Mechanistic Insights into NO ₂ Sensing at Room Temperature: Oxygen Vacancy Dynamics Revealed by <i>in Situ</i> Optoelectronic Characterization

Understanding light-defect-gas interactions at the molecular level is central to designing energy-efficient chemical sensors. While photogenerated carriers are recognized mediators, the dynamic role of photoactivated oxygen vacancies remains unexplored. Through <i>in situ</i> optoelectronic spectroscopy, we directly probe oxygen vacancy evolution during NO₂ adsorption. <i>In situ</i> DRIFTS and Raman analyses establish that oxygen vacancy states govern surface oxygen speciation, revealing that photoactivated vacancies─not electron-hole pairs─dominate room-temperature sensing kinetics. This work provides direct mechanistic evidence of defect-mediated adsorption, a generalizable framework for light-defect interactions in semiconductors, and foundational principles for engineering oxygen-vacancy dynamics in surface processes, such as photocatalysis and optoelectronics.