Researchers discover new material to produce clean energy

University of Houston researchers discover new material to produce clean energy
Nano inclusion with coherent boundary within the matrix. Credit: University of Houston

Researchers at the University of Houston have created a new thermoelectric material, intended to generate electric power from waste heat - from a vehicle tailpipe, for example, or an industrial smokestack - with greater efficiency and higher output power than currently available materials.

The material, germanium-doped magnesium stannide, is described in the current issue of the Proceedings of the National Academy of Sciences. Zhifeng Ren, lead author of the article and M.D. Anderson Chair professor of physics at UH, said the new material has a peak of 55, with a figure of merit - a key factor to determine efficiency - of 1.4.

The new material - the chemical compound is Mg2Sn0.75Ge0.25 - is important in its own right, Ren said, and he has formed a company, called APower, to commercialize the material, along with frequent collaborator Gang Chen of the Massachusetts Institute of Technology and two former students.

But he said another key point made in the paper is the importance of looking for with a high power factor, or density, in addition to the traditional focus on a high figure of merit, or efficiency, commonly referred to as ZT.

"Everyone pursued higher ZT," he said. "That's still true. But the way everybody pursued higher ZT is by reducing thermal conductivity. We were, too. But the reduction of thermal conductivity is limited. We need to increase the power factor. If remains the same and you increase the power factor, you get higher ZT."

Thermoelectric materials produce electricity by exploiting the flow of current from a warmer area to a cooler area. In the germanium-doped magnesium stannide, the current is carried by electrons.

University of Houston researchers discover new material to produce clean energy
Temperature-dependent thermal properties and ZT values. ZT values of Bi2Te2.7Se0.3 are plotted for comparison. Credit: University of Houston

"Pursuing high ZT has been the focus of the entire thermoelectric community ..." the researchers wrote. "However, for practical applications, efficiency is not the only concern, and high output power density is as important as efficiency when the capacity of the heat source is huge (such as solar heat), or the cost of the heat source is not a big factor (such as from automobiles, steel industry, etc.)"

Germanium-doped magnesium stannide has a fairly standard figure of merit, at 1.4, but a high power factor, at 55, the researchers report. That, coupled with a raw material cost of about $190 per kilogram, according to the U.S. Geological Survey Data Series, makes it commercially viable, they said.

Ren, who also is a principal investigator at the Texas Center for Superconductivity at UH, said several competing materials have lower power factors and also more expensive raw materials.

The material was created through mechanical ball milling and direct current-induced hot pressing. It can be used with waste-heat applications and concentrated solar energy conversion at temperatures up to 300 degrees Centigrade, or about 572 degrees Fahrenheit, Ren said. He said typical applications would include use in a car exhaust system to convert heat into electricity to power the car's electric system, boosting mileage, or in a cement plant, capturing waste heat from a smokestack to the plant's systems.


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Researchers find new high-efficiency thermoelectric material

More information: n-type thermoelectric material Mg2Sn0.75Ge0.25 for high power generation, PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1424388112
Citation: Researchers discover new material to produce clean energy (2015, March 3) retrieved 15 July 2019 from https://phys.org/news/2015-03-material-energy.html
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Mar 03, 2015
Another possible application is to exploit heat energy from spent nuclear waste or low yield nuclear energy sources like thorium

Mar 03, 2015
coupled with a raw material cost of about $190 per kilogram
Such a number is just an attempt for manipulation of layman public. For example the cost of gold raw material is few cents per kilogram, because it's common rock - yet the price of gold remains pretty high. Currently the price of germanium is about $2000/kg and the content of germanium inside of material described above is still rather high according to formula Ge0.25, about 25% of weight. The thermoelectric materials aren't source of clean energy as such, but in connection with cold fusion they could work so.

Mar 03, 2015
It can move away from tail pipe once it reaches 300° C

Mar 04, 2015
Would it really hurt them to quantify their good old fashioned thermoelectric efficiency percentage? The wording of this article seems to justify avoiding thermoelectric efficiency in order to defend a material with fewer applications.

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