Going nano boosts thermoelectrics

Thermoelectric materials take advantage of the temperature difference between a pair of materials that conduct electricity. Heat one of the materials while cooling the other and electricity flows. Conversely, send electricity through the circuit and one end of the material heats up while the other cools down.

Researchers from the University of Wollongong in Australia, the University of New South Wales in Australia, and the University of Oregon have shown how a thermoelectric material should be designed to reach its maximum possible efficiency.

Conventional wisdom has until now said that thermoelectric devices could not come near their optimum efficiency because they involve direct contact between hot and cold electrical systems, which results in hot and cold electrons flowing in opposite directions, limiting the amount of electricity the device can produce.

The researchers showed that the key to achieving higher efficiency is to use nanomaterials that allow only cold electrons to flow in order to minimize the amount of heat flowing from one material to the other. Unlike bulk materials, nanomaterials can be tuned to transmit electrons that have specific energy levels.

Today's best thermoelectric devices are only about 10 percent efficient. The researchers' design could result in thermoelectric devices with efficiencies as high as 50 percent.

Thermoelectric devices capable of 50 percent efficiency would be good candidates for powering household refrigerators. Such devices would be silent, long-lived, and less bulky than today's refrigerators.

A proof-of-concept device could be built within a year or two, according to the researchers. The materials could be ready for commercial use in five to ten years, according to the researchers. The work appeared in the March 11, 2005 issue of Physical Review Letters (Reversible Thermoelectric Materials).