Coordination of Ti⁴⁺ Sites in Nanocrystalline TiO₂ Films Used for Photoinduced Electron Conduction: Influence of Nanoparticle Synthesis and Thermal Necking

Abstract

Nanocrystalline titania (TiO 2 ) anatase films are widely utilized as substrates for electron conduction in photoelectrochemical devices. In this paper, we subjected the lattice disorder of TiO 2 anatase nanoparticles and the resulting nanocrystalline films to analysis with X-ray absorption fine structure spectroscopy. The TiO 2 nanoparticles were synthesized from dehydration of a titanate and from a conventional sol-gel method. Although both specimens had similar first shell Ti 41 coordination numbers (CNs) of ca. 5.7, the titanate-derivative TiO 2 was shown to be phase-pure anatase and the sol-gel TiO 2 contained a minute amount of brookite impurity. After nanoparticle necking into films, the former TiO 2 exhibited a negligible decrease in the CN, whereas the latter showed a significant decrease to a value of ca. 4.9. As a result, the titanate-derivative film is more efficient than the sol-gel one in transmitting electrons injected from a photoexcited dye. Significant lattice distortion near the grain boundaries of films are believed to occur during necking of the nanoparticles containing impurities. We have demonstrated that the synthesis of phase-pure nanoparticles is essentially important in fabricating films with a minimal degree of lattice disorder.

Heterojunction BiVO4/WO3 electrodes for enhanced photoactivity of water oxidation

“…Since the first demonstration of this concept in 1972, 1 much attention has been paid to semiconductor materials which could be used as photoelectrodes. [2][3][4] Although TiO 2 is the first and the most studied anode material employed for the PEC cell, [5][6][7] its large band gap of 3.2 eV absorbing only UV part of the solar spectrum is a significant drawback in practical application for solar hydrogen production. Thus, recent research has focused on the development of visible light-active materials.…”

Formation of single-crystalline TiO2 nanomaterials with controlled phase composition and morphology and the application in dye-sensitized solar cell

“…The conversion efficiency of the dye-sensitized solar cell based on the nanoparticles was increased by over 40% compared to that of the cell based on P25. Teng and co-workers [38][39][40] also synthesized anatase nanoparticles by hydrothermal treatment of H-titanate nanotubes, and applied it to dye-sensitized solar cells. Their studies focused on the charge transport in the nanoporous TiO 2 film.…”

“…The efficiency of collecting the injected electron is determined by the charge transport rate and the electron lifetime [38][39][40]. The light harvesting efficiency is determined by the BET surface area, the amount of the dye adsorbed and optical absorption properties of the porous TiO 2 films.…”

Formation of internal p–n junctions in Ta3N5photoanodes for water splitting

“…15,55,56 We subjected the Ta 3 N 5 and Ta 3 N 5 :Co lms to analysis with IMPS, which measures the photocurrent response to modulation in incident light intensity. [57][58][59] During the IMPS measurements, the Ta 3 N 5 and Ta 3 N 5 :Co electrodes were biased at 0.5 V (vs. Ag/AgCl) and illuminated with a blue light-emitting diode (l max ¼ 455 nm) at 15 mW cm À2 . Fig.…”