Insights into How Fluorine-Adsorption and n‑Type Doping Affect the Relative Stability of the (001) and (101) Surfaces of TiO₂: Enhancing the Exposure of More Active but Thermodynamically Less Stable (001)

The stability of both the pure and fluorine (F)-adsorbed surface of TiO₂ is examined on the basis of density functional calculations. For pure surfaces, both the beneficial local geometric structures and local potential strengthen the Ti–O binding in (101), rendering it the most stable surface. For F-adsorbed surfaces, F-adsorption significantly weakens the Ti–O bonds in (101) but strengthens them in (001), so that (001) becomes more stable than (101) for the F-adsorbed surfaces. On the basis of this observation, we further show that the n-type doping in TiO₂ can significantly decrease the ability of F-adsorption in switching the relative stability of the two surfaces. The present work not only provides new insights into the physical and chemical properties about both pure and F-adsorbed surfaces of TiO₂ and conclusively explains related experimental results but also suggests viable ways to prepare TiO₂ samples with a high percentage of (001)