Optimizing the Stability of Co₃O₄ 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.