Boston College, MIT researchers achieve dramatic increase in thermoelectric efficiency

“By using nanotechnology, we have found a way to improve an old material by breaking it up and then rebuilding it in a composite of nanostructures in bulk form,” said Boston College physicist Zhifeng Ren, one of the leaders of the project. “This method is low cost and can be scaled for mass production. This represents an exciting opportunity to improve the performance of thermoelectric materials in a cost-effective manner.”

“These thermoelectric materials are already used in many applications, but this better material can have a bigger impact,” said Gang Chen, the Warren and Towneley Rohsenow Professor of Mechanical Engineering at MIT and another leader of the project.

At its core, thermoelectricity is the “hot and cool” issue of physics. Heating one end of a wire, for example, causes electrons to move to the cooler end, producing an electric current. In reverse, applying a current to the same wire will carry heat away from a hot section to a cool section. Phonons, a quantum mode of vibration, play a key role because they are the primary means by which heat conduction takes place in insulating solids.

Bismuth antimony telluride is a material commonly used in thermoelectric products, and the researchers crushed it into a nanoscopic dust and then reconstituted it in bulk form, albeit with nanoscale constituents. The grains and irregularities of the reconstituted alloy dramatically slowed the passage of phonons through the material, radically transforming the thermoelectric performance by blocking heat flow while allowing the electrical flow.

In addition to Ren and six researchers at his BC lab, the international team involved MIT researchers, including Chen and Institute Professor Mildred S. Dresselhaus; research scientist Bed Poudel at GMZ Energy, Inc, a Newton, Mass.-based company formed by Ren, Chen, and CEO Mike Clary; as well as BC visiting Professor Junming Liu, a physicist from Nanjing University in China.

Thermoelectric materials have been used by NASA to generate power for far-away spacecraft. These materials have been used by specialty automobile seat makers to keep drivers cool during the summer. The auto industry has been experimenting with ways to use thermoelectric materials to convert waste heat from a car exhaust systems into electric current to help power vehicles.

The research was supported by the Department of Energy and by the National Science Foundation.

This paper will be published online by the journal Science, at the Science Express web site, on THURSDAY, March 20, 2008. See http://www.sciencexpress.org, and also http://www.aaas.org. Science and Science Express are published by the AAAS, the science society, the world's largest general scientific organization.