MIT finds new way to make electricity

Posted by Emma Woollacott

MIT researchers have discovered a completely new way of producing electricity - and they don't fully understand how it works.

A previously unknown phenomenon dubbed 'thermopower waves' causes powerful waves of energy to shoot through carbon nanotubes.

The discovery "opens up a new area of energy research, which is rare," says senior author Michael Strano of MIT.

Just as flotsam is propelled along the surface by waves traveling across the ocean, it seems a thermal wave — a moving pulse of heat — traveling along a microscopic wire can drive electrons along, creating an electrical current.

Electrically and thermally conductive nanotubes were coated with a layer of a highly reactive fuel. When this was ignited, a fast-moving thermal wave traveled along the length of the carbon nanotube like a flame along a lit fuse.

But the heating produced by that combustion, it turns out, also pushes electrons along the tube, creating a substantial electrical current. The system puts out energy about 100 times greater than an equivalent weight of lithium-ion battery.

The amount of power released, says Strano, is much greater than that predicted by thermoelectric calculations.

"There's something else happening here," he says. "We call it electron entrainment since part of the current appears to scale with wave velocity."

The thermal wave, he explains, appears to be entraining the electrical charge carriers, just as an ocean wave can pick up and carry debris. The team suspects this is what's responsible for the high power.

Because this is such a new discovery, says Strano, it's hard to predict exactly what the practical applications will be. But he suggests that one possible application would be in enabling new kinds of ultra-small electronic devices — the size of grains of rice.

In theory, he says, such devices could maintain their power indefinitely until used, unlike batteries whose charge leaks away gradually as they sit on a shelf.

And while the individual nanowires are tiny, Strano suggests that they could be made in large arrays in order to supply significant amounts of power for larger devices.