DFT investigation on the adsorption of H2O at ultra-thin TiO2 layers supported on TiN

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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Photo by Eliška Motisová on Unsplash

Photo by Eliška Motisová on Unsplash

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.

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