Oxyfluoride Pb₂Ti₄O₉F₂ as a Stable Anode Material for Photoelectrochemical Water Oxidation

Abstract

An oxyfluoride, Pb 2 Ti 4 O 9 F 2 , was examined as an electrode material for water splitting, and the electrochemical band edge potentials were compared with those of an analogous oxide, Bi 2 Ti 4 O 11 . Pb 2 Ti 4 O 9 F 2 with a band gap of 3.0 eV, which is slightly smaller than that of Bi 2 Ti 4 O 11 (3.1 eV), worked as an n-type semiconductor anode for water oxidation upon band-gap photoexcitation (λ < 420 nm) in the presence of a CoO x cocatalyst to produce O 2 without noticeable degradation. Mott−Schottky analysis and photocurrent onset potential measurement showed that the flat-band potential of Pb 2 Ti 4 O 9 F 2 was positioned at around −0.5 V versus NHE at pH 7.0, which was 0.2 V more negative than that of Bi 2 Ti 4 O 11 . Results of physicochemical analyses, together with previous first-principles calculations, suggest that the relatively negative flat-band potential of Pb 2 Ti 4 O 9 F 2 is due to the stronger orbital interaction between Pb-6s and O-2p in the valence band than that between Bi-6s and O-2p in Bi 2 Ti 4 O 11 because the difference in the orbital energy between metal-6s and O-2p is smaller in the former than in the latter. This stronger Pb-6s/O-2p interaction increases the valence band maximum and conduction band minimum, which causes Pb 2 Ti 4 O 9 F 2 to be operable as a photoanode at lower applied potential. The O-2p orbitals that constitute the valence band maximum of Pb 2 Ti 4 O 9 F 2 also appear to be essential for the realization of stable water oxidation to form O 2 .Article pubs.acs.org/JPCC

Structural Properties of NdTiO2+xN1–x and Its Application as Photoanode

“…As a consequence, the modified FTO/NdTiO 2+ x N 1– x /Nb 2 O 5 electrode yielded noticeable anodic photocurrent compared to the as-deposited FTO/NdTiO 2+ x N 1– x photoelectrode. It should be mentioned that similar effects have been observed on Pb 2 Ti 4 O 9 F 2 , Pb 2 Ti 2 O 5.4 F 1.2 , and TaON particle-based thin film photoanode by modifying with Ta 2 O 5 or TiO 2 driving from TaCl 5 or TiCl 4 . ,, …”

“…A NbCl 5 impregnation step, which was adapted from TaCl 5 and TiCl 4 , , was performed to improve the connection of particles. The FTO/NdTiO 2+ x N 1– x photoelectrode was soaked in 0.1 M NbCl 5 (99.99 wt %, abcr GmbH) dissolved in ethanol for 10 s and dried on a hot plate at 423 K. After repeating this procedure for four rounds, the electrode was then annealed in air at 573 K for 1 h to obtain FTO/NdTiO 2+ x N 1– x /Nb 2 O 5 .…”

Recent Progress in Mixed‐Anion Materials for Solar Fuel Production

“…A photoanode made from Pb 2 Ti 4 O 9 F 2 operating under UV irradiation ( λ < 400 nm) also showed very stable behavior in water oxidation. [ 106 ]…”

Structural Properties of NdTiO2N and Its Application as Photoanode

“…The FTO/NdTiO2N photoanodes were dried naturally in air. A NbCl5 impregnation step, which was adapted from TaCl5 and TiCl4, [15,23] was performed to improve the connection of particles. The FTO/NdTiO2N photoelectrode was soaked in 0.1 M NbCl5 (99.99 wt %, abcr GmbH) dissolved in ethanol for 10 seconds, and dried on a hot plate at 423 K. After repeating this procedure for four rounds, the electrode was then annealed in air at 573 K for 1 hour to get FTO/NdTiO2N/Nb2O5.…”