Boost for material that turns waste heat into electricity

Thermoelectric device could be attached to car exhaust to recycle wasted heat to power engine
Alok Jha Green technology correspondent
guardian.co.uk,
Monday October 13 2008 16.26 BST

A material that promises to turn heat into electricity more efficiently than anything possible today has been developed by scientists. The discovery could be used to turn the waste heat from a variety of sources, such as a car's exhaust pipe or a power station, into useful power.
The technology, known as thermoelectrics, is already used today but is restricted to niche refrigeration and cooling devices. This is because of the cost of the materials and their relatively low efficiency, usually converting only 5% of the heat input into electricity.
In the new research, scientists found that adding antimony and lead to a well-known semiconductor, lead telluride, produced a highly efficient thermoelectric material that worked even at relatively high temperatures.
Mercouri Kanatzidis, a professor of chemistry at Northwestern University in Illinois who led the research, said that his new material could be used to produce a new generation of devices that were up to 14% efficient. He said a longer-term efficiency goal for his work was around 20%.
"We cannot explain [the effect] 100%, but it gives us a new mechanism, and probably new science, to focus on as we try to raise the efficiency of thermoelectrics," Kanatzidis said of his research, which is published in the latest online edition of the international chemistry journal Angewandte Chemie.
Thermoelectric materials convert heat into electricity by exploiting the difference in temperature across the different sides of a device. Electrons move from the hotter side of the material to the colder side, creating a voltage.
The potential applications are wide. A device made from thermoelectric material could, for example, be attached to a car's exaust pipe, said Kanatzidis. The side in contact with the hot exhaust would push electrons to the colder side of the thermoelectric device, which would be exposed to the air. The electricity generated could be sent back to the engine to help drive the car or charge a battery.
Since the majority of the energy in vehicle fuel is wasted as heat after being burned in an internal combustion engine, even clawing some of this back into useful power would be useful. The researchers say it could be possible to raise the reduce fuel consumption by up to 10% using an appropriate thermoelectric device. Other researchers are using steam to harness waste heat from engines.
Elizabeth Milsom, environment and energy policy manager at the Royal Society of Chemistry, pointed out its potential uses in large-scale applications. "You've got combined heat and power stations and that's good if the community lives close by, but you could have a nuclear power station that is far away from communities — if you could turn that waste heat into more electricity, that will be a good thing."
She added that because research into thermoelectrics was a relatively new area, there would still be many applications yet to be discovered. "The question is whether the materials will be available for that to happen on a commercially viable scale."