Researchers create material to more efficiently harness waste heat

Thermoelectric materials offer the potential to harness electricity from otherwise wasted heat. Continuing research in the field could yield applications scavenging energy from vehicle exhaust systems, industrial processes and equipment, and even sunlight. Now researchers have created a material with a higher energy conversion efficiency that could make such systems more feasible.

Researchers at Northwestern University created the new material by dispersing nanocrystals of rock salt (SrTe) into lead telluride (PbTe). While this kind of nanoscale inclusion in bulk material had previously been shown to improve the energy conversion efficiency of lead telluride, it also increased the scattering of electrons, which reduced the material’s overall conductivity. The Northwestern team’s study offers the first example of using nanostructures in lead telluride to reduce electron scattering and increase the energy conversion efficiency of the material. The researchers say the resultant material is expected to enable 14 percent of waste heat to electricity.

"It has been known for 100 years that semiconductors have this property that can harness electricity," said Mercouri Kanatzidis, the Charles E. and Emma H. Morrison Professor of Chemistry in The Weinberg College of Arts and Sciences. "To make this an efficient process, all you need is the right material, and we have found a recipe or system to make this material."

Vinayak Dravid, professor of materials science and engineering at Northwestern's McCormick School of Engineering and Applied Science adds, “we can put this material inside of an inexpensive device with a few electrical wires and attach it to something like a light bulb. The device can make the light bulb more efficient by taking the heat it generates and converting part of the heat, 10 to 15 percent, into a more useful energy like electricity."

Kanatzidis says any industry that uses heat to make products, such as the automotive, chemical, brick and glass industries, could use the material to make their system more efficient. But maybe the researchers aren’t thinking big enough. An estimated 90 percent of the world’s electricity is generated by heat energy that typically operates at 30 to 40 percent efficiency, losing roughly 15 terawatts of power in the form of heat to the environment. Harnessing 10 to 15 percent of this currently wasted heat energy would translate to a substantial amount of electricity.

The results of the Northwestern University team’s study are published in the journal Nature Chemistry.