barium tantalum oxynitride
Fabrication of BaTaO2N Thin Films by Interfacial Reactions of ...
Thin films of barium tantalum oxynitride (BaTaO2N) with thicknesses of 150–680 nm are grown on TaN/Ta substrates via the interfacial reaction ...
Formation of barium-tantalum oxynitrides
Oxynitride powders are suitable for sintering to form dielectric ABO3-type perovskites have been prepared by nitriding barium carbonate and tantalum oxide.
Both heat treatment in air and reaction in flowing ammonia yield isostructural oxynitride phases, but the amount and electronic state of the oxynitrides depend on the nitriding gas conditions.
A red-brown oxynitride of high nitrogen content is described as Ba2Ta2O3N2 containing Ta (IV) ions but after heat treatment in the air the color changes to white indicative of Ta(V) and stoichiometry of BaTaO2N results.
A third possibility is identified in an oxynitride containing both Ta (IV) and Ta (V) with intermediate nitrogen content.
Through studies involving the thermal analysis and X-ray diffraction, the materials are characterized in powder form and possible sintering conditions are suggested which involve a rapid heating rate and a densification temperature of 1500 °C.
Oxynitrogenography: Controlled Synthesis of Single-Phase
tantalum nitride (Ta3N5) and tantalum oxynitride (β-TaON) phosphate-modified barium-doped tantalum.
Synthesis of BaTaO 2 N oxynitride from Ba-rich oxide
Barium tantalum oxynitride (BaTaO2N) with an absorption edge of ca. 660 nm is one of the most promising photocatalysts for solar water splitting.
Synthesis of BaTaO2N oxynitride from Ba-rich oxide
Barium tantalum oxynitride (BaTaO2N) with an absorption edge of ca.
660 nm is one of the most promising photocatalysts for solar water splitting and is usually synthesized by nitriding a mixture of Ba and Ta-containing compounds with a Ba/Ta molar ratio of unity under ammonia flow at high temperature, usually causing a high density of defect sites.
Herein, we introduce a novel synthesis method for BaTaO2N (BTON) by employing Ba-rich LiBa4Ta3O12, prepared by a flux method, as a precursor of nitridation.
As a comparison, BaTaOx was prepared by a conventional solid-state reaction and used as the precursor.
The as-nitrided samples were correspondingly denoted as BTON-Flux and BTON-SSR.
It was found that well-crystallized BTON oxynitride can be similarly obtained by both methods, but the BTON-Flux sample exhibits significantly decreased defect density and enhanced surface area relative to the BTON-SSR sample.
As a result of their structural differences, the photocatalytic water splitting performance of the BTON-Flux sample, regardless of the H2-evolving half-reaction in the presence of methanol or Z-scheme overall water splitting, is much better than that of BTON-SSR.
This study may open up a novel strategy for preparing oxynitride photocatalyst with decreased defect density for the promotion of solar water splitting.
Previously, we applied the flux growth method to synthesize La 1−x Sr x Fe 1−y Ti y O 3, CdTiO 3, Cd 2 Nb 2 O 7, Cd 2 Ta 2 O 7 (Hojamberdiev et al., 2016a), Ba 5 Nb 4−x Ta x O 15, ZnIn2S4, LaTaON 2, PrTaON 2, BaNb 0.5 Ta 0.5 O 2 N (Kawashima et al., 2018a), and N-doped ZnTiO 3 (Wagata et al., 2019) crystals with less defect density, increased surface area, improved particle dispersion and/or high crystallinity.
synthesized BaTaO 2 N by employing Ba-rich LiBa 4 Ta 3 O 12 prepared by a flux method and exhibited much higher hydrogen evolution activity both in half-reaction and in Z-scheme overall water splitting due to the decreased defect density and surface area enhancement.
Previously, we explored the effects of various fluxes (KCl, KI, KF, MgCl 2, CaCl 2, SrCl 2, BaCl 2, K 2 SO 4, K 2 MoO 4, and K 2 CO 3 ), holding temperature (700-950 • C), reaction time (0-10 h), and solute concentration (1-50 mol %) on the formation of BaTaO 2 N crystals using BaCO 3 and Ta 2 O 5 under NH 3 flow.
Tantalum (Oxy)Nitride: Narrow Bandgap Photocatalysts for.
investigated the bandgap positions of tantalum oxynitride perovskite ... with barium (Ba) to promote the photocatalytic H2 evolution rate.
Photocatalytic water splitting, which directly converts solar energy into hydrogen, is one of the most desirable solar-energy-conversion approaches.
The ultimate target of photocatalysis is to explore efficient and stable photocatalysts for solar water splitting.
Tantalum (oxy)nitride-based materials are a class of the most promising photocatalysts for solar water splitting because of their narrow bandgaps and sufficient band energy potentials for water splitting.
Tantalum (oxy)nitride-based photocatalysts have experienced intensive exploration, and encouraging progress has been achieved over the past years.
However, the solar-to-hydrogen (STH) conversion efficiency is still very far from its theoretical value.
The question of how to better design these materials in order to further improve their water-splitting capability is of interest and importance.
This review summarizes the development of tantalum (oxy)nitride-based photocatalysts for solar water splitting.
Special interest is paid to important strategies for improving photocatalytic water-splitting efficiency.
This paper also proposes future trends to explore in the research area of tantalum-based narrow bandgap photocatalysts for solar water splitting.
The effect of downstream laser fragmentation on the specific surface area and photoelectrochemical performance of barium tantalum oxynitride
Laser fragmentation is a new method for increasing the surface area of oxynitrides.
