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Will man mimick nature to power the hydrogen economy?

Artificial photosynthesis and solar cells are just one of the exciting projects that Mallouk's teams are working on.  (Source: Penn State University)
A new research study has created a synthetic photosynthetic complex which has a net efficiency of 0.3 percent

Photosynthesis is the fundamental energy capture process which forms the foundation of all life on Earth.  On a most basic level, it involves using sunlight to split water molecules into hydrogen and oxygen and then using the hydrogen captured to fuel sugar production.   With hydrogen becoming more popular as a possible alternative fuel source, many researchers have yearned to duplicate this most basic of natural processes to allow for cheap, efficient hydrogen production.  They had little success -- until now.

In the past, natural and synthetic dye molecules which tried to split hydrogen and water were consumed during the reactions and did not provide a sustained reaction.  Worse yet, the chemical reactions were often from a net perspective endothermic; in other words they required energy instead of producing it.  Part of this is because of the ease with which oxygen and hydrogen recombine, and the fact that most of these investigated catalysts also catalyze the recombination, destroying your products.

Thomas Mallouk, a DuPont Professor of Materials Chemistry and Physics, and W. Justin Youngblood, postdoctoral fellow in chemistry, together with collaborators at Arizona State University succeeded where others have failed. The researchers developed a dye/catalyst system that mimics the oxidative and electron transfer processes of photosynthesis, ultimately producing hydrogen gas.  Their findings were presented at the meeting of the American Association for the Advancement of Science today in Boston.

Clusters of molecules using iridium oxide molecules as a center catalyst, surrounded by light absorbing orange-red dye molecules comprise the finished product.  The 2 nm complexes are roughly half dye and half catalyst in terms of diameter.  Orange-red dye was selected due to its extensive experimental record and its ability to absorb high energy blue wavelength light.

Water molecules bond to the complex, and when the complex absorbs sunlight, it splits them into hydrogen and oxygen.  Mallouk enthuses upon its near biological efficiency, stating, "Each surface iridium atom can cycle through the water oxidation reaction about 50 times per second.  That is about three orders of magnitude faster than the next best synthetic catalysts, and comparable to the turnover rate of Photosystem II in green plant photosynthesis."

The process needs a tiny bit of juice to get started.  The voltage required to split water is 1.23 V, and the system is almost at this power level.  By adding 0.3 V from titanium dioxide anode and platinum cathode electrodes, the water begins to split.  Separating the electrodes effectively reduces hydrogen/oxygen recombination.

The current process has a positive efficiency of about 0.3 percent.  This sounds pretty measly, but as Mallouk puts it, "Nature is only 1 to 3 percent efficient with photosynthesis.  Which is why you cannot expect the clippings from your lawn to power your house and your car. We would like not to have to use all the land area that is used for agriculture to get the energy we need from solar cells."

Mallouk hopes to eventually achieve efficiencies better than that of natural processes.  By changing the molecular geometry, he plans on upping the efficiency by better allowing light to be absorbed or by improving the bonding of water molecules to the surface of the complex.

Mallouk states optimistically, "This is a proof-of-concept system that is very inefficient. But ultimately, catalytic systems with 10 to 15 percent solar conversion efficiency might be achievable.  If this could be realized, water photolysis would provide a clean source of hydrogen fuel from water and sunlight."

The fact that the efficiency is anywhere near that of the Photosystem II protein complex, a marvel of biological design, is impressive in itself.  The fact that this system could be competitive one day with modern solar technology (currently around 10 percent efficient) and help to replace fossil fuels is even more impressive. 

With hydrogen fuel looking more and more promising, Mallouk and Youngblood's research is certainly a significant breakthrough. 



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RE: Reminds me of...
By JonnyDough on 2/19/2008 12:30:50 AM , Rating: 1
I'd just like to say that I believe there are forces on earth we're unaware of that can provide more power than solar energy. Still, solar energy seems to me to be the most viable, free source we have. It's everlasting (at least until the sun burns out, and then...well there are other suns). Once we understand more about dark matter and so on, I believe we'll find our renewable resource. The idea of a crystal that can output a significant amount of energy over a long time is not that far fetched. We have no idea really what lies beyond our own galax, and for that matter, within it. This kind of news is exciting to me everytime I hear about advances in solar power, especially those that could possibly be commercialized. My hat is off to anyone who can get rid of our coal dependency. It is a horrible way to power our world.


RE: Reminds me of...
By Schrag4 on 2/19/2008 11:17:06 AM , Rating: 2
"(at least until the sun burns out, and then...well there are other suns)"

Yeah, then we just go to the next solar system, beam down to the first planet we find, and breathe the oxygen-rich, toxin-less air, walk upright in the earth-like gravity, and talk to the english-speaking alien race that lives there. I saw it on Star Trek, it must not be that hard!

In all seriousness, I suppose by the time our sun goes out, we may have advanced our technology (and our genetics??) enough to adapt to other solar systems and their planets, or maybe adapt them to us (terraforming). Of course none of us or our great-great granchildren will see any of this. If you think we'll have these types of technologies sooner, then you're like the crowd from 50 years ago who thought we'd have flying cars by the year 2000.

Cool article though. I, too, get a little excited inside when I hear about these new energy advancements.


RE: Reminds me of...
By JonnyDough on 2/19/2008 2:26:17 PM , Rating: 1
"I saw it on Star Trek, it must not be that hard!"

Heh, my post was a bit of sarcasm. By the time the sun burns out the human race will likely be extinct due to something else. Collision with an asteroid, global temperature change, a disease. We're not likely to ever hear on the news that our sun just ran out of hydrogen. =)


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