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Photosynthesis Redirected To Produce Hydrogen As Fuel

Hydrogen holds great promise as the "green" energy source of the future. Though ubiquitous, it rarely exists in a pure form in nature. Present methods of producing hydrogen for fuel -- such as extraction from natural gas -- are energy inefficient and polluting.

Hydrogen's potential as a "clean" fuel cannot be fully realized until it can be generated from renewable resources.

In an article published in the June 2001 issue of Photochemistry and Photobiology, researchers from the University of Tennessee's Center for Environmental Biotechnology (CEB) and the Oak Ridge National Laboratory (ORNL) demonstrate that photosynthesis -- the process that plants use to make food from sunlight -- can be redirected to produce hydrogen.

The team of CEB researchers -- including undergraduate student Jennifer Millsaps, UT/ORNL professor Elias Greenbaum and UT professor Barry Bruce (biochemistry, cellular and molecular biology) -- extracted intact photosynthetic complexes (Photosystem I) from spinach plants and coated one side of each isolated complex with platinum atoms.

In the presence of an added electron donor, this "platinized complex" was able to use visible light to produce hydrogen.

Photosynthesis results from the cooperation of two photosystems called Photosystem I (PSI) and Photosystem II (PSII) that are coupled together in the plant's chloroplast by an intermediary complex.

The green plant normally reduces carbon dioxide to carbohydrates in PSI in a complex set of enzymatic reactions powered by the electrons produced when water is split in PSII.

The UT/ORNL experiments uncoupled PSI from PSII, removing PSII and the intervening complex and redirecting PSI reactions to produce molecular hydrogen.

This is the first time platinized PSI has been used to generate hydrogen, and represents the smallest nanoscale hydrogen-evolving system ever created.

So far, diversion to hydrogen production must be supported by feeding PSI a high-energy donor such as ascorbate. The next step is to extract PSI and PSII separately, and then join them back together head to toe, allowing PSII to directly supply PSI with electrons derived from splitting water.

If done successfully, this nanoscale photosystem could produce a constant supply of hydrogen and oxygen, a fuel that when burned produces heat -- leaving only water as the waste product.

Jennifer Millsaps, the undergraduate student from Maryville College who acted as lead author on the article, was supported by the Professional Internship Program (PIP) of the Oak Ridge Institute of Science and Education (ORISE). The research was supported by the U.S. Department of Energy.

Related website:

UT Center for Environmental Biotechnology

[Contact: Dr. Elias Greenbaum, Dr. Barry Bruce]






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