Surface kinetics studies on gas sensors: an operando DRIFT approach

The increasing demand for precise detection of gaseous molecules towards diverse applications has led to expanding research for high-performance semiconductor-based chemical sensors. In particular, the employment of nanostructured materials in sensing films has stimulated the development of chemiresistive gas sensors, demonstrating that a change of nanostructures morphology leads to a change of active surface area and ultimately to the gas sensor sensitivity. Therefore, it becomes fundamental to deeply investigate the chemical phenomena occurring at the sensing film surfaces while analyzing the connected variations of the electronic structure and sensing characteristics. This correlation has become critical in chemical sensors since it represents the core of the gas-detection mechanism. Among the arsenal of characterization tools available to support mechanistic proposals, Fourier-transform infrared spectroscopy (FTIR) spectroscopy has been known for the investigation of surface chemistry of nanostructured materials. This work deals with the experimentation of a new ambient chamber for the use in diffuse reflectance Fourier infrared spectroscopy studies on chemoresistive gas sensors in operando condition [1]. This system can support the study of gas-solid phase reactions at the sensor’s surface during their operation, providing a reliable characterization tool that can be easily re-produced, implemented and adapted for several types of gas sensing devices. A deepened investigation was carried out: design of the chamber and the coupled acquisition system with temperature and humidity monitoring, 3D modelling, fluid dynamics study via residence time distribution analysis and temperature gradient evaluation. Then, the system was validated in the case of a SnO2 sensor exposed to hydrogen gas flow. The new developed low void-volume gas sensing system is easy to machine, to use, to maintain and it can be employed with solid-state gas sensors with an active area of 1 mm2 and operating temperatures up to 650°C. To improve and facilitate the spectra acquisition, the system is equipped with precision staging and alignment, and it is fully compatible with Harrick Scientific’s diffuse reflectance. Investigations on electrical properties and sensing mechanisms of semiconductors-based gas sensor in themo-activation mode will be discussed [2,4] and a novel setup for photoactivation mode in operando condition will be presented.