Although we are great fans of atomically precise nanotechnology, sometimes random nanostructures can be surprisingly useful. An economical nanotech procedure—ball milling followed by hot pressing—recasts a commercially available material as a composite of random nanostructures that efficiently converts waste heat into electricity. Excerpts from a report by Katherine Bourzacat at Technology Review: “Cheap, Efficient Thermoelectrics: Nanomaterials could be used for lower-emission cars and solar panels“:
Thermoelectric materials promise everything from clean power for cars to clean power from the sun, but making these materials widely useful has been a challenge. Now researchers at MIT and Boston College have developed an inexpensive, simple technique for achieving a 40 percent increase in the efficiency of a common thermoelectric material. Thermoelectric materials, which can convert heat into electricity and electricity into heat, hold promise for turning waste heat into power. But thermoelectric materials have not been efficient enough to move beyond niche applications. The new jump in efficiency, achieved with a relatively inexpensive material, may finally make possible such applications as solar panels that turn the sun’s heat into electricity, and car exhaust pipes that use waste heat to power the radio and air conditioner.
The researchers started with bismuth antimony telluride, a thermoelectric material used in niche products such as picnic coolers and cooling car seats. Then Gang Chen, a professor of mechanical engineering at MIT; Institute Professor Mildred Dresselhaus; and Boston College physics professor Zhifeng Ren crushed it into a powder with a grain size averaging about 20 nanometers, and pressed it into discs and bars at high heat. The resulting material has a much finer crystalline lattice structure than the original material, which is made up of millimeter-scale grains. Chen and Ren’s nanocomposite formulation of the material is 40 percent more efficient than the conventional form of the material at 100 °C, and it works at temperatures ranging from room temperature to 250 °C.
“Power-generation applications [for thermoelectrics] are not big now because the materials aren’t good enough,” says Chen. He believes that his group’s more efficient version of the material will finally make such applications commercially viable.
…Ren says that it’s easy to make large amounts of the nanocomposite material: “We’re not talking grams; we’re not talking kilograms. We can make metric tons.” Because bismuth antimony telluride is already used in commercial products, Ren and Chen predict that their technique will be integrated into commercial manufacturing in several months.
Additional details and explanations can be found in coverage at ScienceDaily, at New Scientist, and at IEEE Spectrum online: “Nano-breakthrough: Dramatic Increase In Thermoelectric Efficiency Heralds New Era In Heating, Cooling And Power Generation” and “Reincarnated material turns waste heat into power” and “Random Nanostructure Boosts Thermoelectric Power“. The research was published in Science (abstract).
—Jim
