Water Photolysis: Turning the Sun's Light Directly into Hydrogen

The concept of the "hydrogen economy" was quite popular until people started to ask where all that hydrogen would come from. One possible path is using bacteria, another is solar energy: Penn State researchers have announced a proof-of-concept device that can split water and produce recoverable hydrogen. So far, it's quite inefficient. "But ultimately, catalytic systems with 10 to 15 percent solar conversion efficiency might be achievable," said Thomas E. Mallouk, Professor of Materials Chemistry and Physics. "If this could be realized, water photolysis would provide a clean source of hydrogen fuel from water and sunlight."

The catalyst system, combined with a dye, can mimic the electron transfer and water oxidation processes that occur in plants during photosynthesis, but if 10 to 15% efficiency could be achieved, this would be much higher than what nature can do.

The key to their process is a tiny complex of molecules with a center catalyst of iridium oxide molecules surrounded by orange-red dye molecules. These clusters are about 2 nanometers in diameter with the catalyst and dye components approximately the same size. [...]

"Each surface iridium atom can cycle through the water oxidation reaction about 50 times per second," said Mallouk. "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." Photosystem II is the protein complex in plants that oxidizes water and starts the photosynthetic process. [...]

Their current system achieves an efficiency of about 0.3 percent.

"Nature is only 1 to 3 percent efficient with photosynthesis," said Mallouk, "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."

The researchers say that they have many ways to improve the system and make it more efficient.

There's no silver bullet, and while it's important to keep developing batteries and hyper-capacitors to store electricity, it's good that other paths are being explored at the same time, even if they turn out to be impractical for a while. You never know where a big breakthrough will come from. Lets not put all our eggs in the same basket.

::Solar cell directly splits water for hydrogen

See also: ::Hairy Solar Panels Could Result From Nanowire Breakthrough, ::CoolEarth Raises $21 Million for Solar Balloons, ::A2: The Hydrogen-Powered Hypersonic Airliner, ::E. Coli: The Next Big Source of Hydrogen Fuel?

Tags: Energy | Technology

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