(Keynote) Progress in the Development of Metal Oxide Gas Sensors to Reduce Carbon Footprint
The real-time detection of gas composition is essential for improving efficiency in industrial process and to lower the greenhouse gas (GHG) emissions. CO2, one of the major components of GHGs, encounters a challenge on being monitored at real-time under harsh environmental conditions. Spectroscopic and optical techniques based on infrared radiation are commonly used to detect CO2 at room temperature, however, the in situ monitoring of the gas species by placing such sensors directly at high temperature and aggressive environment is practically incompatible due to their size and stability issues. Na+ and Li+ ion conducting electrolytes (e.g., Na-β-alumina, NASICON-type), and Na2CO3 and BaCO3 electrodes have been widely employed to fabricate all-solid-state EMF CO2 sensor. On the other hand, SnO2, TiO2 and WO3 as semiconductor-based sensors were also used as resistive-type CO2 sensors. In both cases, the stability and cross sensitivities, however, have remained as major obstacles. Our approach was, therefore, to use perovskite oxides (POs) in semiconductor-based gas sensors, for their high thermal and chemical stability, which in turn improve sensor's reliability and long-term performance. In addition, the doping flexibility in POs allowed us to prepare transition metal-doped perovskites. The critical role of dopant on CO2 sensing properties is discussed. The future prospect of using nanotech with its ability to precisely control the structure of these materials may guide CO2 sensors into a whole new level.