New Energy and Industrial Technology Development Organization (NEDO) and the Japan Technological Research Association of Artificial Photosynthetic Chemical Process (ARPChem) announced Sept 4, 2018, that they have developed a tantalum nitride photocatalyst capable of decomposing water in the visible light region in cooperation with the University of Tokyo and Shinshu University.
Since about 2000, tantalum nitride has been considered as a promising next-generation photocatalyst material. However, it was difficult to synthesize high-quality nitride particulates. And this is the first time in the world that a tantalum nitride photocatalyst has actually been produced and the decomposition of water has been confirmed, according to NEDO and ARPChem.
The intensity of sunlight peaks mainly in the visible light region (400-800nm). So, with a photocatalyst that absorbs light in this region and decomposes water, it becomes possible to efficiently utilize solar energy. However, many conventional photocatalysts mainly absorb light in the ultraviolet region (400nm or less), and it has been necessary to make a photocatalyst that absorbs longer-wavelength light.
This time, NEDO and ARPChem succeeded in developing a monocrystalline tantalum nitride (Ta3N5) particulate photocatalyst that absorbs visible light and decomposes water. By dispersing the photocatalyst in water, it is possible to absorb visible light with a waveband of 400-600nm and decompose water.
Also, when the photocatalyst is fixed on a substrate, it can be embedded in a photocatalyst panel reactor. Because the intensity of sunlight becomes strongest at a wavelength of about 600nm, solar energy is expected to be efficiently used.
By nitriding composite oxide particulates (potassium tantalate, KTaO3) in a shorter time (less than 1/10), monocrystalline tantalum nitride particulates are directly formed on the composite oxide particulates, and a co-catalyst that facilitates hydrogen-generating reaction is attached. As a result, it becomes possible to effectively use (1) photoexcited electrons whose nitride particulates were improved in quality and (2) positive holes for water-splitting reaction.