Solar Hydrogen Research

energy conversion

Sequential cocatalyst decoration on BaTaO2 N towards highly-active Z-Scheme water splitting- Shinshu University

In order to enable large-scale hydrogen production using solar energy, particulate photocatalysts are being researched as a simple and cost-effective solution to splitting water into hydrogen and oxygen. It is necessary to develop a photocatalyst that can efficiently use visible light, which accounts for a large part of solar energy, in the water decomposition reaction. Barium tantalum oxynitride (BaTaO₂N) is an oxynitride semiconductor material that absorbs visible light up to 650 nm and has a band structure capable of decomposing water into hydrogen and oxygen. Until very recently, it had not been possible to load BaTaO₂N granules with co-catalyst fine particles, which are reaction active sites, with good adhesion and high dispersion.

In this study led by the Research Initiative for Supra-Materials of Shinshu University, the co-catalyst fine particles were found to be highly dispersed on the surface of the single crystal fine particles of BaTaO₂N synthesized by the flux method when the impregnation-reduction method and the photodeposition method were sequentially applied.

As a result, the efficiency of the hydrogenation reaction using the BaTaO₂N photocatalyst has been improved to nearly 100 times that of the conventional one, and the efficiency of the two-step excitation type (Z scheme type) water decomposition reaction in combination with the oxygen generation photocatalyst has also been improved. Transient absorption spectroscopy reveals that the Pt-assisted catalyst microparticles supported by the new method are less likely to induce recombination of electrons and holes because they efficiently extract electrons from the BaTaO₂N photocatalyst.

By supporting a small amount of Pt co-catalyst by the impregnation-reduction method in advance, the reduction reaction on the photocatalyst is promoted without agglutination of Pt fine particles. As a result, Pt cocatalyst fine particles are evenly supported by photodeposition on BaTaO₂N particles. The resultant extraction of electricity by Pt co-catalyst fine granules is considered to have proceeded efficiently.

Schematic of sequential Pt-cocatalyst deposition on BaTaO2N. Credit: Cited from Wang, Z., Luo, Y., Hisatomi, T. et al. Sequential cocatalyst decoration on BaTaO2N towards highly-active Z-scheme water splitting. Nat Commun 12, 1005 (2021). Copyright © 2021, The Authors.

It was also confirmed that the use of BaTaO₂N, which is synthesized using an appropriate flux and has a low density of defects, is also important for supporting a highly dispersed Pt co-catalyst. This study dramatically improved the activity of the BaTaO₂N photocatalyst and clarified its mechanism. The results of this research are expected to lead to the development of long-wavelength-responsive photocatalysts that drive the water decomposition reaction with high efficiency.

Pt-modified BaTaO2N photocatalysts. Credit: Cited from Wang, Z., Luo, Y., Hisatomi, T. et al. Sequential cocatalyst decoration on BaTaO2N towards highly-active Z-scheme water splitting. Nat Commun 12, 1005 (2021). Copyright © 2021, The Authors.

Further research has been is being done in Belgium to support the above research

KU Leuven team creates solar panel that produces hydrogen from moisture in air

08 March 2019

Bioscience engineers at KU Leuven have created a solar panel that produces hydrogen gas from moisture in the air. After ten years of development, the panel can now produce 250 liters per day—a world record, according to the researchers. Twenty of these solar panels could provide electricity and heat for one family for an entire winter.

A traditional solar panel converts between 18 to 20% of the solar energy into electricity. If that electric power is used to split the water into hydrogen gas and oxygen, you lose a lot of energy. The KU Leuven bioscience engineers solved this problem by designing a solar panel of 1.6 m² that converts 15% of the sunlight straight into hydrogen gas.

It’s a unique combination of physics and chemistry. In the beginning, the efficiency was only 0.1 per cent, and barely any hydrogen molecules were formed. Today, you see them rising to the surface in bubbles. So that’s ten years of work—always making improvements, detecting problems. That’s how you get results.—Professor Johan Martens

Twenty of these panels produce enough heat and electricity to get through the winter in a thoroughly insulated house and still have power left. Add another twenty panels, and you can drive an electric car for an entire year.—KU Leuven researcher Jan Rongé

Today, most hydrogen gas is produced using oil and gas.—Grey hydrogen gas, in other words—not a big win for the climate or the environment. The KU Leuven researchers believe this is about to change.

The solar panel will be under test in Oud-Heverlee, a rural town in Flemish Brabant. The house we visit is well insulated and gets most of its power from solar panels, a solar boiler, and a heat pump. It is not connected to the gas grid. It only uses power from the grid in the winter.

Soon, 20 hydrogen gas panels will be added to this mix. If all goes well, more panels will be installed on a piece of land in the street. This will allow the other 39 families in the street to benefit from the project as well. The hydrogen gas produced in the summer will be stored and converted into electricity and heat in the winter.

The hydrogen gas produced in the summer can be stored in an underground pressure vessel until winter. One family would need about 4 cubic meters of storage—the size of a regular oil tank.

For Johan Martens, a test project like the one in Oud-Heverlee is what he and his team have been working towards for years.

We wanted to design something sustainable that is affordable and can be used practically anywhere. We’re using cheap raw materials and don’t need precious metals or other expensive components.—Johan Martens