Mechanistic Insights into NO 2 Sensing at Room Temperature: Oxygen Vacancy Dynamics Revealed by in Situ 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 in situ optoelectronic spectroscopy, we directly probe oxygen vacancy evolution during NO₂ adsorption. In situ 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.