The oxidizing effect of humidity on WO3 based sensors

Abstract Semiconducting metal oxide based gas sensors are used in a wide spectrum of fields, ranging from the detection of hazardous gases within the environment to monitoring air quality. WO 3 is the second, after SnO 2 , most commonly used semiconducting metal oxide in commercial gas sensors. Despite its frequent application, the surface reactions responsible for sensing are largely unknown. Here, for the first time, a mechanism for the surface reaction between WO 3 and humidity can be concluded from experimental results. DC resistance measurements and operando diffuse reflectance infrared Fourier transform spectroscopy show an oxidation of the WO 3 lattice during humidity exposure. The filling of oxygen vacancies by water explains the effects atmospheric humidity has on WO 3 based sensors, specifically the increase in resistance, the higher sensor signals to CO and the lower sensor signals to NO 2 . These findings are a basis for understanding how sensing occurs with WO 3 based sensors.

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