Things happen differently at the nanoscale, which is one reason why the science of the ultra small keeps turning up fascinating phenomena. The latest discovery is a new sort of electricity, generated when heat waves travelling through carbon nanotubes push electrons along at the same time, creating an electrical current.
This finding “opens up a new era of energy research”, according to Michael Strano, professor of chemical engineering at the Massachusetts Institute of Technology, and one of the scientists who made the discovery of the power of these heat waves – christened thermopower waves – to move electrons around.
The scientists generated the thermopower waves by coating electrically and thermally conductive nanotubes with a layer of a highly reactive fuel. When the fuel is ignited at one end of the nanotube the result is a fast-moving thermal wave travelling along the length of the carbon nanotube. Heat from the fuel goes into the nanotube where it travels thousands of times faster than in the fuel itself.
As this heat feeds back to the fuel coating, a thermal wave is created that is guided along the nanotube. Such is its intensity that it pushes electrons along the tube, creating a substantial electrical current.
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.
According to Strano the amount of power released is much greater than that predicted by thermoelectric calculations. While many semiconductor materials can produce an electric potential when heated, that effect is very weak in carbon. Something else is happening here Strano says. “We call it electron entrainment since part of the current appears to scale with wave velocity.”
In terms of practical applications, it is suggested this new type of electricity could underpin the development of ultra small sensors or medical devices as small as a grain of rice. On the other hand, carbon nanotubes could be fashioned into large arrays to power bigger devices.
Another advantage over traditional batteries, is that ones based on carbon nanotube thermopower would maintain their power indefinitely until used, unlike existing batteries which loose charge when unused.