Facet-dependent trapping and dynamics of excess electrons at anatase TiO2 surfaces and aqueous interfaces

Abstract

Excess electrons from intrinsic defects, dopants and photoexcitation play a key role in many of the properties of TiO2. Understanding their behaviour is important for improving the performance of TiO2 in energy-related applications. We focus on anatase, the TiO2 polymorph most relevant in photocatalysis and solar energy conversion. Using first-principles simulations, we investigate the states and dynamics of excess electrons from different donors near the most common anatase (101) and (001) surfaces and aqueous interfaces. We find that the behaviour of excess electrons depends strongly on the exposed anatase surface, the environment and the character of the electron donor. Whereas no electron trapping is observed on the (101) surface in vacuo, an excess electron at the aqueous (101) interface can trigger water dissociation and become trapped into a stable surface Ti(3+)-bridging OH complex. By contrast, electrons avoid the (001) surface, indicating that oxidation reactions are favoured on this surface. Our results provide a bridge between surface science experiments and observations of crystal-face-dependent photocatalysis on anatase, and support the idea that optimization of the ratio between {101} and {001} facets could provide a way to enhance the photocatalytic activity of this material.

Effect of reducible oxide–metal cluster charge transfer on the structure and reactivity of adsorbed Au and Pt atoms and clusters on anatase TiO2

“…The use of a simple GGA to model reduced anatase is justified by the fact that excess electrons are typically quite delocalized in this material. 46,48 In addition, extensive test calculations including an on-site Hubbard U term (U = 3.3 or 3.9 eV) on the Ti3d states showed trends qualitatively very similar to those obtained with a pure GGA (see the supplementary material for Table S2). We also notice that the GGA-PBE functional does not include van der Waals (vdW) dispersion interactions that have been reported to introduce significant corrections to the computed adsorption energies of metal clusters on TiO 2 in a recent study.…”

“…39 Characteristic features of anatase (101) in comparison to the well-studied rutile TiO 2 (110) surface are that oxygen vacancies reside (well) below the surface 44,45 and excess electrons form poorly localized polaronic states with energy levels in the band gap close to the conduction band (CB) edge. [46][47][48][49] Previous investigations have found that step edges may serve as nucleation sites for the growth of Pt clusters on anatase (101) 50 and 3D Pt structures are preferred on this surface. 51 It was also shown that the interaction of Au clusters with anatase (101) is weaker than that of Pt clusters, 5 and the contributions of van der Waals (vdW) forces can be significant.…”

Engineering oxygen vacancy on rutile TiO2 for efficient electron-hole separation and high solar-driven photocatalytic hydrogen evolution

“…Hence, photocatalytic hydrogen production attracts much more attention recently [2][3][4]. Since Fujishima and Honda [5][6][7] discovered hydrogen production from water splitting on TiO 2 for the first time, it is considered as the most promising photocatalyst candidate due to nontoxicity, high stability and low-cost [8][9][10]. Therefore, TiO 2 is widely used in photocatalytic degradation of pollutants, photocatalytic hydrogen production, solar cells, photoelectrochemical devices, and so on [11][12][13][14].…”

Theoretical Studies of Titanium Dioxide for Dye-Sensitized Solar Cell and Photocatalytic Reaction

“…For example, based on the Hubbard-corrected DFT + U and first-principles molecular dynamics (FPMD) simulations, facet-dependent trapping and dynamics of excess electrons at anatase TiO 2 surfaces and aqueous interfaces could be achieved. Whereas no electron trapping is observed on the (101) surface in vacuo, an excess electron at the aqueous (101) interface can trigger water dissociation and become trapped into a stable surface Ti 3+ -bridging OH complex [30].…”