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TiSi2 Semiconductor for Photocatalytic Splitting of Water and Subsequent Gas Storage

Researchers at the Max Planck Institute for Bioinorganic Chemistry have developed a titanium disilicide (TiSi2) semiconductor photocatalyst that splits water into hydrogen and oxygen. The semiconductor also stores the gases produced, enabling the simple separation of hydrogen and oxygen.

Lead researcher Martin Demuth and his team report on their work in the current issue of Angewandte Chemie International Edition.

The generation of hydrogen and oxygen from water by means of semiconductors is an important contribution to the use of solar energy. Semiconductors suitable for use as photocatalysts have been difficult to obtain, have unfavorable light-absorption characteristics, or decompose during the reaction.

—Martin Demuth

Demuth and his team proposed a class of semiconductors that have not been used for this purpose before: silicides. For a semiconductor, titanium disilicide has very unusual optoelectronic properties that are ideal for use in solar technology. In addition, this material absorbs light over a wide range of the solar spectrum, is easily obtained, and is inexpensive.

At the start of the reaction, a slight formation of oxide on the titanium disilicide results in the formation of the requisite catalytically active centers.

Another aspect of this system is the simultaneous reversible storage of hydrogen. The storage capacity of titanium disilicide is smaller than the usual storage materials, but it is technically simpler. Significantly lower temperatures are sufficient to release the stored hydrogen. The oxygen is stored as well, but is released under different conditions than the hydrogen, requiring temperatures of more than 100°C and darkness.

Demuth and his German, American, and Norwegian partners have founded a company in Lörrach, Germany, for the further development and marketing of the proprietary processes.

Resources:

  • Peter Ritterskamp, Andriy Kuklya, Marc-André Wüstkamp, Klaus Kerpen, Claudia Weidenthaler, Martin Demuth. “A Titanium Disilicide Derived Semiconducting Catalyst for Water Splitting under Solar Radiation - Reversible Storage of Oxygen and Hydrogen”, Angew. Chem., Int. Ed., 2007 46 (41) 7770–7774 doi: 10.1002/anie.200701626

Comments

Rafael Seidl

Very interesting ... especially the ability to desorb the hydrogen and oxygen separately, permitting them to be stored separately until needed to run a fuel cell.

However, there are a lot of question to ask here:

(a) how expensive is TiSi2 to produce?
(b) what are its mechanical properties?
(c) what is the energy conversion efficiency for regular sunlight at perpendicular incidence?
(d) does the water film have to be between the semiconductor and a pane of glass, or can it be in the semiconductor's shadow?
(e) is the heat fron strong sunlight sufficient for hydrogen desorption?
(f) how specific are the desorption processes?

Without any of this info, how can anyone know if this will ever make he leap from scientific curiosity to commercially relevant technology?

GreenPlease

To me, the promising aspect of this technology is the ability to separately desorb the oxygen. I have often wondered what the efficiency/power density gain in a PEM fuel cell if the cathode were exposed to pure oxygen.

I don't see any provisions for a transport mechanism. Perhaps you could have a central fuel cell surrounded by glass enclosed TiSi2 field. Assuming that one could desorb the H2 in real time, perhaps the void between the glass and the TiSi2 would be sufficient to transport the H2. O2 could be desorbed at night and stored for use during the day.

Jim G.

it says right in this article that TiS2 is "easily obtained, and is inexpensive". I'm sure the paper itself has tables with conversion efficiency vis a vis some form of sunlight. It sounds practical and sensible to me compared to a lot of other research.

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