Photooxidation of Water on Pristine, S- and N-Doped TiO₂(001) Nanotube Surfaces: A DFT + U Study

Abstract

Using density functional theory calculations, we study the structure, energetics, and the photoelectrochemical oxidation of water on pristine, S-, N-, and (N + S)-doped anatase TiO2(001) nanotube (NT) surfaces. We found that water adsorbs molecularly on pristine and S-doped surfaces, while N doping promotes dissociative adsorption (both in the presence and absence of the S codopant) and leads to more favorable adsorbate–substrate interactions. Under photoelectrochemical conditions, OH groups are the most stable species on each surface with decreasing stability in the sequence (N + S) ≈ N → S → pristine. Surface Ti5C are the active sites and the anion impurity sites are not structurally affected during the water oxidation reaction. Nanostructuring TiO2 by forming three monolayer-thick (3 ML) TiO2(001) NT surfaces and subsequent anion doping yield an overpotential drop from 1.31 V on the flat (2D) TiO2(001) surface to 0.90, 0.71, 0.94, and 0.96 V on pristine, S-, N-, and (N + S)-doped nanotube surfaces, respectively. This reduction is a consequence of the strain-induced weakening of hydroxyl adsorption on the NT surfaces; the presence of an N dopant atom does not change the overpotential relative to the pristine nanotube, irrespective of the presence of a codoped S atom, while single S doping produces a slight decrease of the overpotential by 0.2 V. In all cases, the overpotential-determining step is the hydroxyl group dehydrogenation.

Origin of photocatalytic activity enhancement in Pd/Pt-deposited anatase N-TiO2 – experimental insights and DFT study of the (001) surface

“…13,14 Density functional theory (DFT)+U study revealed that N-doping promotes dissociative water adsorption, leading to favorable adsorbate-substrate interactions and stabilization of OH groups at the TiO 2 surface. 15 Therefore, combined metal modification and non-metal doping is a good approach for catalyst tailoring. [16][17][18] This, however, should be treated carefully, since dopants introduced in the TiO 2 lattice can have states near the conduction band (CB), allowing the formation of mid-gaps that can accelerate electron-hole recombination rates and hinder photocatalytic performance.…”

Interfacial Charge Transport in 1D TiO2 Based Photoelectrodes for Photoelectrochemical Water Splitting

“…[ 193 ] While solo N dopant hardly optimize the photoinduced water oxidation kinetics compared with S dopant, but the S and N codoping method can improve the PEC performance of TiO 2 effectively by means of lowering the required energy. [ 188,194 ] s discussed in Sections 2 to 5, the multihierarchical composited TiO 2 photoelectrodes show better PEC performance as well as optical response to visible lights due to the interior heterojunction interfaces induced built‐in electric field, as well as the exterior designed nanoarchitectures and photoabsorbers (or cocatalysts).…”

“…N, S, B, F, and P dopants can shift the VB of TiO 2 toward water oxidation potential, while these shallow acceptor doping would trigger electron mobility recession owing to the electronic attraction of acceptor dopants. [188][189][190][191][192] According to the research of Asahi et al, N is the most suitable dopant to form new energy state well overlapped with O 2p orbital leading to proceed visible lights induced water oxidation with stable microstructure. [183] With the introduced oxygen defects and Ti 3+ color centers in N doped TiO 2 , N doped TiO 2 show good progress on visible lights harvest and electronic conductivity.…”

2D Slab Models of Nanotubes Based on Tetragonal TiO2 Structures: Validation over a Diameter Range

“…This included a study of water adsorption on 2D-representation of 9-layered TiO 2 nanotube, on clean and doped surfaces [ 9 ]. The CFVS model was also used to study the structure, energetics, and the photoelectrochemical oxidation of water on the aforementioned structures by means of the DFT + U method and a plane-wave-based computational code Quantum Espresso [ 10 , 11 ]. The results of these studies are summarized in a review [ 12 ].…”