Solar energy storage from nanotubes

Nanofabrication enables the production of tailor-made chemical storage materials

Light battery © Grossman / MIT
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American researchers have discovered a new way to chemically store the energy of sunlight. An effective "light-battery" proved to be a combination of carbon nanotubes and an organic ring molecule. Illuminated by light, this complex changes its structure to a more energetic form. Only when he receives another stimulus, the structure returns to the old form. She returns the stored energy as heat.

"You have a material that transforms and stores energy. It's tough, it does not degrade and it's cheap, "says Alexie Kolpak of the Massachusetts Institute of Technology (MIT). A big advantage is the high energy density of the connection: It corresponds to that of a conventional lithium-ion battery. This allows the nanotube compound to store 10, 000 times more energy at the same volume than previous light-storage materials. In contrast to these, the new material also comes without the precious and succinct element ruthenium.

However, there is still a restriction, say the researchers in the journal "Nano Letters": The nanotube storage is well suited for heat production. In order to gain power from sunlight with it, however, another conversion step - for example a steam turbine - would have to be added downstream.

Chemical storage previously too unstable or too expensive

The conversion to chemical energy is considered a good way to save the solar energy relatively low loss for a long time. However, according to the MIT researchers, a suitable material is still lacking so far. Some molecules disintegrate after a few cycles of picking up and dispensing, others are too expensive. Now Kolpak and her colleagues could have developed a chemical solar energy storage that is both cheap and stable.

Nanotubes as a construction aid

The material developed by the researchers consists of carbon nanotubes as a backbone. At these azobenzenes are attached, ring-shaped hydrocarbons. This compound has "new properties that are not achievable in the single molecules, " says Working Group Leader Jeffrey Grossman. display

Decisive for the good properties as an energy storage is the energy gap between the two stable states - low energy and high energy - that could take the molecule. If the gap is too small, the molecule falls back to its ground state too easily and fails as a memory. If the gap is too big, it will not restore its energy easily. "Using nanotechnology, you can control how much energy a molecule can store and how long, " says Kolpak.

Energy density can be significantly increased

"The novelty of this work is that it shows how energy density can be significantly increased, " commented Yosuke Kanai of the University of North Carolina. This innovative idea opens up an interesting opportunity to tailor well-known photoactive molecules for solar thermal applications and storage.

"I see this only as the tip of an iceberg, " says MIT researcher Grossman. He and his team are already actively looking at a range of new materials as potential solar energy storage. (Nano Letters, 2011; DOI: 10.1021 / nl201357n)

(Nano Letters / Massachusetts Institute of Technology / dapd, 15.07.2011 - NPO)