Semiconducting Metal Oxide Gas Sensors—Exploring the Nature of Siloxane Poisoning Mechanisms

Semiconducting metal oxide (SMOX) based gas sensors are cheap, easy to manufacture, battery powered, respond rapidly and when used in an array can detect specific gases. These qualities make them attractive for different applications ranging from indoor air quality monitoring to industrial safety. SMOX sensors are more robust than other options, e.g. electrochemical sensors, and can therefore be used in applications that require elevated temperature and with large variation in humidity. Nonetheless commercially available SMOX sensors, largely based on SnO2, are known to significantly degrade in the presence of siloxane vapors (Si-O-Si bond). Over the past 10 years, the number of products containing siloxanes, e.g. hair and body products, oil-based lubricants, sealants and even anti-foaming agensts, have continuously increased. As a result of this omnipresence, simply avoiding siloxanes is no longer feasible. The intentional design of more robust sensors requires an understanding of why even low siloxane concentrations degrade SnO2 based sensors. Through systematic comparison with two other n-type materials, In2O3 and WO3, already used for sensors, it will be explored how the acidity of the oxide influences its susceptibility to degradation by siloxanes. Insights into the mechanism will be gained from simultaneous in-operando DRIFT spectroscopy and EIS. Understanding the relation between material acidity and its propensity for degradation is essential for identifying intrinsically robust oxides.