Purified tin selenide has extraordinarily high thermoelectric performance
Perseverance, NASA’s 2020 Mars rover, is powered by something very desirable here on Earth: a thermoelectric device, which converts heat to useful electricity.
On Mars, the heat source is the radioactive decay of plutonium, and the device’s conversion efficiency is 4-5%. That’s good enough to power Perseverance and its operations but not quite good enough for applications on Earth.
A team of scientists from Northwestern University and Seoul National University in Korea now has demonstrated a high-performing thermoelectric material in a practical form that can be used in device development. The material — purified tin selenide in polycrystalline form — outperforms the single-crystal form in converting heat to electricity, making it the most efficient thermoelectric system on record. The researchers were able to achieve the high conversion rate after identifying and removing an oxidation problem that had degraded performance in earlier studies.
The polycrystalline tin selenide could be developed for use in solid-state thermoelectric devices in a variety of industries, with potentially enormous energy savings. A key application target is capturing industrial waste heat — such as from power plants, the automobile industry and glass- and brick-making factories — and converting it to electricity. More than 65% of the energy produced globally from fossil fuels is lost as waste heat.
“Thermoelectric devices are in use, but only in niche applications, such as in the Mars rover,” said Northwestern’s Mercouri Kanatzidis, a chemist who specializes in the design of new materials. “These devices have not caught on like solar cells, and there are significant challenges to making good ones. We are focusing on developing a material that would be low cost and high performance and propel thermoelectric devices into more widespread application.”
Kanatzidis, the Charles E. and Emma H. Morrison Professor of Chemistry in the Weinberg College of Arts and Sciences, is a co-corresponding author of the study. He has a joint appointment with Argonne National Laboratory.
Details of the thermoelectric material and its record-high performance was published Aug. 2 in the journal Nature Materials.
In Chung of Seoul National University is the paper’s other co-corresponding author Vinayak Dravid, the Abraham Harris Professor of Materials Science and Engineering at Northwestern’s McCormick School of Engineering, is one of the study’s senior authors. Dravid is a long-time collaborator of Kanatzidis’.
Thermoelectric devices are already well defined, says Kanatzidis, but what makes them work well or not is the thermoelectric material inside. One side of the device is hot and the other side cold. The thermoelectric material lies in the middle. Heat flows through the material, and some of the heat is converted to electricity, which leaves the device via wires.
The material needs to have extremely low thermal conductivity while still retaining good electrical conductivity to be efficient at waste heat conversion. And because the heat source could be as high as 400-500 degrees Celsius, the material needs to be stable at very high temperatures. These challenges and others make thermoelectric devices more difficult to produce than solar cells.
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