Hydrogenated TiO₂ nanotube photonic crystals for enhanced photoelectrochemical water splitting

Abstract

We report the design, fabrication and characterization of novel TiO nanotube photonic crystals with a crystalline core/disordered shell structure as well as substantial oxygen vacancies for photoelectrochemical (PEC) water splitting. The novel TiO nanotube photonic crystals are fabricated by annealing of anodized TiO nanotube photonic crystals in hydrogen atmosphere at various temperatures. The optimized novel TiO nanotube photonic crystals produce a maximal photocurrent density of 2.2 mA cm at 0.22 V versus Ag/AgCl, which is two times higher that of the TiO nanotube photonic crystals annealed in air. Such significant PEC performance improvement can be ascribed to synergistic effects of the disordered surface layer and oxygen vacancies. The reduced band gap owing to the disordered surface layer and localized states induced by oxygen vacancies can enhance the efficient utilization of visible light. In addition, the disordered surface layer and substantial oxygen vacancies can promote the efficiency for separation and transport of the photogenerated carriers. This work may open up new opportunities for the design and construction of the high efficient and low-cost PEC water splitting system.

Influence of Annealing Atmospheres on Photoelectrochemical Activity of TiO2 Nanotubes Modified with AuCu Nanoparticles

“…41 Treatment in different atmospheres leads to a reduction of the band gap, and this can be attributed to the localized states induced by oxygen vacancies or disordered surface layers. 42 Annealing in vacuum, argon, and hydrogen causes the removal of oxygen atoms and generates oxygen vacancies surrounded by Ti cations in the Ti 3+ or Ti 2+ valence state. 43,44 Moreover, the vacuum treatment decreases the structural order of TiO 2 .…”

Black 3D-TiO2 Nanotube Arrays on Ti Meshes for Boosted Photoelectrochemical Water Splitting

“…However, its PEC performances are still inhibited by the large bandgap (3.2 eV), which results in the photoexcited electron and hole not being produced by the visible light harvested by the 3D NTAs [30][31][32][33][34][35][36][37]. In addition, 3D-TiO 2 NTAs also suffer from poor electrical conductivity, and the bulk and surface recombination of photogenerated charge carriers, both of which are detrimental to the PEC water splitting activity [37][38][39][40][41]. Consequently, seeking an efficient strategy to boost the utilization of visible light and the electrical conductivity is vitally crucial.…”

“…As illustrated by many research groups, the introduction of the O-vacancies can enable the Fermi energy level to shift toward the conduction band, which leads to the shrinkage of the bandgap, thus promoting the utilization efficiency of the visible light [31,[41][42][43][44]. In addition, the presence of O-vacancies can also increase the electrical conductivity due to the high donor density, which facilitates the separation and transport of photogenerated charge carriers [31,38,39,44]. Accordingly, it is anticipated that rational introduction of the O-vacancies in 3D-TiO 2 NTAs may be a promising route to tackle the two abovementioned drawbacks.…”

“…Accordingly, it is anticipated that rational introduction of the O-vacancies in 3D-TiO 2 NTAs may be a promising route to tackle the two abovementioned drawbacks. Unfortunately, the reported available strategies to produce O-vacancies generally involve the harsh experimental conditions or high-cost facilities, which are not suitable for the largescale practical application [31,38,39,44]. Hence, exploiting a simple and economical method to introduce O-vacancies into metal oxide still requires more endeavors.…”

Transparent Stacked Photoanodes with Efficient Light Management for Solar-Driven Photoelectrochemical Cells

“…To maximize carrier generation, researchers have adopted nanoscale structures to increase optical absorption and carrier-collection efficiency. Various nanoscale structures, such as nanorods, two-dimensional (2D) porous films, and petals, ,− have been used to fabricate PECs. However, limitations inherent in large-scale processing remain a serious obstacle blocking the industrialization of nanoscale PEC systems.…”