MIT scientists develop thermopower waves

- A team of scientists at MIT has discovered a new way to generate power with carbon nanotubes.

In a paper titled "Chemically driven carbon-nanotube-guided thermopower waves" published in Nature Materials, they describe how they made "thermopower waves" flow through the nanotubes, generating a significant amount of power relative to the size of the nanotubes. This opens up new areas of research in energy generation and storage.

In the new experiments, each of these electrically and thermally conductive nanotubes was 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 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. 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 that is guided along the nanotube. With a temperature of 3,000 kelvins, this ring of heat speeds along the tube 10,000 times faster than the normal spread of this chemical reaction. The heating produced by that combustion, it turns out, also 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.

What's surprising about this is that the amount of power released is much higher than what standard thermoelectric calculations predict. Something is going on with carbon nanotubes when they are heated up that isn't happening on the same scale with other semi-conductors.

The researchers suggest that these specially coated carbon nanotubes could be used to power extremely small devices and sensors. These could be used to gather environmental data out in the field and help us better understand our planet and its ecosystems, for example. The beauty would be that unlike regular batteries, the energy would not leak out with time, it would only go down when the device is in use.

The technology could also be scaled up to power larger devices, but this seems technically challenging on many levels. How do you re-coat the nanotubes once the fuel has been used? Would this lead to very energy-dense one-time-use batteries? If the fuel doesn't leave behind toxic by-products and it's not too hard to re-coat the nanotubes, maybe this could make sense. But if the fuel is toxic and the nanotubes are hard to re-coat, do we want this on a large scale?

We'll have to wait to see if the technology can be refined enough to have real-world uses. With some luck, this is just the start of a long chain of discoveries that will lead to a world-changing energy storage solution.