Capacitors store electric charge, and supercapacitors
are capable of delivering a large amount of energy in a short time --
something that is beyond regular batteries.
Researchers at the University of California at Davis and Mytitek
Incorporated have found a relatively simple and inexpensive way to form
a new type of thin film supercapacitor from multi-wall carbon nanotubes.
Carbon nanotubes are rolled-up sheets of carbon; multi-wall carbon
nanotubes are sets of nested nanotubes. Nanotubes make good electrodes
for super capacitors because they are highly conductive and have large
surface areas for trapping electric charges.
The nanotube capacitors could eventually be used in electric and
hybrid vehicles, space applications, cell phones, and lightweight electronic
fuses; they would be especially appropriate for providing the needed surge
of startup power for fuel cells, according to the researchers.
The researchers' prototype supercapacitor produced a power density
of 30 kilowatts per kilogram, which is seven and a half times the power
of today's commercial supercapacitors, according to the researchers. Other
researchers have achieved power densities of 20 kilowatts per kilogram,
but they use more expensive single-wall carbon nanotubes and a fabrication
process that required heating, according to the researchers.
The process to make the multi-wall nanotube supercapacitor film
is simple, and thus potentially inexpensive. The researchers deposited
high concentrations of nanotubes suspended in liquid on nickel films and
dried them at room temperature. The nanotubes ended up densely packed
and partially aligned.
The super capacitors could be ready for practical use within one
to five years, according to the researchers. The work appeared in the
February 1, 2005 issue of Nanotechnology.
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