Kinetic Control of Oxygen Interstitial Interaction with TiO₂(110) via the Surface Fermi Energy

Atomically clean surfaces of semiconducting oxides efficiently mediate the interconversion of gas-phase O₂ and solid-phase oxygen interstitial atoms (O_i). First-principles calculations together with mesoscale microkinetic modeling are employed for TiO₂(110) to determine reaction pathways, assess appropriate rate expressions, and obtain corresponding activation energies and pre-exponential factors. The Fermi energy (E_F) at the surface influences the rate-determining step for both injection and annihilation of O_i. The barriers range between 0.72-0.82 eV for injection and 0.60-2.34 eV for annihilation and may be manipulated through intentional control of E_F. At equilibrium, the microkinetic model and first-principles calculations indicate that interconversion of O_i species in the first and second sublayers limits the rate. The effective pre-exponential factors for injection and annihilation are surprisingly low, probably resulting from the use of simple Langmuir-like rate expressions to describe a complicated kinetic sequence.