Reactions of fluid and lattice oxygen mediated by interstitial atoms at the TiO2(110)-water interface

초록

O2 interacts with TiO2 surfaces in numerous aqueous reactions for clean hydrogen production, wastewater cleanup, reduction of CO2 and N2, and O2 sensing. In many cases, these reactions involve reversible exchange of O with the solid, whose participation is usually thought to require oxygen vacancies (VO). Based on measurements of oxygen isotopic self-diffusion in rutile TiO2 under water, this work proposes a different perspective centered on O interstitial atoms (Oi). Experiments with varying concentrations of O2 and mole fractions of 18O show that the (110) surface facilitates O exchange with both the H2O liquid and its dissolved O2. First-principles calculations indicate that on-top and "surface Oi" configurations of adsorbed O participate sequentially in the exchange process. Adsorbed OH appears to provide a single pathway for H2O and O2 to contribute oxygen, although fitting the diffusion data to simple models indicates that H2O contributes more. Because rutile TiO2 is a prototypical metal oxide, this picture based on Oi probably generalizes in many cases to other oxides - explaining important aspects of their thermal, electrochemical, and photochemical reactions with dissolved O2.

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