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Scientists discover new way of producing electricity | A team of scientists at MIT has discovered a previously unknown phenomenon that can cause powerful waves of energy to shoot through minuscule wires known as carbon nanotubes, a discovery that could lead to a new way of producing electricity. The phenomenon,
described as thermopower waves, "opens up a new area of energy research, which
is rare," said Michael Strano, MIT's Charles and Hilda Roddey Associate Professor
of Chemical Engineering, who was the senior author of a paper describing the new
findings. Like a collection of flotsam propelled along the surface by waves traveling
across the ocean, it turns out that a thermal wave - a moving pulse of heat -
traveling along a microscopic wire can drive electrons along, creating an electrical
current. The key ingredient in the recipe is carbon nanotubes - submicroscopic
hollow tubes made of a chicken-wire-like lattice of carbon atoms. In the new experiments,
each of these electrically and thermally conductive nanotubes was coated with
a layer of a highly reactive fuel that can produce heat by decomposing. This fuel
was then ignited at one end of the nanotube using either a laser beam or a high-voltage
spark, and the result was a fast-moving thermal wave traveling along the length
of the carbon nanotube like a flame speeding along the length of a lit fuse. According
to Strano, in the group's initial experiments, when they wired up the carbon nanotubes
with their fuel coating in order to study the reaction, "lo and behold, we were
really surprised by the size of the resulting voltage peak" that propagated along
the wire. After further development, the system now puts out energy, in proportion
to its weight, about 100 times greater than an equivalent weight of lithium-ion
battery. While many semiconductor materials can produce an electric potential
when heated, through something called the Seebeck effect, that effect is very
weak in carbon. "There's something else happening here. We call it electron entrainment
since part of the current appears to scale with wave velocity," Strano said. The
thermal wave appears to be entraining the electrical charge carriers (either electrons
or electron holes) just as an ocean wave can pick up and carry a collection of
debris along the surface, he explained. "This important property is responsible
for the high power produced by the system," Strano said. Strano suggests that
one possible application would be in enabling new kinds of ultra-small electronic
devices. Or it could lead to "environmental sensors that could be scattered like
dust in the air," he said. |
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