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

Area of Science:

• Materials Science
• Surface Chemistry
• Catalysis

Background:

• Molecular-level understanding of TiO2 and CO2 interactions is vital for CO2 reduction into energy sources.
• Defect sites on TiO2 surfaces significantly influence chemical reaction pathways.

Purpose of the Study:

• To investigate the CO2 activation process on reduced TiO2(110) surfaces at room temperature.
• To elucidate the role of oxygen vacancies in CO2 dissociation and surface interactions.

Main Methods:

• In situ ambient pressure scanning tunneling microscopy (AP-STM) for real-time surface observations.
• Synchrotron-based ambient pressure X-ray photoelectron spectroscopy (AP-XPS) for surface oxidation state analysis.
• Density functional theory (DFT) calculations to model reaction mechanisms.

Main Results:

• Oxygen vacancies (Vo) dynamically diffuse along bridging oxygen rows on TiO2(110) under CO2.
• CO2 dissociation leads to oxygen abstraction, occupying Vo sites and facilitating diffusion.
• TiO2 surfaces without vacancies exhibit only CO2 physisorption on Ti4+ sites.
• AP-XPS confirmed changes in surface oxidation states due to Vo healing or CO2 physisorption.
• DFT calculations provided insights into CO2-driven Vo diffusion and physisorbed configurations.

Conclusions:

• Defect sites, specifically oxygen vacancies, play a critical role in the initial CO2 activation step on TiO2 surfaces.
• The dynamic diffusion of oxygen vacancies is a key phenomenon in CO2 interaction with reduced TiO2(110).
• This study provides a molecular-level understanding of CO2 activation, crucial for designing efficient catalysts for CO2 conversion.