Green Nano The Nano–Material that can Produce Clean Energy from Waste Heat

Author / Editor: Jeannie Kever * / Sebastian Gerstl

Researchers at the University of Houston have created a new thermoelectric material, intended to generate electric power from waste heat with higher output power than currently available materials.

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Image 2: Chart showing temperature-dependent thermal properties and ZT values.
Image 2: Chart showing temperature-dependent thermal properties and ZT values.
(Source: University of Houston)

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 power factor of 55, with a figure of merit – a key factor to determine efficiency – of 1.4.

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

Increasing the Power factor

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

"The way everybody pursued higher ZT is by reducing thermal conductivity," Ren said. "We were, too. But the reduction of thermal conductivity is limited. We need to increase the power factor. If thermal conductivity 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.

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