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September 2011

Fuel Breeds Fuel: Recycling Heat

Researchers develop new methods towards commercializing technology to recycle wasted heat

Thomas van der Poll

Recycling is one of the world’s ways of being more conscientious when it comes to consuming resources. However, one resource that is easily overlooked is heat. Every time energy is harnessed to power our cars, refrigerators, laptops, etc., a significant portion of that energy is simply lost as heat to the environment. Instead of letting that heat radiate from everyday tools and appliances, why not recycle it into a useable form?

Researchers in the Center for Energy Efficient Materials are working on thermoelectric, or TE, technology that allows heat to be converted directly into electrical energy, and they have found a way around the harsh conditions required to make an efficient TE device. Not only is their new method milder, but the resulting material performs better.

A TE device has a tailored material sandwiched between two electrodes, each exposed to different temperatures. The properties of the materials in TE devices allow current to flow from hot to cold. Intuitively, a TE material should conduct as little heat as possible to maintain the temperature gradient that drives current flow. Simultaneously, it needs to conduct electricity. A good way to achieve this is using a two-component system, symbiotically enhancing the TE effect.

Previously, the most effective method for making two-component materials was fabricating nanoparticles and supporting them with specialized chemical precursors to allow the nanoparticles to be incorporated into the bulk. While the nanoparticles reduce thermal conductivity -- good for TE materials -- the process used to generate them requires high temperatures. Furthermore, chemical precursors tend to linger in the final product, and that can dramatically bring down the performance of a TE device. Of course, the high temperatures necessary to produce the components imply more energy consumption, which is certainly not desirable. Circumventing these issues is paramount to realizing TE technology on the commercial scale.

At the Center for Energy Efficient Materials, researchers have developed a way to make TE devices at lower temperatures without performance-degrading chemical precursors. Instead, a simpler nanoparticle is used as a structural template, which precludes the high-temperature fabrication of the desired nanoparticle. Using simple redox chemistry, the template particle can be efficiently converted to the desired nanoparticle at room temperature. Another advantage to this method is the material comprising the template particle is compatible with the TE material in a way that will not degrade the performance of the final device. This product can simply be mixed with the second component in powder form and be hot pressed into a two-component solid TE bulk. Practicality is gained both in using milder conditions to produce materials and in increasing the amenability to scale-up. Yet, the icing on the cake is that this new method yields materials that perform twice as well as those prepared using traditional protocol.

One can imagine all the opportunities to implement such a useful energy recycler; however, high-temperatures and chemical precursors make fabricating TE materials expensive and place a limit on how large a scale they can be produced – challenges that keep this technology out of the household. The method developed in the Center for Energy Efficient Materials provides better TE materials at room temperature -- the first step in turning waste heat into a new renewable energy source.

More Information

Zhang Y, H Wang, S Kremer, Y Shi, F Zhang, M Snedaker, K Ding, M Moskovits, GJ Snyder, and GD Stucky. 2011. “Surfactant-Free Synthesis of Bi2Te3−Te Micro−Nano Heterostructure with Enhanced Thermoelectric Figure of Merit.” ACS Nano 5(4), 3158-3165. DOI: 10.1021/nn2002294

Acknowledgments

This work was supported in part by the Center for Energy Efficient Materials, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Basic Energy Sciences, and in part by the National Science Foundation.

About the author(s):

  • A member of the Center for Energy Efficient Materials, an Energy Frontier Research Center, Thomas van der Poll is studying the surface modification of metal oxides used for organic electronics.

More Information

Zhang Y, H Wang, S Kremer, Y Shi, F Zhang, M Snedaker, K Ding, M Moskovits, GJ Snyder, and GD Stucky. 2011. “Surfactant-Free Synthesis of Bi2Te3−Te Micro−Nano Heterostructure with Enhanced Thermoelectric Figure of Merit.” ACS Nano 5(4), 3158-3165. DOI: 10.1021/nn2002294

Disclaimer: The opinions in this newsletter are those of the individual authors and do not represent the views or position of the Department of Energy.