Excess Electrons and Interstitial Li Atoms in TiO₂ Anatase: Properties of the (101) Interface

Abstract

Lithium intercalation across the anatase (101) surface is investigated with hybrid DFT. It is demonstrated that the upper surface layers of the oxide are geometrically less constrained, allowing stabilization of both excess electrons (by 5 × 10 −2 eV) and intercalated Li + cations (by 1.1 × 10 −1 ) eV compared to bulk anatase. Li + ions tend to segregate in the first subsurface layers, forming rows along the [010] crystal direction. Also, excess electrons localize preferentially subsurface, as confirmed by these hybrid and additional random phase approximation (RPA) calculations. Furthermore, subsurface Li + ions act as pinning centers for adsorbates, stabilizing them by roughly 1.1 × 10 −1 eV, with some variations depending on the adsorption geometry and on the vicinity of the cations. The cation incorporation mechanism in the oxide is also affected by the presence of the interface: The two step Li + insertion process has an activation energy of 1.43 eV, more than double the activation energy for cation migration in bulk systems. A monolayer of acetonitrile solvent on top of the slab facilitates the process, lowering the barrier to 7.6 × 10 −1 eV. The interaction between Li + ions and electrons is also stronger at the (101) interface and can be quantified in 9 × 10 −2 eV, more than double that of its bulk value. The combined effect of adsorbate pinning and enhanced electron localization constitute a reservoir of shallow trap states in the proximity of the adsorbed donor molecules, likely to facilitate charge-transfer mechanisms. In contrast, the magnitude of the Li + /electron interaction, even if enhanced at the interface, is still low enough to allow subsequent charge migration toward other acceptor centers in the oxide, likely with a mechanism spanning different time scales.

Influences of Doping on Photocatalytic Properties of TiO2 Photocatalyst

“…Recently, many researchers found that lithium (Li) doping plays an important role in the inhibition of activity in the TiO 2 network acting as an electron trapping or hole trapping [239][240][241]. Bouattour et al reported Li-doped TiO 2 nanoparticles through a sol-gel process and investigated their potential application as a photocatalyst for degradation of different organic compounds [240].…”

Assessment of Density Functional Theory in Predicting Interaction Energies between Water and Polycyclic Aromatic Hydrocarbons: from Water on Benzene to Water on Graphene

“…51 Thus, RPA is increasingly used as a cost-efficient first-principles method for 4 modeling noncovalent interactions in molecules and materials. [52][53][54][55][56][57][58] Nevertheless, RPA underestimates dispersion energies 47 as a result of lacking higher excitations and density-driven error 59 inherited from the semilocal Kohn-Sham reference. The latter can be ameliorated by variational selfconsistent RPA 60 or perturbative singles corrections.…”

On the Stability Issues of TiO2-Based Composites in View of Fuel Cell Application: A Combined Experimental and Theoretical Investigation

“…Previous experimental and theoretical works performed on TiO 2 bulk and surfaces clearly indicate that Li atoms can intercalate in the distorted octahedral cavities of TiO 2 with a charge transfer from the intercalated Li atom to a Ti site. − As concerns in the theoretical studies, it is important to stress that pure DFT approaches fail to reproduce the electrochemical behavior of such systems due to the well-known self-interaction error found in pure LDA or GGA functionals, , contaminating the band gap and description of electron localization properties. Previous works have been indeed mainly performed with recurring molecular mechanics, HF, and DFT+U and more recently, hybrid DFT , methods, as done here. The electrochemical insertion process can be schematically described as indicated by the following equation where x is the mole fraction of lithium into TiO 2 .…”

“…Figure shows the three most stable positions found for a neutral interstitial Li atom (Li i ) at the TiO 2 –LiKCO 3 interface: Li 1 corresponds to the most stable top-surface adsorption site, while Li 2 and Li 3 are two different subsurface configurations. Since cavities in deeper surface layers were already found to behave like bulklike layers where Li intercalation is less favorable, these insertion sites were not considered. Analogous configurations were also identified for the clean TiO 2 -(101) surface.…”