AsianScientist (Jan. 4, 2018) – A team of researchers at Osaka University in Japan have devised a method to generate electricity from heat at room temperature. They published their findings in the journal Rapid Research Letters.
Thermoelectric (TE) materials display the thermoelectric effect: apply heat on one side, and an electric current starts to flow. Conversely, run an external current through the device, and a temperature gradient forms, that is, one side becomes hotter than the other. By interconverting heat and electricity, TE materials can be used as either power generators (given a heat source) or refrigerators (given a power supply).
TE materials could play a key role in future technologies. Although the applications of these remarkable compounds have long been explored, they are mostly limited to high-temperature devices.
In this study, researchers at Osaka University, Japan, in collaboration with Hitachi Ltd., developed a TE material with an improved power factor at room temperature. The power factor is proportional to both electrical conductivity and a term called the Seebeck coefficient, which is a measure of the magnitude of an induced charge in response to a temperature difference across a material.
“Unfortunately, most TE materials are often based on rare or toxic elements. To address this, we combined silicon, which is common in TE materials, with ytterbium, to create ytterbium silicide [YbSi2],” said study co-author Dr. Sora-at Tanusilp of Osaka University. “We chose ytterbium over other metals for several reasons. First, its compounds are good electrical conductors. Second, YbSi2 is non-toxic. Moreover, this compound has a specific property called valence fluctuation that makes it a good TE material at low temperatures.”
The researchers also demonstrated that YbSi2 has an unusual layered structure. While the ytterbium atoms occupy crystal planes similar to that of their pure metal state, the silicon atoms form hexagonal sheets between those planes, resembling the carbon sheets in graphite. This blocks the conduction of heat through the material, and therefore keeps the thermal conductivity down, preserving the temperature gradient.
The researchers believe that heat conduction is further suppressed due to traces of impurities within the material, and other defects. Nonetheless, YbSi2 displayed an encouragingly high power factor of 2.2 mWm-1K-2 at room temperature.
“The use of ytterbium shows we can reconcile the conflicting needs of TE materials through carefully selecting the right metals. Room-temperature TEs, with moderate power, can be seen as complementary to the conventional high-temperature, high-power devices. This could help unlock the benefits of TE in everyday technology,” said Associate Professor Ken Kurosaki of Osaka University, who is the corresponding author of the study.
The article can be found at: Tanusilp et al. (2017) Ytterbium Silicide (YbSi2): A Promising Thermoelectric Material with a High Power Factor at Room Temperature.
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Source: Osaka University; Photo: Swatchith (Own work) [CC BY 4.0]/Wikimedia Commons.
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