WO₃-Based Gas Sensors: Identifying Inherent Qualities and Understanding the Sensing Mechanism

Semiconducting metal oxide-based gas sensors are an attractive option for a wide array of applications. In particular, sensors based on WO₃ are promising for applications varying from indoor air quality to breath analysis. There is a great breadth of literature which examines how the sensing characteristics of WO₃ can be tuned via changes in, for example, morphology or surface additives. Because of variations in measurement conditions, however, it is difficult to identify inherent qualities of WO₃ from these reports. Here, the sensing behavior of five different WO₃ samples is examined. The samples show good complementarity to SnO₂ (the most commonly used material)-based sensors. A surprising homogeneity, despite variation in morphology and preparation method, is found. Using operando diffuse reflectance infrared Fourier transform spectroscopy, it is found that the oxygen vacancies are the dominant reaction partner of WO₃ with the analyte gas. This surface chemistry is offered as an explanation for the homogeneity of WO₃-based sensors.