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Engineers Develop Nanotech Solar Thermal Fuel Cell

Carbon nanotube illustration (National Science Foundation)

Carbon nanotube illustration (National Science Foundation)

Researchers at Massachusetts Institute of Technology have developed a process for storing solar energy in the form of heat with a material based on carbon nanotubes. A description of the process by engineering professor Jeffrey Grossman and postdoc Alexie Kolpak appears online in the journal Nano Letters (paid subscription required).

Grossman and Kolpak’s methods involve storing the sun’s heat in chemical form. In principle, capturing solar heat in a chemical has advantages, since the chemical material can be stored for long periods of time without losing any of its stored energy.

Until now, however, the chemicals needed to perform this conversion and storage either degraded within a few cycles. Other methods involved the element ruthenium, which is rare and still expensive, almost $200.00 an ounce.

The new material found by Grossman and Kolpak is made with carbon nanotubes, tiny tubular structures of pure carbon, in combination with a compound called azobenzene. The molecules that result use nanoscale templates — one nanometer equals one billionth of a meter — to shape and constrain their physical structure, and gain new properties not in the raw materials making up this new compound.

The authors say this new chemical system is less expensive than earlier ruthenium-containing compounds, but also more efficient at storing energy in a given amount of space. Its energy density, says Kolpak, is about 10,000 times higher than ruthenium-based materials, comparable to lithium-ion batteries.

In this process, solar energy is stored in molecules whose structure changes when exposed to sunlight, and can remain stable in that form. When nudged by a a catalyst, small temperature change, or a flash of light, the altered molecules revert back to their earlier form, releasing stored energy as heat (not electricity).

The process developed by Grossman and Kolpak combines energy harvesting and storage into a single step. Grossman describes it as a rechargeable heat battery with a long shelf life, like a conventional battery.

Read more: Engineers Develop Efficient Nanotech Solar Energy Film

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