•Laser fragmentation of BaTaO2N particles results in the loss of their N content.
•The fragmented oxynitride particles show lower crystalline quality.
•The fragmented oxynitride photoanodes show lower photoelectrochemical activity.
•An amorphous layer is formed after seven fragmentation passages.
One approach to improve the photoelectrochemical solar water splitting performance of photoanodes based on oxynitride perovskite particles is through increasing the active surface area which allows the generation of more electron-hole pairs that contribute in the water reduction and oxidation reactions.
In this study, we explore the pros and cons of downstream laser fragmentation as a method to increase the specific surface area of oxynitride particles and highlight the important issues that must be considered for effective solar water splitting.
The synthesis of particles with a high surface area of up to 32.4 m2 g−1 is demonstrated.
Furthermore, the fragmented oxynitrides revealed lower absorbance values, a blue shift in the absorption edge, and a higher background absorbance.
These observations, in addition to the lower crystalline quality of the fragmented oxynitrides, were attributed to the loss of N content during fragmentation and the formation of secondary phases.
The photoanodes based on the fragmented particles showed lower photocurrents than those prepared from the un-fragmented particles even though the surface area was increased.
The decrease in photoactivity was ascribed to the presence of more grain boundaries in the fragmented oxynitride photoanodes which leads to more recombinations of the photogenerated carriers.
Interestingly, after seven fragmentation passages, the photocurrent starts to increase again due to the formation of an amorphous layer which improves the transport of the photogenerated carriers.
Laser fragmentation in the liquid is a novel method for the increased surface area of oxynitride particles and enhanced water splitting photoactivity.
Cobalt phosphate-modified barium-doped tantalum nitride.
Spurred by the decreased availability of fossil fuels and global warming, the idea of converting solar energy into clean fuels has been widely recognized.
Hydrogen produced by photoelectrochemical water splitting using sunlight could provide a carbon dioxide lean fuel as an alternative to fossil fuels.
A major challenge in photoelectrochemical water splitting is to develop an efficient photoanode that can stably oxidize water into oxygen.
Here we report an efficient and stable photoanode that couples an active barium-doped tantalum nitride nanostructure with a stable cobalt phosphate co-catalyst.
The effect of barium doping on the photoelectrochemical activity of the photoanode is investigated.
The photoanode yields a maximum solar energy conversion efficiency of 1.5%, which is more than three times higher than that of state-of-the-art single-photon photoanodes.
Further, stoichiometric oxygen and hydrogen are stably produced on the photoanode and the counter electrode with Faraday efficiency of almost unity for 100 min.
The globally ongoing solar fuel projects reflect the pressing need for producing fuels from sunlight so that solar energy can be stored and used whenever and wherever it is needed 1, 2, 3.
Photoelectrochemical (PEC) splitting of water into hydrogen and oxygen is a promising way to directly convert solar energy into fuel 4, 5, 6, 7.
Among the proposed configurations for PEC cells 6, the dual band gap PEC cell constructed by electrically connecting an n-type photoanode and a p-type photocathode in series is the most economical one that has the potential to realize the 10% solar-to-fuel conversion efficiency required for practical application.
Constructing such a PEC cell requires both a photoanode and photocathode with high activity for water oxidation and reduction.
Although many highly active and stable p-type photocathodes have been developed in recent years 8, 9, 10, 11, 12, the more challenging task is to develop a photoanode that can stably oxidize water into oxygen under sunlight with high efficiency.
The poor stability because of the strong oxidizing conditions and the low efficiency because of the high overpotential of four-electron water oxidation are the major challenges in designing the photoanode.
To the best of our knowledge, the solar energy conversion efficiency of single-photon photoanodes reported so far are below 0.5% at best 13, 14, 15, 16, 17.
Thus, there is still much room for improvement in the activity of the photoanode to achieve high efficiency in an integrated dual band gap PEC cell.
A PEC cell is a complex system, every aspect of which should be optimized to maximize device performance.
For the photoanode part, the structure, material properties, and co-catalyst modification are the three determining factors of its efficiency.
The use of nanostructures is an effective way to improve the efficiency of the photoanode as it results in enhanced carrier collection, improved light absorption, and surface area-enhanced charge transfer 18.
Choosing a visible-light-responsive semiconductor with energy band positions that favor water oxidation and reduction is also effective in improving the efficiency of the photoanode.
The semiconductor material properties can be further improved by doping with appropriate impurities, a technique that is indispensable in the semiconductor industry.
Modification of the photoanode with a suitable oxygen evolution co-catalyst is equally important as it improves efficiency by lowering the overpotential and preventing photo corrosion.
Recently, we reported a highly efficient photoanode made of a vertically aligned tantalum nitride (Ta3N5) nanorod array modified with an iridium oxide co-catalyst 15.
The photoanode, owing to its nanorod structure and Ta3N5 material properties, exhibited state-of-the-art efficiency at the time of reporting.
Yet, the solar energy conversion efficiency of this photoanode was still below 0.5%.
Unintentionally doped Ta3N5 is an n-type semiconductor with a bandgap of 2.1 eV, capable of absorbing a large portion of the solar radiation, up to a wavelength of ~590 nm.
The energy bands of Ta3N5 straddle the water redox potentials 19, which is energetically more suitable for water splitting than most visible-light-responsive oxides (for example, Fe2O3 (ref.
14 ), WO3 (ref.
20 ) and BiVO4 (ref.
21 )), having a conduction band too positive for H2 evolution.
Ta3N5 has been widely used for both photocatalytic and PEC water splitting 22, 23, 24, 25, 26, 27, 28.
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