A team of four chemists at the University of Rochester
have begun work on a new kind of system to derive usable hydrogen fuel from
water using only sunlight.
The project has caught the attention of the U.S. Department
of Energy, which has just given the team nearly $1.7 million to pursue the
design.
"Everybody talks about using hydrogen as a super-green
fuel, but actually generating that fuel without using some other non-green
energy in the process is not easy," says Kara Bren, professor in the Department
of Chemistry. "People have used sunlight to derive hydrogen from water
before, but the trick is making the whole process efficient enough to be
useful."
Bren and the rest of the Rochester team—Professor of Chemistry Richard
Eisenberg, and Associate Professors of Chemistry Todd Krauss, and Patrick
Holland—will be investigating artificial photosynthesis, which uses sunlight to
carry out chemical processes much as plants do. What makes the Rochester
approach different from past attempts to use sunlight to produce hydrogen from
water, however, is that the device they are preparing is divided into three
"modules" that allow each stage of the process to be manipulated and
optimized far more easily than other methods.
The first module uses visible light to create free
electrons. A complex natural molecule called a chromophore that plants use to
absorb sunlight will be re-engineered to efficiently generate reducing
electrons.
The second module will be a membrane suffused with carbon
nanotubes to act as molecular wires so small that they are only one-millionth
the thickness of a human hair. To prevent the chromophores from re-absorbing
the electrons, the nanotube membrane channels the electrons away from the
chromophores and toward the third module.
In the third module, catalysts put the electrons to work
forming hydrogen from water. The hydrogen can then be used in fuel cells in
cars, homes, or power plants of the future.
By separating the first and third modules with the nanotube
membrane, the chemists hope to isolate the process of gathering sunlight from
the process of generating hydrogen. This isolation will allow the team to
maximize the system's light-harvesting abilities without altering its
hydrogen-generation abilities, and vice versa. Bren says this is a distinct
advantage over other systems that have integrated designs because in those
designs a change that enhances one trait may degrade another unpredictably and
unacceptably.
Bren says it may be years before the team has a system that
clearly works better than other designs, and even then the system would have to
work efficiently enough to be commercially viable. "But if we succeed, we
may be able to not only help create a fuel that burns cleanly, but the creation
of the fuel itself may be clean."
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