Proof of Concept for Operando Infrared Spectroscopy Investigationof Light-Excited Metal Oxide-Based Gas Sensors

Light-excitation of semiconducting metal-oxide (SMOX)-based gas sensors is apromising means to lower their operation temperature, thereby reducing power consumption,which would allow for their broader application. Despite increased research interest in light-excited gas sensors, progress has been slow because of a lack of mechanistic understanding.Notably, significant differences between light-excitation and, the better understood, thermal-excitation mechanisms have been identified. Insights from operando spectroscopic studies havebeen key to understanding the surface chemistry that determines the performance of thermallyactivated SMOX, but they have not yet been performed on illuminated sensors. Here, for thefirst time, we demonstrate that it is possible to perform operando diffuse reflectance infraredFourier transform (DRIFT) spectroscopy measurements on sensors under illumination. Wedemonstrate the benefits of the approach and show that under light illumination the splittingof water on the WO3surface is responsible for the increased resistance of the sensor duringexposure to high humidity.