Optimizing the Stability of Co 3 O 4 for Acetone Sensing by Oxygen Vacancy Alteration

An increase in surface-adsorbed oxygen species presents unique opportunities to improve the sensing performance of metal oxide-based gas sensors. However, the instability of surface-adsorbed oxygen species, especially in the gas sensing process, decreases the sensing performance. This study reveals the performance‒stability paradox of surface-adsorbed oxygen species for Co3O4-based acetone sensors. A hydrothermal synthesis method assisted by P123 was used to prepare Co3O4 with an appropriate surface-adsorbed oxygen species (designated as Co3O4-AP). Unlike Co3O4 with less surface-adsorbed oxygen species, as-prepared Co3O4-AP exhibited a high response value of 19.0 (100 ppm acetone) on the first day but decreased to 13.9 on the seventh day, with a relative standard deviation of 15.7% in terms of resistance and 15.0% in terms of response values, respectively, owing to the loss of surface-adsorbed oxygen species during the sensing process (mainly the filling of oxygen vacancies by O2). Owing to the instability of surface-adsorbed oxygen species, aging at 240 °C in air for 2 days was rationally performed for Co3O4-AP, decreasing the surface-adsorbed oxygen species concentration and improving the stability of Co3O4-AP. Notably, after aging for 2 days, the Co3O4-AP sensor achieves a response value of 12.9 (100 ppm acetone), high selectivity, and good stability (relative standard deviations of 7.0 and 9.1% in terms of resistance and response values, respectively), outperforming acetone sensors based on Co3O4 obtained by hydrothermal synthesis without P123 (7.2), the coprecipitation method (7.6), and the direct calcination method (3.5). Our work provides new insights into overcoming the performance‒stability trade-off and designing highly stable and high-performing gas sensors.