Electronic Structure of Pure and N-Doped TiO₂ Nanocrystals by Electrochemical Experiments and First Principles Calculations

Abstract

Optical and electrochemical characterizations are carried out in conjunction with first-principles calculations on pure and N-doped titania nanocrystals. These are prepared in laboratory with initial doping concentrations of triethylamine in the range of 0.1-0.5 N/Ti molar ratio. Diffuse reflectance UV-vis spectra of N-doped samples present a significant absorption in the visible region. The flatband potential (E fb ) of pure and nitrogen-doped TiO 2 (-0.6 ( 0.2 V vs NHE) is determined by impedance spectroscopy (Mott-Schottky plots) and the quasi-Fermi level, n E F * (-0.67V vs NHE) by photovoltage measurements as a function of the suspension pH in the presence of an electrochemical probe (methylviologen, MV 2þ ). Theoretical density of electronic states calculations, where several N doping versus vacancy combinations are taken into consideration, together with the optical and electrochemical experiments allow us to draw a detailed picture of the electronic features of the doped samples.

Effect of N-doping on the photocatalytic activity of sol–gel TiO2

“…However there now appears to be some agreement regarding the fine electronic details of N doped visible light absorption as reported by Irie [8] and Nakamura [9]. It is now believed that oxygen lattice sites within the TiO 2 crystal are substituted by nitrogen atoms [10,11] form an occupied midgap (N 2p) level above the TiO 2 (O 2p) valence band. The N 2p band therefore acts as a step between the valence and the conduction band of the semiconductor, facilitating excitation of electrons from the N 2p mid-gap band to the conduction band upon irradiation with visible light [8,9].…”

Niobium addition enhancing the corrosion resistance of nanocrystalline Ti5Si3 coating in H2SO4 solution

“…In contrast, at potentials more positive than E fb , the band bending creates a barrier (space charge layer) to electron transfer, and the sample shows a dielectric characteristic. Although a precise determination of the flat band potential is often complicated by the presence of surface states and defects unavoidably connected with the nanometer size of the passive film [75,76], the information on E fb provides useful guides to the understanding of electrochemical behavior. Many researchers have demonstrated that there was an intrinsic relationship between the localized corrosion resistance and the flat band potential of the passive film [77][78][79].…”

Visible Light Water Splitting via Oxidized TiN Thin Films

“…30 For our samples, we measured open circuit voltages between -0.5 V and -0.7 V, which depended on the deposition pressure and annealing time/temperature. In general, the asdeposited films had slightly lower open circuit voltages, and as the annealing time increased, so did the open circuit voltage.…”