Purdue Process Generates Hydrogen from Aluminum Alloy
Water added to aluminum mixed with Gallium can produce hydrogen
on demand. As a catalyst, the Gallium is not consumed. The oxidized
aluminum can be recycled. The process is close to being cost competitive
with petrol.
adapted from press release
Purdue researchers demonstrate their
method for producing hydrogen by adding water to an alloy of
aluminum and gallium. The hydrogen could then be used to run an
internal combustion engine. The reaction was discovered by Jerry
Woodall, center, a distinguished professor of electrical and
computer engineering. Charles Allen, holding test tube, and Jeffrey
Ziebarth, both doctoral students in the School of Electrical and
Computer Engineering, are working with Woodall to perfect the
process.
(Purdue News Service photo/David Umberger) |
WEST LAFAYETTE, INDIANA, USA -- A Purdue University engineer has
developed a method that uses an aluminum alloy to extract hydrogen from
water for running fuel cells or internal combustion engines. The
technique could be used to replace gasoline, though it is not quite
cost-competitive yet.
The method makes it unnecessary to store or transport hydrogen - two
major challenges in creating a hydrogen economy, said Jerry Woodall, a
distinguished professor of electrical and computer engineering at Purdue
who invented the process.
"The hydrogen is generated on demand, so you only produce as much as you
need when you need it," said Woodall, who presented research findings
detailing how the system works during a recent energy symposium at
Purdue.
The technology could be used to drive small internal combustion
engines in various applications, including portable emergency
generators, lawn mowers and chain saws. The process could, in theory,
also be used to replace gasoline for cars and trucks, he said.
Hydrogen is generated spontaneously when water is added to pellets of
the alloy, which is made of aluminum and a metal called gallium. The
researchers have shown how hydrogen is produced when water is added to a
small tank containing the pellets. Hydrogen produced in such a system
could be fed directly to an engine, such as those on lawn mowers.
"When water is added to the pellets, the aluminum in the solid alloy
reacts because it has a strong attraction to the oxygen in the water,"
Woodall said.
This reaction splits the oxygen and hydrogen contained in water,
releasing hydrogen in the process.
The gallium is critical to the process because it hinders the formation
of a skin normally created on aluminum's surface after oxidation. This
skin usually prevents oxygen from reacting with aluminum, acting as a
barrier. Preventing the skin's formation allows the reaction to continue
until all of the aluminum is used.
The waste products are gallium and aluminum oxide, also called alumina.
Combusting hydrogen in an engine produces only water as waste.
As a catalyst, the gallium is not consumed, and hence does not need to
be replenished. The alumina can be recharged in a separate process,
preferably using renewable energy.
The Purdue Research Foundation holds title to the primary patent, which
has been filed with the U.S. Patent and Trademark Office and is pending.
An Indiana startup company, AlGalCo LLC., has received a license for the
exclusive right to commercialize the process.
Woodall discovered that liquid alloys of aluminum and gallium
spontaneously produce hydrogen if mixed with water while he was working
as a researcher in the semiconductor industry in 1967. The research,
which focused on developing new semiconductors for computers and
electronics, led to advances in optical-fiber communications and
light-emitting diodes, making them practical for everything from DVD
players to automotive dashboard displays. That work also led to
development of advanced transistors for cell phones and components in
solar cells powering space modules like those used on the Mars rover,
earning Woodall the 2001 National Medal of Technology from President
George W. Bush.
"I was cleaning a crucible containing liquid alloys of gallium and
aluminum," Woodall said. "When I added water to this alloy - talk about
a discovery - there was a violent poof. I went to my office and worked
out the reaction in a couple of hours to figure out what had happened.
When aluminum atoms in the liquid alloy come into contact with water,
they react, splitting the water and producing hydrogen and aluminum
oxide.
"Gallium is critical because it melts at low temperature and readily
dissolves aluminum, and it renders the aluminum in the solid pellets
reactive with water. This was a totally surprising discovery, since it
is well known that pure solid aluminum does not readily react with
water."
