Catalytic property tuned ozone gas sensing performance of cobalt oxides

Understanding the relationship between catalytic properties and gas sensing performance in metal oxide semiconductors is essential for elucidating reaction mechanisms and designing highly-sensitive, active materials. In this study, cubic CoO with octahedral [CoO₆] coordination, wurtzite CoO with tetrahedral [CoO₄] coordination and spinel Co₃O₄ with mixed [CoO₆] and [CoO₄] coordination were synthesized. Though cubic CoO showed higher catalytic activity at 20-100 ℃ and wurtzite CoO had higher activity at 60-100 ℃, the ozone sensing response of Co₃O₄ was higher at the optimized working temperature of 60 ℃. In situ infrared reflectance spectroscopy revealed the presence of abundant intermediates in the catalytic process of Co₃O₄, benefiting the electron transfer and the resultant resistance change of the sensor. Furthermore, Co₃O₄ calcined at 600 ℃ with 3 at.% Sn doping showed the highest sensitivity (response = 55 to 1 ppm ozone) at 60 ℃ and excellent selectivity toward interfering gases, including formaldehyde, ethanol, acetone, and xylene. These findings infer that catalytic intermediates rather than decomposition efficiency play a more important role in gas sensing.