SCIENTISTS MAKE PROGRESS IN MAKING FUEL FROM WATER

Fuel from water? A form of Alchemy?
Researchers have been trying for years to
find a limitless, environmentally benign
source of fuel. Now a University of Colorado Boulder
team has developed a radically new
technique that uses the power of sunlight
to efficiently split water into its
components of hydrogen and oxygen,
paving the way for the broad use of
hydrogen as a clean, green fuel.
The CU-Boulder team has devised a solar-
thermal system in which sunlight could be
concentrated by a vast array of mirrors
onto a single point atop a central tower
up to several hundred feet tall. The tower
would gather heat generated by the
mirror system to roughly 2,500 degrees
Fahrenheit (1,350 Celsius), then deliver it
into a reactor containing chemical
compounds known as metal oxides, said
CU-Boulder Professor Alan Weimer,
research group leader.
As a metal oxide compound heats up, it
releases oxygen atoms, changing its
material composition and causing the
newly formed compound to seek out new
oxygen atoms, said Weimer. The team
showed that the addition of steam to the
system -- which could be produced by
boiling water in the reactor with the
concentrated sunlight beamed to the
tower -- would cause oxygen from the
water molecules to adhere to the surface
of the metal oxide, freeing up hydrogen
molecules for collection as hydrogen gas.
"We have designed something here that
is very different from other methods and
frankly something that nobody thought
was possible before," said Weimer of the
chemical and biological engineering
department. "Splitting water with sunlight
is the Holy Grail of a sustainable hydrogen
economy."
One of the key differences between the
CU method and other methods developed
to split water is the ability to conduct two
chemical reactions at the same
temperature, said Musgrave, also of the
chemical and biological engineering
department. While there are no working
models, conventional theory holds that
producing hydrogen through the metal
oxide process requires heating the
reactor to a high temperature to remove
oxygen, then cooling it to a low
temperature before injecting steam to re-
oxidize the compound in order to release
hydrogen gas for collection.
"The more conventional approaches
require the control of both the switching
of the temperature in the reactor from a
hot to a cool state and the introduction of
steam into the system," said Musgrave.
"One of the big innovations in our system
is that there is no swing in the
temperature. The whole process is driven
by either turning a steam valve on or off."
"Just like you would use a magnifying
glass to start a fire, we can concentrate
sunlight until it is really hot and use it to
drive these chemical reactions," said
Muhich. "While we can easily heat it up to
more than 1,350 degrees Celsius, we
want to heat it to the lowest temperature
possible for these chemical reactions to
still occur. Hotter temperatures can cause
rapid thermal expansion and contraction,
potentially causing damage to both the
chemical materials and to the reactors
themselves."