Splitting Water with Sunlight

[OKIsItJustMe]

http://www.physorg.com/news109941196.html

Splitting Water with Sunlight

Hydrogen is one of the most important fuels of the future, and the sun will be one of our most important sources of energy. Why not combine the two to produce hydrogen directly from solar energy without any detours involving electrical current? Why not use a process similar to the photosynthesis used by plants to convert sunlight directly into chemical energy?

Researchers from the German Max Planck Institute have now developed a catalyst that may do just that. As they report in the journal Angewandte Chemie, titanium disilicide splits water into hydrogen and oxygen. And the semiconductor doesn’t just act as a photocatalyst, it also stores the gases produced, which allows an elegant separation of hydrogen and oxygen.

“The generation of hydrogen and oxygen from water by means of semiconductors is an important contribution to the use of solar energy,” explains Martin Demuth (of the Max Planck Institute for Bioinorganic Chemistry in Mülheim an der Ruhr). “Semiconductors suitable for use as photocatalysts have been difficult to obtain, have unfavorable light-absorption characteristics, or decompose during the reaction.”

Demuth and his team have now proposed a class of semiconductors that have not been used for this purpose before: Silicides. For a semiconductor, titanium disilicide (TiSi2) 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. “Our catalyst splits water with a higher efficiency than most of the other semiconductor systems that also operate using visible light,” says Demuth.

One aspect of this system that is particularly interesting 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. Most importantly, 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. It requires temperatures over 100°C and darkness. “This gives us an elegant method for the easy and clean separation of the gases,” explains Demuth. He and his German, American, and Norwegian partners have founded a company in Lörrach, Germany, for the further development and marketing of the proprietary processes.

The paper, A Titanium Disilicide Derived Semiconducting Catalyst for Water—Splitting under Solar Radiation—Reversible Storage of Oxygen and Hydrogen, can be found here:
http://dx.doi.org/10.1002/anie.200701626

[mike_c]

1. this is very interesting....

I wonder what sort of efficiency is possible?

[eppur_se_muova]

2. This is a REALLY big breakthrough.

It may not turn out to use this *particular* system on an industrial scale. But now that the trick is known, other examples are likely to come to light. Think of the rapid progress that was made with copper oxide-based superconductors after they were first discovered -- this could compare with that, and is something that chemists have been searching for for the last few decades, at least.

For those who don't know, Angewandte Chemie is a refereed publication of the "Society of German Chemists" (Gesellschaft Deutscher Chemiker) and is one of the most respected publications in chemistry. It specializes in short communications and is the preferred journal of "late breaking news" for many German/European chemists.

(So this is not some retired dentist who invented this in his bathtub, or some snake oil salesman promising FREE UNLIMITED ENERGY FROM WATER!!)

[DramaOnHwy61]

8. Hey I happen to be a retired dentist...

...and I enjoy inventing in my bathtub for hours
;-)

[eppur_se_muova]

10. Nothing wrong with retired dentists, as long as they obey the laws of thermodynamics! nt

[pnutbutr]

3. McMaster

Very cool stuff.

A guy named McMaster spent decades developing a hydrogen powered engine in his home garage using solar panels to run current through water to produce his own hydrogen fuel for testing it. Incredibly cool engine design. Check it out. http://www.mcmastermotor.com/concept.htm

[phantom power]

4. I would quibble with his claim that H2 is safe to handle....

On the other hand, I also don't see why his basic design couldn't be used with other fuels. It might require some additional machinery, but the main advantages of the design remain unchanged, regardless of what kind of fuel is being burned.

[OKIsItJustMe]

5. H2 is relatively safe

As compared (for example) to gasoline, which many of us treat as innocuous.

Gasoline and gasoline vapors will travel surprising distances along the floor or ground if leaked. H₂ will rise and spread along a ceiling if leaked indoors. If leaked outdoors, it tends to rise harmlessly. (Even if ignited.)

[phantom power]

6. On the other hand, I don't have to store gasoline in my tank at 5000psi...

and none of my gasoline infrastructure needs to be absolutely air-tight.

[OKIsItJustMe]

7. Hydrogen safety

http://www.eere.energy.gov/hydrogenandfuelcells/pdfs/h2_safety_fsheet.pdf

[DramaOnHwy61]

9. Nice idea, but I bet there's a huge lubrication problem...

...between the wobbling disk and the inner cylinder wall.
The Wankel engine motored into oblivion for much less.
(ok, off-topic).

[pnutbutr]

11. little lubrication

It actually requires very little lubrication apparently only for the two locations where the drive shaft enters the combustion chamber. Speaking of the Wankel, it is ideal for hydrogen since it has no valves which are the weak point for the standard combustion engine design running on hydrogen.