Understanding the Sensing Mechanism of WO3 based Gas Sensors

The first commercially available semiconducting metal oxide gas sensor, patented by Taguchi in the 1970s, was based on SnO
₂
. Even today, most commercially produced sensors are based on SnO
₂
. As computing power becomes more prevalent and metal oxide gas sensors are used in a broader range of applications, materials with complementary sensing characteristics will be needed. WO
₃
is a promising material that shows high responses to volatile organic compounds and NO
₂
. Interestingly, humidity is reported to have an oxidizing effect on the material, which is the opposite of what is commonly reported for SnO
₂
. Here the surface reaction which is responsible for the sensing mechanism of NO
₂
is examined using diffuse reflectance infrared Fourier transform spectroscopy. The effect of humidity on the sensor response is understood and a comparison to SnO
₂
is made.