogen sulfide gas was in 1990, which is reported that WO₃ has high sensitivity on 0.005% of hydrogen sulfide at the temperature of 469K; even though the response time is quite long (up to 90% of steady resistance response time 7~8 minutes), this achievement still made a great contribution to promote the development of WO₃-based hydrogen sulfide gas-sensitive materials. And thereafter, the preparation of WO₃ based thin or thick film of hydrogen sulfide gas sensitive material has gradually become active again, and also the study on structure, electrical properties, sensing mechanism.

 

The mechanism of WO₃ based gas sensors of hydrogen sulfide gas is that when the tungsten trioxide contact with hydrogen sulfide, it will cause number of negative electron carriers increased, thereby causing the resistance of the n-type semiconductor WO₃ decline. In addition, there are reports about precious metals (Au, Pd, Pt, etc.) doping to affect the property of WO₃ based gas sensor, which makes the response time to reach 90% of the steady resistance shortened to less than 1s. Thus we will see the noble metal doping can greatly enhance the sensitivity of the semiconductor gas sensor.