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LAFAYETTE, Ind. – Engineers at Purdue University
have developed a new way of producing hydrogen for
fuel cells to automatically recharge batteries in
portable electronics, such as notebook computers, and eliminate the need to
use a wall outlet.
The findings will be presented Sunday (Aug. 28)
during the annual meeting
of the American Chemical Society in Washington,
D.C., and also will be detailed in a peer-reviewed
paper to appear in an upcoming issue of the journal
Combustion and Flame. The paper was written by research
scientist Evgeny Shafirovich, postdoctoral research
associate Victor Diakov and Arvind
Varma , the R. Games Slayter Distinguished Professor
of Chemical Engineering and head of Purdue's School
of Chemical Engineering.
The researchers developed the new method earlier
this year and envision a future system in which pellets
of hydrogen-releasing material would be contained
in disposable credit-card-size cartridges. Once the
pellets were used up, a new cartridge would be inserted
into devices such as cell phones, personal digital
assistants, notebook computers, digital cameras,
handheld medical diagnostic devices and defibrillators.
The method also might have military applications
in portable electronics for soldiers and for equipment
in spacecraft and submarines, Varma said.
The new technique combines two previously known
methods for producing hydrogen. The previous methods
have limitations making them impractical when used
alone, but those drawbacks are overcome when the
methods are combined, Varma said.
One of the methods was invented by Herbert C. Brown,
a chemist and Nobel laureate from Purdue who discovered
a compound called sodium borohydride during World
War II. The compound contains sodium, boron and hydrogen.
He later developed a technique for producing hydrogen
by combining sodium borohydride with water and a
catalyst. The method, however, has a major drawback
because it requires expensive catalysts such as ruthenium.
The other method involves a chemical reaction in
which tiny particles of aluminum are combined with
water in such a way that the aluminum ignites, releasing
hydrogen during the combustion process. This method
does not require an expensive catalyst, but it yields
insufficient quantities of hydrogen to be practical
for fuel cell applications.
"Our solution is to combine both methods by using
what we call a triple borohydride-metal-water mixture,
which does not require a catalyst and has a high
enough hydrogen yield to make the method promising
for fuel cell applications," Varma said. "So far
we have shown in experiments that we can convert
6.7 percent of the mixture to hydrogen, which means
that for every 100 grams of mixture we can produce
nearly 7 grams of hydrogen, and that yield is already
better than alternative methods on the market."
The researchers have filed a provisional patent
application for the technique and hope to increase
the yield to about 10 percent through additional
experiments, Shafirovich said.
Hydrogen produced by the method could be used to
drive a fuel cell, which then would produce electricity
to charge a battery. A computer chip would automatically
detect when the battery needed to be recharged, activating
a new pellet until all of the pellets on the cartridge
were consumed. Byproducts from the reaction are environmentally
benign and can either be safely discarded or recycled,
Diakov said.
In addition to its potential use in portable electronics,
the technology offers promise as an energy source
to power hardware in spacecraft.
"The Apollo 13 accident was caused by an explosion
involving liquid oxygen, which is needed along with
liquid hydrogen to feed a fuel cell in spacecraft," Shafirovich
said. "Use of chemical mixtures, such as ours, for
generation of hydrogen and oxygen would eliminate
the possibility of such an explosion."
A key step in the hydrogen-producing reaction is
the use of tiny particles of aluminum only about
as wide as 100 nanometers, or 100 billionths of a
meter.
"You don't want to use large lumps of aluminum because
then you only get reactions on the outer surfaces
of those lumps, so you don't produce enough hydrogen," Varma
said. "What you would rather use is tiny particles
that have a high surface area, which enables them
to completely react, leaving no waste and producing
more hydrogen."
Another crucial component is a special gel created
by combining water with a material called polyacrylamide.
"If you want to ignite a mixture of aluminum with
water, the problem is that water boils at 100 degrees
Centigrade and aluminum ignites at a much higher
temperature," Shafirovich said. "So, if you try to
ignite the mixture you just vaporize water and the
aluminum doesn't ignite.
"When
we use this gel, water boils at a much higher temperature,
and the nanoscale powder also decreases the ignition
temperature of aluminum. So you are both increasing
the boiling point of water and decreasing the ignition
temperature of aluminum, making the reaction possible."
The researchers believe they will be able to safely
dissipate the heat produced by the reaction, making
the technology practical for portable electronics.
This research is supported by the Purdue Hydrogen
Economy initiative of the College of Engineering
and is being conducted as a part of Purdue's new
Energy Center, created this year at the university's
Discovery Park.
Writer: Emil Venere, (765) 494-4709, venere@purdue.edu
Sources: Arvind Varma, 765 494-4075, avarma@purdue.edu
Evgeny Shafirovich, (765) 496-2969, eshafir@purdue.edu
Victor Diakov, diakov@purdue.edu
Purdue News Service: (765) 494-2096; purduenews@purdue.edu
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