Simple, Cost-Effective Solution for Splitting Water into Hydrogen and Oxygen

Scientists have been studying particulate photocatalysts as an easy and economical solution to split water into oxygen and hydrogen for the large-scale production of hydrogen through the use of solar energy.

Developing a photocatalyst that can efficiently make use of visible light, which forms a huge part of solar energy, in the water decomposition reaction is crucial.

Barium tantalum oxynitride (BaTaO₂N), an oxynitride semiconductor material, absorbs visible light with a wavelength ranging up to 650 nm and consists of a band structure that has the ability to decompose water into oxygen and hydrogen.

So far, loading of BaTaO₂N granules with co-catalyst fine particles has not been possible. The fine particles are the reaction active sites that exhibit high dispersion and good adhesion.

As part of this study, carried out under the guidance of the Research Initiative for Supra-Materials of Shinshu University, the co-catalyst fine particles were discovered to be highly dispersed on the surface of the single crystal fine particles of BaTaO₂N produced by the flux technique when the photodeposition method and the impregnation-reduction method were employed consecutively.

Thus, the efficiency of the hydrogenation reaction with the BaTaO₂N photocatalyst was enhanced by almost 100 times when compared to the traditional one.

There has also been an improvement in the efficiency of the two-step excitation type (Z-scheme type) water decomposition reaction together with the oxygen generation photocatalyst.

Using transient absorption spectroscopy, it was shown that there were fewer chances that the Pt-assisted catalyst microparticles promoted by the new technique will cause recombination of electrons and holes since they withdraw electrons from the BaTaO₂N photocatalyst in an efficient manner.

The reduction reaction on the photocatalyst can be supported without the agglutination of Pt fine particles by supporting a small portion of Pt co-catalyst by the impregnation-reduction technique in advance.

Consequently, Pt co-catalyst fine particles are uniformly promoted by photodeposition on BaTaO₂N particles. Thus, it is regarded that producing electricity by Pt co-catalyst fine granules advanced efficiently.

It was verified that the use of BaTaO₂N, produced using a suitable flux and with a low density of defects, is also essential for promoting a highly dispersed Pt co-catalyst. This study drastically improved the activity of the BaTaO₂N photocatalyst and elucidated its mechanism.

It is predicted that the findings of this study will pave the way for long-wavelength-responsive photocatalysts that activate the water decomposition reaction with high efficiency.

This study was carried out in collaboration with the Japan Technological Research Association of Artificial Photosynthetic Chemical Process (ARPChem) and forms part of the “Artificial Photosynthesis Project” of the New Energy and Industrial Technology Development Organization (NEDO).

Journal Reference:

Wang, Z., et al. (2021) Sequential cocatalyst decoration on BaTaO₂N towards highly-active Z-scheme water splitting. Nature Communications. doi.org/10.1038/s41467-021-21284-3.