CO₂‐Driven Oxygen Vacancy Diffusion and Healing on TiO₂(110) at Ambient Pressure

Understanding how TiO 2 interacts with CO 2 at the molecular level is crucial in the CO 2 reduction toward value‐added energy sources. Here, we report in situ observations of the CO 2 activation process on the reduced TiO 2 (110) surface at room temperature using ambient pressure scanning tunneling microscopy. We find that oxygen vacancies (V o ) diffuse dynamically along the bridging oxygen (O br ) rows of the TiO 2 (110) surface under ambient CO 2 (g) environments. This physical phenomenon exclusively occurs when the oxygen abstracted upon CO 2 dissociation instantly occupies the V o sites of O br rows on the TiO 2 (110), whereas the TiO 2 (110) surface without the V o only allows CO 2 physisorption on five‐fold‐coordinated Ti 4+ sites. Synchrotron‐based ambient pressure X‐ray photoelectron spectroscopy also identifies the changes in surface oxidation states of TiO 2 (110) by the healing of V o sites or the CO 2 physisorption under ambient CO 2 (g) conditions. Density functional theory calculations propose a mechanism of the CO 2 ‐driven V o diffusion and the physisorbed CO 2 configurations. Our combined results unravel the critical role of defect sites on TiO 2 in determining the elementary step of CO 2 activation during chemical reactions.