Researchers at Purdue University
have further developed a technology that could
represent a pollution-free energy source for a range
of potential applications, from golf carts to
submarines and cars to emergency portable generators.
The technology produces hydrogen by adding water to
an alloy of aluminum and gallium. When water is added
to the alloy, the aluminum splits water by attracting
oxygen, liberating hydrogen in the process. The Purdue
researchers are developing a method to create
particles of the alloy that could be placed in a tank
to react with water and produce hydrogen on demand.
The gallium is a critical component because it
hinders the formation of an aluminum oxide skin
normally created on aluminum's surface after bonding
with oxygen, a process called oxidation. This skin
usually acts as a barrier and prevents oxygen from
reacting with aluminum. Reducing the skin's protective
properties allows the reaction to continue until all
of the aluminum is used to generate hydrogen, said
Jerry Woodall, a distinguished professor of electrical
and computer engineering at Purdue who invented the
process.
Since the technology was first announced in May,
researchers have developed an improved form of the
alloy that contains a higher concentration of
aluminum.
Recent findings are detailed in the first research
paper about the work, which will be presented on Sept.
7 during the 2nd Energy Nanotechnology International
Conference in Santa Clara, Calif. The paper was
written by Woodall, Charles Allen and Jeffrey Ziebarth,
both doctoral students in Purdue's School of
Electrical and Computer Engineering.
Because the technology could be used to generate
hydrogen on demand, the method makes it unnecessary to
store or transport hydrogen - two major obstacles in
creating a hydrogen economy, Woodall said.
The gallium component is inert, which means it can
be recovered and reused.
"This is especially important because of the
currently much higher cost of gallium compared with
aluminum," Woodall said. "Because gallium can be
recovered, this makes the process economically viable
and more attractive for large-scale use. Also, since
the gallium can be of low purity, the cost of impure
gallium is ultimately expected to be many times lower
than the high-purity gallium used in the electronics
industry."
As the alloy reacts with water, the aluminum turns
into aluminum oxide, also called alumina, which can be
recycled back into aluminum. The recycled aluminum
would be less expensive than mining the metal, making
the technology more competitive with other forms of
energy production, Woodall said.
In recent research, the engineers rapidly cooled
the molten alloy to make particles that were 28
percent aluminum by weight and 72 percent gallium by
weight. The result was a "metastable solid alloy" that
also readily reacted with water to form hydrogen,
alumina and heat, Woodall said.
Following up on that work, the researchers
discovered that slowly cooling the molten alloy
produced particles that contain 80 percent aluminum
and 20 percent gallium.
"Particles made with this 80-20 alloy have good
stability in dry air and react rapidly with water to
form hydrogen," Woodall said. "This alloy is under
intense investigation, and, in our opinion, it can be
developed into a commercially viable material for
splitting water."
The technology has numerous potential applications.
Because the method makes it possible to use hydrogen
instead of gasoline to run internal combustion
engines, it could be used for cars and trucks.
Combusting hydrogen in an engine or using hydrogen to
drive a fuel cell produces only water as waste.
"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," Woodall said.
The U.S. Department of Energy has set a goal of
developing alternative fuels that possess a "hydrogen
mass density" of 6 percent by the year 2010 and 9
percent by 2015. The percent mass density of hydrogen
is the mass of hydrogen contained in the fuel divided
by the total mass of the fuel multiplied by 100.
Assuming 50 percent of the water produced as waste is
recovered and cycled back into the reaction, the new
80-20 alloy has a hydrogen mass density greater than 6
percent, which meets the DOE's 2010 goal.
Aluminum is refined from the raw mineral bauxite,
which also contains gallium. Producing aluminum from
bauxite results in waste gallium.
"This technology is feasible for commercial use,"
Woodall said. "The waste alumina can be recycled back
into aluminum, and low-cost gallium is available as a
waste product from companies that produce aluminum
from the raw mineral bauxite. Enough aluminum exists
in the United States to produce 100 trillion kilowatt
hours of energy. That's enough energy to meet all the
U.S. electric needs for 35 years. If impure gallium
can be made for less than $10 a pound and used in an
onboard system, there are enough known gallium
reserves to run 1 billion cars."
The researchers note in the paper that for the
technology to be used to operate cars and trucks, a
large-scale recycling program would be required to
turn the alumina back into aluminum and to recover the
gallium.
"In the meantime, there are other promising
potential markets, including lawn mowers and personal
motor vehicles such as golf carts and wheelchairs,"
Woodall said. "The golf cart of the future, three or
four years from now, will have an aluminum-gallium
alloy. You will add water to generate hydrogen either
for an internal combustion engine or to operate a fuel
cell that recharges a battery. The battery will then
power an electric motor to drive the golf cart."
Another application that is rapidly being developed
is for emergency portable generators that will use
hydrogen to run a small internal combustion engine.
The generators are likely to be on the market within a
year, Woodall said.
The technology also could make it possible to
introduce a non-polluting way to idle diesel trucks.
Truck drivers idle their engines to keep power flowing
to appliances and the heating and air conditioning
systems while they are making deliveries or parked,
but such idling causes air pollution, which has
prompted several states to restrict the practice.
The new hydrogen technology could solve the
truck-idling dilemma.
"What we are proposing is that the truck would run
on either hydrogen or diesel fuel," Woodall said.
"While you are on the road you are using the diesel,
but while the truck is idling, it's running on
hydrogen."
The new hydrogen technology also would be
well-suited for submarines because it does not emit
toxic fumes and could be used in confined spaces
without harming crew members, Woodall said.
"You could replace nuclear submarines with this
technology," he said.
Other types of boats, including pleasure craft,
also could be equipped with such a technology.
"One reason maritime applications are especially
appealing is that you don't have to haul water,"
Woodall said.
The Purdue researchers had thought that making the
process competitive with conventional energy sources
would require that the alumina be recycled back into
aluminum using a dedicated infrastructure, such as a
nuclear power plant or wind generators. However, the
researchers now know that recycling the alumina would
cost far less than they originally estimated, using
standard processing already available.
"Since standard industrial technology could be used
to recycle our nearly pure alumina back to aluminum at
20 cents per pound, this technology would be
competitive with gasoline," Woodall said. "Using
aluminum, it would cost $70 at wholesale prices to
take a 350-mile trip with a mid-size car equipped with
a standard internal combustion engine. That compares
with $66 for gasoline at $3.30 per gallon. If we used
a 50 percent efficient fuel cell, taking the same trip
using aluminum would cost $28."
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.
In 1967, while working as a researcher at IBM,
Woodall discovered that liquid alloys of aluminum and
gallium spontaneously produce hydrogen if mixed with
water. 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 television remote
controls and new types of lighting 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.
Also while at IBM, Woodall and research engineer
Jerome Cuomo were issued a U.S. patent in 1982 for a
"solid state, renewable energy supply." The patent
described their discovery that when aluminum is
dissolved in liquid gallium just above room
temperature, the liquid alloy readily reacts with
water to form hydrogen, alumina and heat.
Future research will include work to further
perfect the solid alloy and develop systems for the
controlled delivery of hydrogen.
The 2nd Energy Nanotechnology International
Conference is sponsored by the American Society of
Mechanical Engineers and ASME Nanotechnology
Institute.
|
Source:
Purdue
University
Published on
31st August 2007
Related
links>>
|
Advertisement
 |
