Researchers discover new way of producing electricity

A team of scientists at Massachusetts Institute of Technology (MIT) recently discovered a previously unknown phenomenon that can cause powerful waves of energy to shoot through minuscule wires known as carbon nanotubes. The discovery could lead to a new way of producing electricity, the researchers say.

“The phenomenon, described as thermo-power waves, opens up a new area of energy research,” says Michael Strano, MIT’s Charles and Hilda Roddey Associate Professor of Chemical Engineering. “It turns out that a thermal wave - a moving pulse of heat - travelling along a microscopic wire can drive electrons along, creating an electrical current.”

The key ingredient is carbon nanotubes - sub-microscopic hollow tubes made of a ‘chicken-wire-like’ lattice of carbon atoms, just a few nanometres (billionths of a metre) in diameter.

In the experiments, electrically and thermally conductive carbon nanotubes were coated with a layer of a reactive fuel that can produce heat by decomposing. This fuel was then ignited at one end of the nanotube using either a laser or a high-voltage spark, resulting in a fast-moving thermal wave travelling along the length of the nanotube like a flame speeding along the length of a lit fuse. Heat from the fuel goes into the nanotube, where it travels thousands of times faster than in the fuel itself. As the heat feeds back to the fuel coating, a thermal wave is created along the nanotube. The heat speeds along the tube 10,000 times faster than the normal spread of this chemical reaction. The heating produced by that combustion also pushes electrons along the tube, creating a substantial electrical current.

The size of the resultant voltage peak that propagated along the wire surprised the research team. 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.

Possible applications

“Because this is such a new discovery, it’s hard to predict exactly what the practical applications will be,” Strano adds. “But one possible application would be in enabling new kinds of ultrasmall electronic devices, perhaps with sensors or treatment devices that could be injected into the body or environmental sensors that could be scattered like dust in the air.”

In theory, such devices could maintain their power indefinitely until used, unlike batteries whose charges leak away gradually as they sit unused. And while the individual nanowires are tiny, Strano suggests that they could be made in large arrays to supply significant amounts of power for larger devices.

The researchers also plan to pursue another aspect of their theory: that by using different kinds of reactive materials for the coating, the wave-front could oscillate, thus producing an alternating current. That would open up a variety of possibilities, because alternating current is the basis for radio waves such as cell phone transmissions, but present energy-storage systems all produce direct current.

The team also plans to work on improving the efficiency of the present versions of the system, which are currently low, because considerable power is given off as heat and light.