Effect of Hydrogen Treatment on Anatase TiO₂Nanotube Arrays for Photoelectrochemical Water Splitting

Abstract

Hydrogen (H 2 ) treatment using a two-step TiO 2 nanotube (TONT) film was performed under various annealing temperatures from 350 ºC to 550 ºC and significantly influenced the extent of hydrogen treatment in the film. Compared with pure TONT films, the hydrogen-treated TONT (H:TONT) film showed substantial improvement of material features from structural, optical and electronic aspects. In particular, the extent of enhancement was remarkable with increasing annealing temperature. Light absorption by the H:TONT film extended toward the visible region, which was attributable to the formation of sub-band-gap states between the conduction and valence bands, resulting from oxygen vacancies due to the H 2 treatment. This increased donor concentration about 1.5 times higher and improved electrical conductivity of the TONT films. Based on these analyses and results, photoelectrochemical (PEC) performance was evaluated and showed that the H:TONT film prepared at 550 ºC exhibited optimal PEC performance. Approximately twice higher photocurrent density of 0.967 mA/cm 2 at 0.32 V vs. NHE was achieved for the H:TONT film (550 ºC) versus 0.43 mA/cm 2 for the pure TONT film. Moreover, the solar-to-hydrogen efficiency (STH, η) of the H:TONT film was 0.95%, whereas a 0.52% STH efficiency was acquired for the TONT film. These results demonstrate that hydrogen treatment of TONT film is a simple and effective tool to enhance PEC performance with modifying the properties of the original material.

Electrochemical Fabrication of Ternary Black Ti‐Mo‐Ni Oxide Nanotube Arrays for Enhanced Photoelectrochemical Water Oxidation

“…Hydrogen, as a reducing atmosphere, can highly facilitate the gas diffusion into the titanium dioxide lattice structure and also prevents the solvent incorporation within the lattice . In this context, creating favorable defects in the material by annealing in reducing atmosphere, is another promising strategy to reinforce the performance of metal oxide photoanodes . Indeed, many hypotheses have confirmed that treating Ti‐based alloys in reducing atmospheres can considerably introduce oxygen vacancies with low formation energy .…”

“…To this end, several studies reported the influence of hydrogen annealing on the activity of titania (TiO 2 : H) at high temperatures (350‐550 °C) for various durations. It was reported that annealing under hydrogen leads to the creation of defect states below the CB, thus reducing the band gap of TiO 2 and further extending its optical activity in the visible spectrum . Additionally, some reports have pointed out that hydrogen treatment could contribute to enhancing the photocurrent of the fabricated material due to its ability to passivate the surface defect states …”

Improved Charge Carrier Transport of Hydrogen-Treated Copper Tungstate: Photoelectrochemical and Computational Study

“…24 Hydrogen-treatment can reduce metal oxide semiconductor materials by introducing oxygen vacancies and hydrogen impurities and thus is a simple method to increase the donor density and electrical conductivity. In recent years, several common photoanodes, TiO 2 , [25][26][27][28][29][30] α-Fe 2 O 3 , 31,32 WO 3 , 33 and BiVO 4 , 34,35 have been treated using this method and resulted in photocurrent density enhancement. By analogy, in this work, the annealed electrodeposited CuWO 4 films were further thermally treated under an atmosphere of 5% hydrogen in argon.…”

Modified photo-electrochemical and photo-voltaic properties of solvothermally crystallised TiO2 nanotube arrays

“…From the Mott-Schottky plot, the slope of C sc -2 versus V gives the donor density. The donor density values are estimated from these plots and are found to be 1.2 9 10 18 and 1.8 9 10 17 cm -3 for S-TNT and TNT sample respectively [24]. The variation of donor density by an order of magnitude reflects the higher density of oxygen vacancy defects and corroborates the results of XPS, EPR and PL spectroscopy studies.…”