What is it about?

We present a Density Functional Theory (DFT) investigation on the adsorption of H2O on ultra-thin TiO2 layers supported on TiN. Charge transfer from TiN leads to the formation of reduced Ti3+ cations in TiO2, which is proportionally higher compared to interfacial models with thicker oxide layers. Fully water covered stoichiometric models are stable at typical ambient conditions. In contrast, interfacial models with multiple vacancies are most stable at low (reducing) oxygen chemical potential values. H2O adsorbs dissociatively on the highly distorted 2-layer TiO1.75–TiN interface, where the Ti3+ states lying above the top of the valence band contribute to a significant reduction of the energy gap compared to the stoichiometric TiO2–TiN model.

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Why is it important?

In previous works, we studied interfacial systems with thicker oxide layers supported on TiN. We observed that the surface keeps the rutile symmetry and H2O is preferentially adsorbed in molecular form. This behaviour is similar to that observed on pure TiO2 surfaces. In contrast, interfacial models with multiple vacancies are most stable in models with ultra-thin oxide layers. The high concentration on reduced Ti3+ introduces significant distortions in the O-defective slab, causing the spontaneous dissociation of water, and the Ti3+ states lying above the top of the valence band contribute to a significant reduction of the energy gap compared to the stoichiometric TiO2–TiN.

Perspectives

Our results provide a guide for the design of novel interfacial systems containing ultra-thin TiO2 with potential application as photocatalytic water splitting devices.

Dr Julio Gutiérrez Moreno
Barcelona Supercomputing Center

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This page is a summary of: Structure, stability and water adsorption on ultra-thin TiO2 supported on TiN, Physical Chemistry Chemical Physics, January 2019, Royal Society of Chemistry, DOI: 10.1039/c9cp04506f.
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