"No toxic fumes are produced," Woodall said. "It's important to note
that the gallium doesn't react, so it doesn't get used up and can be
recycled over and over again. The reason this is so important is because
gallium is currently a lot more expensive than aluminum. Hopefully, if
this process is widely adopted, the gallium industry will respond by
producing large quantities of the low-grade gallium required for our
process. Currently, nearly all gallium is of high purity and used almost
exclusively by the semiconductor industry."
Woodall said that because the technology makes it possible to use
hydrogen instead of gasoline to run internal combustion engines it could
be used for cars and trucks. In order for the technology to be
economically competitive with gasoline, however, the cost of recycling
aluminum oxide must be reduced, he said.
"Right now it costs more than $1 a pound to buy aluminum, and, at that
price, you can't deliver a product at the equivalent of $3 per gallon of
gasoline," Woodall said.
However, the cost of aluminum could be reduced by recycling it from the
alumina using a process called fused salt electrolysis. The aluminum
could be produced at competitive prices if the recycling process were
carried out with electricity generated by a nuclear power plant or
windmills. Because the electricity would not need to be distributed on
the power grid, it would be less costly than power produced by plants
connected to the grid, and the generators could be located in remote
locations, which would be particularly important for a nuclear reactor
to ease political and social concerns, Woodall said.
"The cost of making on-site electricity is much lower if you don't have
to distribute it," Woodall said.
The approach could enable the United States to replace gasoline for
transportation purposes, reducing pollution and the nation's dependence
on foreign oil. If hydrogen fuel cells are perfected for cars and trucks
in the future, the same hydrogen-producing method could be used to power
them, he said.
"We call this the aluminum-enabling hydrogen economy," Woodall said.
"It's a simple matter to convert ordinary internal combustion engines to
run on hydrogen. All you have to do is replace the gasoline fuel
injector with a hydrogen injector."
Even at the current cost of aluminum, however, the method would be
economically competitive with gasoline if the hydrogen were used to run
future fuel cells.
"Using pure hydrogen, fuel cell systems run at an overall efficiency of
75 percent, compared to 40 percent using hydrogen extracted from fossil
fuels and with 25 percent for internal combustion engines," Woodall
said. "Therefore, when and if fuel cells become economically viable, our
method would compete with gasoline at $3 per gallon even if aluminum
costs more than a dollar per pound."
The hydrogen-generating technology paired with advanced fuel cells also
represents a potential future method for replacing lead-acid batteries
in applications such as golf carts, electric wheel chairs and hybrid
cars, he said.
The technology underscores aluminum's value for energy production.
"Most people don't realize how energy intensive aluminum is," Woodall
said. "For every pound of aluminum you get more than two kilowatt hours
of energy in the form of hydrogen combustion and more than two kilowatt
hours of heat from the reaction of aluminum with water. A midsize car
with a full tank of aluminum-gallium pellets, which amounts to about 350
pounds of aluminum, could take a 350-mile trip and it would cost $60,
assuming the alumina is converted back to aluminum on-site at a nuclear
power plant.
"How does this compare with conventional technology? Well, if I put
gasoline in a tank, I get six kilowatt hours per pound, or about two and
a half times the energy than I get for a pound of aluminum. So I need
about two and a half times the weight of aluminum to get the same energy
output, but I eliminate gasoline entirely, and I am using a resource
that is cheap and abundant in the United States. If only the energy of
the generated hydrogen is used, then the aluminum-gallium alloy would
require about the same space as a tank of gasoline, so no extra room
would be needed, and the added weight would be the equivalent of an
extra passenger, albeit a pretty large extra passenger."
The concept could eliminate major hurdles related to developing a
hydrogen economy. Replacing gasoline with hydrogen for transportation
purposes would require the production of huge quantities of hydrogen,
and the hydrogen gas would then have to be transported to filling
stations. Transporting hydrogen is expensive because it is a "non-ideal
gas," meaning storage tanks contain less hydrogen than other gases.
"If I can economically make hydrogen on demand, however, I don't have to
store and transport it, which solves a significant problem," Woodall
said.
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