Northwestern University
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Pure tin selenide has a very high thermoelectric performance.
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Nationalgeographic.co.id—A team of scientists from Northwestern University and Seoul National University succeeded in developing the material thermoelectric high-performance that can change waste heat into electrical energy. Details of the findings have been published in the Journal Nature Material on August 2, 2021.
Researchers have demonstrated a high-performance thermoelectric material in a practical form that can be used in device development. The material is pure tin selenide in polycrystalline form. This form outperforms single-crystal forms in converting heat into electricity, making it the most efficient thermoelectric system ever recorded to date.
Thermoelectric devices are already in use today, but only in special applications such as those used Mars Curiosity Rover or Mars explorer. On the Red Planet the heat source is the radioactive decay of plutonium, and the device’s conversion efficiency reaches 4-5 percent. That’s good enough to support operations on Mars, but not good enough for applications on Earth.
“Thermoelectric devices have been used (today), but only in special applications, such as in the Mars rover,” said Mercouri Kanatzidis in a Northwestern University release.
Kanatzidis, a chemist who specializes in the design of new materials, explains that the researchers were able to achieve high conversion rates after identifying and eliminating oxidation problems that had degraded performance. The main application target of thermoelectric devices is to capture industrial waste heat, with enormous energy saving potential.
Polycrystalline tin selenides can be developed for use in solid-state thermoelectric devices in various industries. Huge energy saving potential. The main application target is to capture industrial waste heat—such as from power plants, the automobile industry and glass and brick manufacturing plants—and then convert it into electricity.
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NASA
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The Mars Curiosity Rover uses a thermoelectric device to operate.
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So far, more than 65 percent of the energy generated globally from fossil fuels is lost as waste heat. “These devices haven’t caught on like solar cells, and there are significant challenges to making them better. We are focused on developing materials that will be low-cost and high-performance that will propel thermoelectric devices into a wider range of applications,” said Kanatzidis.
Kanadzidis said that current thermoelectric devices are well defined. However, the thing that makes it work well or not is the thermoelectric material inside. One side of the device is hot and the other side is cold, while the thermoelectric material is located in the middle. Heat flows through the material, while some of the heat is converted into electricity.
According to him, the material must have a very low thermal conductivity while maintaining good electrical conductivity to be efficient when converting waste heat. And because the heat source can reach 400-500 degrees Celsius, the material must be stable at very high temperatures.
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“This challenge makes thermoelectric devices more difficult to manufacture than solar cells,” he said.
Previously, in 2014, Kanatzidis and his team had reported the discovery of a surprising material that is the best in the world for converting waste heat into useful electricity, namely the crystalline form of the chemical compound tin selenide.
However, despite the important findings, the single-crystal form is impractical for mass production. That’s because of its brittleness and tendency to peel.
According to the researchers, tin selenide in polycrystalline form, which is stronger and can be cut and shaped for applications, is urgently needed. So the researchers turned to studying the material in that form. Unpleasant surprise, they found the material’s high thermal conductivity, unlike in its single-crystal form.
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VanderWolf-Images
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More than 65% of the energy generated globally from fossil fuels is lost as waste heat
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“The expectation was that tin selenide in polycrystalline form would not have a high thermal conductivity, but it does. We have a problem,” Kanatzidis said.
However, upon further examination, the researchers found that the tin shell was oxidized in the material. Heat flows through the conductive skin, increasing the thermal conductivity, which is undesirable in thermoelectric devices.
After knowing that, that oxidation comes from the process itself and the starting material. The research team found a way to remove oxygen. The researchers were able to produce lead selenide material without oxygen.
“This (will) open the door for new devices to be made from polycrystalline tin selenide materials and their wider applications,” said Kanatzidis.
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