Enhanced Performance of Pristine Ta₃N₅ Photoanodes for Solar Water Splitting by Modification with Fe–Ni–Co Mixed-Metal Oxide Cocatalysts

Abstract

Solar water splitting is an alternative way of clean and sustainable hydrogen production. Tantalum nitride (Ta 3 N 5 ) is one of the promising candidates that recently attracted a great amount of attention as photoelectrodes for solar water splitting. Nevertheless, it suffers severely from photocorrosion in an aqueous solution. Therefore, the precise selection of a cocatalyst, in terms of the material, the amount, and the way of its deposition, is indispensable to highly improve its water splitting performance. In the present work, we introduce a Fe−Ni−Co mixed-metal oxide as a water oxidation cocatalyst that remarkably improved the photocurrent and photostability of the pristine Ta 3 N 5 photoanode. The cocatalyst-modified electrode showed a photocurrent of about 4.0 mA cm −2 at 1.23 V vs RHE in 1 M NaOH. The electrode maintained 100% and 96% of the initial photocurrent after irradiation times of 1 and 2 h, respectively. In addition, a continuous evolution of hydrogen and oxygen occurred for 2 h at quantitative Faraday efficiencies (>96%). This photostability is superior compared to that of the other singlelayer modified Ta 3 N 5 photoanodes reported so far. It is noteworthy that the anodic spark deposition is used to fabricate precursor electrodes (NaTaO 3 ), which then were converted to Ta 3 N 5 by nitridation in an ammonia atmosphere.

Preparation of Nanostructured Ta3N5 Electrodes by Alkaline Hydrothermal Treatment Followed by NH3 Annealing and Their Improved Water Oxidation Performance

“…In summary, the NaTaO 3 precursor were prepared in a pure NaOH aqueous solution (23 wt %) at 250 °C for 5 h, at higher temperature and longer reaction time than those of the reported ones. 25−27 These conditions gave the best PEC water oxidation performance among the others, after the conversion to the corresponding Ta 3 N 5 and modification with the cocatalyst. To the best of our knowledge, the present study is the first report of the preparation of nanostructured Ta 3 N 5 photoanodes through the hydrothermal method in a F – -free alkaline solution.…”

“…A voltage sweep voltammetry (in a range of 0.1–0.5 V vs Ag/AgCl) was applied for five cycles under light with the intensity of 100 mW cm –2 . 25…”

“…In our recent publication, we utilized the anodic spark deposition (ASD), which is a facile technique, to fabricate a highly active and a tightly adhesive Ta 3 N 5 layer on the Ta substrate. 25 However, the control on the surface morphology of the resultant electrodes is still challenging in the use of the ASD.…”

“…As another way, hydrothermal treatment of Ta metal in alkaline solutions has been reported to prepare (Ta, Na)O x 25−27 and (Ta, K)O x . 28 Generally, Ta oxide formation from metal Ta requires a higher concentration of bases and elevated temperature.…”

Transparent Ta3N5 Photoanodes for Efficient Oxygen Evolution toward the Development of Tandem Cells

“…The fabrication of transparent Ta 3 N 5 films is not a trivial task, largely due to the extreme conditions required to prepare Ta 3 N 5 . Ta 3 N 5 ‐based photoanodes are typically processed by heating Ta precursor compounds in an NH 3 atmosphere at high temperatures (close to 1000 °C) ,. Unfortunately, few visible‐light‐transparent, electrically conductive substrate materials can survive such conditions.…”