<p></p><p>Interfacial metal-oxide systems with ultrathin oxide layers
are of high interest for their use in catalysis. In
this study, we present a density functional theory (DFT) investigation of the structure
of ultrathin rutile layers (one and two TiO<sub>2</sub> layers) supported
on TiN and the stability of water on these interfacial
structures. The rutile layers are
stabilized on the TiN surface through the formation of interfacial Ti–O bonds.
Charge transfer from the TiN substrate leads to the formation of
reduced Ti<sup>3+</sup> cations in TiO<sub>2.</sub> The structure of the one-layer oxide slab is strongly
distorted at the interface, while the thicker TiO<sub>2</sub> layer preserves
the rutile structure. The energy cost for the formation of a single O vacancy
in the one-layer oxide slab is only 0.5 eV with respect to the ideal interface.
For the two-layer oxide slab, the introduction of several vacancies in an already non-stoichiometric
system becomes progressively more
favourable, which indicates the stability of the
highly non-stoichiometric interfaces. Isolated water molecules dissociate when
adsorbed at the TiO<sub>2</sub> layers. At higher coverages the preference is
for molecular water adsorption. Our ab initio thermodynamics calculations show the fully water covered stoichiometric
models as the most stable structure at typical ambient conditions. Interfacial
models with multiple vacancies are most
stable at low (reducing) oxygen chemical potential values. A water monolayer adsorbs dissociatively on the highly distorted 2-layer
TiO<sub>1.75</sub>-TiN interface, where
the Ti<sup>3+</sup>
states lying above the top of the valence band contribute to a significant
reduction of the energy gap compared to the stoichiometric TiO<sub>2</sub>-TiN
model. Our results provide a guide for the design of novel interfacial systems containing
ultrathin TiO<sub>2</sub> with potential application as photocatalytic water
splitting devices.</p><p></p>
Ethanol and Water Adsorption in Conventional and Hierarchical All-Silica MFI Zeolites
