Room Temperature SiGe Thermoelectric Material for Power Generation from Waste Heat in Everyday Life

～ Bringing the Materials Used in Spacecraft Closer to You: Demonstrating a Threefold Increase in Thermoelectric Power Factor Using a Unique Methodology ～

A research group led by Professor Yoshiaki Nakamura of the Graduate School of Engineering Science, Osaka University, Professor Takeshi Fujita of the School of Environmental Science and Engineering, Kochi University of Technology, Professor Jun-ichiro Ohe of Department of Physics, Toho University, and Senior Researcher Eiichi Kobayashi of the Kyushu Synchrotron Light Research Center has proposed an innovative methodology for improving thermoelectric performance and has achieved the highest thermoelectric conversion power factor using environmentally friendly SiGe materials. The research group proposes an innovative methodology for improving the thermoelectric performance and achieved the highest thermoelectric conversion power factor (= Seebeck coefficient)^2 x (electrical conductivity)in environmentally friendly SiGe materials at room temperature (which is approximately three times higher than that of conventional SiGe). Thermoelectric materials are expected to be a new source of clean energy because they can directly convert a large amount of waste heat into electricity. However, simultaneously increasing the Seebeck coefficient and the electrical conductivity has been a longstanding issue, as a trade-off relationship exists between the two. Our research group used a suction casting method to fabricate SiGe and Au composite materials and found that adding the Au impurities to SiGe achieved a resonance level. The research group succeeded not only in increasing the Seebeck coefficient owing to the resonance level formed by adding the Au impurity to SiGe, but also in increasing the electrical conductivity at the same time by taking advantage of the high electrical conductivity of the Au crystal. As a result, we succeeded in achieving the highest thermoelectric power factor that has been reported near room temperature, which is three times higher than the value of the SiGe thermoelectric material used in the radioisotope thermoelectric generator (RTG) power supply aboard a spacecraft (Fig. 1).

Until now, SiGe materials have been used only in the high-temperature region as power sources for spacecraft. With the achievement obtained in our study, we can expect to realize a “new energy society,” in which waste heat generated by high-performance SiGe materials operating at near room temperature can be reused as electric energy.

Key Research Findings

Achieved a simultaneous increase in the electrical conductivity and Seebeck coefficient of an environmentally friendly SiGe thermoelectric material, and succeeded in simultaneously increasing the electrical conductivity and Seebeck coefficient to obtain a high thermoelectric power factor at room temperature.
In thermoelectric conversion, a large electrical conductivity and Seebeck coefficient are necessary to achieve high efficiency, but it has been difficult to simultaneously increase both physical properties because of their correlation. This has been the greatest obstacle in converting waste heat into electricity.
This work paves the way for the realization of a thermoelectric power generation source that uses unused heat as an energy source using non-toxic materials operating at room temperature.

These results have been published in Journal of Materials Chemistry A, on January 29, 2021.

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