Washington, Oct 10 : A Northwestern University-led research team has identified a promising new material that could efficiently convert waste heat into electricity to help power cars and improve gas mileage.
The researchers discovered that adding two metals, antimony and lead, to the well-known semiconductor lead-telluride, produces a thermoelectric material that is more efficient at high temperatures than existing materials.
"We cannot explain this 100 percent, but it gives us a new mechanism - and probably new science - to focus on as we try to raise the efficiency of thermoelectrics," said Mercouri G. Kanatzidis, Charles E. and Emma H. Morrison Professor of Chemistry in the Weinberg College of Arts and Sciences.
Current thermoelectric technology is only used in niche markets, such as solid-state refrigeration and cooling, because the materials are not very efficient.
With new materials and increased efficiency, devices based on thermoelectrics could find widespread use in the automotive industry, solar energy conversion and the conversion of waste heat from nuclear reactors, smokestacks and industrial equipment.
"It's a big accomplishment to recover some of the heat or energy that would otherwise be lost and convert it into useful energy," said Kanatzidis. "That's what thermoelectrics can do, but we need to make them more efficient to really be practical," he added.
Thermoelectric materials are only 5 to 6 percent efficient today, but a new generation of materials based on recent discoveries including this one at Northwestern, could produce devices with 11 to 14 percent efficiency, says Kanatzidis.
The long-term goal is to reach 20 percent.
Thermoelectric materials convert heat into electricity by taking advantage of temperature differences.
Electrons move from the hot end of the material to the cold end, creating positive and negative electrodes and an electrical voltage.
A thermoelectric device, for example, could be attached to a car's tailpipe. The side of the material in contact with the tailpipe would be the hot side, and the side exposed to the air would be the cold side.
The temperature difference would be enough to generate electricity, which would be returned to the car's engine for additional torque.
Such devices also could be used in large industrial plants, such as those for power, chemical production and glass making.
Car companies are working on the thermoelectrics problem as part of their strategy to raise the overall gas mileage of vehicles, according to Kanatzidis.
Researchers hope to raise mileage by 5 to 10 percent per gallon using thermoelectrics, which would be significant.