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 esearchers are developing a new type of environmentally
friendly fuel cell that runs on aluminum and renewable resources
and generates about 20 times more electricity per pound than
car batteries. The cell produces electricity through chemical
reactions between hydrogen peroxide and aluminum. If perfected,
such an electricity source could one day replace conventional
batteries in many applications, including portable electronic
equipment.
 "It
has a huge amount of energy potential," says John Rusek,
an assistant professor of aeronautics and astronautics at Purdue
University, who is working with students to develop the cell.
A poster paper about the research was presented in November,
during the Second International Hydrogen Peroxide Propulsion
Conference at Purdue.
Hydrogen peroxide,
or H2O2, also offers promise in developing low-cost, nontoxic
rocket fuels. The chemical differs from water only in that it
contains two oxygen atoms. It is relatively easy to manufacture
-- in principle it could be made from water -- and it is far
less dangerous or expensive than conventional "oxidizers,"
such as liquid oxygen, which are needed to burn rocket fuels.
"It is
actively being studied together with new types of nontoxic propellants
made from alcohol that offer promise as alternatives to the conventional
petroleum-based rocket fuels," Rusek says.
Engineers
hope to have hydrogen-peroxide-based rockets in operation within
a decade. But at least one visionary couldn't wait that long.
Richard Brown, a British engineer, became the fastest man on
two wheels in September, when his Gillette Mach 3 Challenger
rocket-powered motorcycle hit 365 miles per hour at the Bonneville
Salt Flats.
"All
I can say is the G force is absolutely obscene," Brown,
34, told researchers during the hydrogen peroxide conference.
The 26-foot-long vehicle was powered by rockets that used hydrogen
peroxide as an oxidizer.
Unlike the
hydrogen peroxide that is found in drugstores, which is about
97 percent water, the rocket-propulsion variety has just the
opposite concentration -- 3 percent water and 97 percent hydrogen
peroxide -- and it has had critical contaminants removed, says
Stephen Heister, a professor of aeronautics and astronautics
at Purdue.
This purified,
concentrated form of H2O2 is then broken down with chemical catalysts,
yielding oxygen that combusts with alcohol-based fuels, such
as methanol or ethanol, which can be derived from corn. Such
a propulsion system would provide an alternative to today's nonrenewable
hydrocarbon fuels that are processed from crude oil, Heister
says.
In the fuel
cells, hydrogen peroxide serves two roles: it is a "catholyte,"
meaning it is both the electrolyte -- a liquid that conducts
electricity and allows the reaction to occur -- and it is the
cathode, or the portion of the battery that attracts electrons.
The aluminum serves as the cell's fuel and its anode; as it oxidizes,
it gives up electrons. Waste products include water and recyclable
chemical compounds.
Serendipity
has helped the Purdue researchers overcome a major obstacle in
the fuel cell work. Earlier attempts by the US Navy to develop
the cells were abandoned because the reaction with aluminum quickly
formed a thick sludge that hindered the flow of electricity.
However, because the Purdue engineers didn't have pure aluminum
for their work, they used an aluminum alloy. To their surprise,
they found that the alloy did not form the sludge, Rusek says.
One problem
with the experimental cells is that, unlike batteries, they do
not immediately provide a steady supply of electricity; it takes
about two hours for the cells to reach their peak electrical
output before producing a steady current flow, says engineering
student Kok Hong Lim, a junior from Singapore who is majoring
in aeronautics and astronautics. Future work will include research
aimed at correcting that problem, he says.
Aluminum was
chosen originally because it is an abundant natural resource
and is readily available from recycled sources, says Rusek, who
estimates that the cells are at least 20 times higher in energy
density than a standard lead-acid car battery.
"That
means a 20-kilogram lead-acid battery would put out the same
amount of energy as a one-kilogram hydrogen peroxide fuel cell,"
he says, noting that other metals, such as lithium alloys, might
also work in hydrogen peroxide fuel cells. 
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uns.purdue.edu.