Abstract
We demonstrate filled CoSb3 skutterudite materials with excellent thermoelectric (TE) performance that results in one of the highest reported single stage module efficiency. The improvement in TE material performance was obtained by creating isotype n/n “bulk heterojunction” structure through assembly of novel skutterudite nanocrystals with different Yb-doping content. Combination of significant increase in carrier transport through heterojunction structure and reduction in long-range acoustic phonon transmission by two-phase mixture resulted in enhanced power factor and reduced lattice thermal conductivity. As a result, the figure-of-merit (zT) of heterojunction TE material is improved by more than 35% compared with pristine single homogeneous material. Using these improved TE materials, a high module conversion efficiency of ~9.15% was obtained when operating between 650 °C and 50 °C. This is one of the highest conversion efficiency among the practically measured single stage modules.
| Original language | English (US) |
|---|---|
| Article number | 104193 |
| Journal | Nano Energy |
| Volume | 66 |
| DOIs | |
| State | Published - Dec 2019 |
Funding
Fig. 1a shows the EDS spectra taken from two representative locations in the A0.5B0.5 sample with nano grains (Fig. 1a). The inset high angle annular dark field (HAADF) STEM image reveals the Z-contrast across the characterized area, where brighter contrast represents higher average atomic number. In the EDS spectra, the Yb peaks with clear higher intensity were observed on bright grain in HAADF image indicating higher Yb content compared to that on dark grain, which is further confirmed by quantitative EDS result. A composition gradient can be observed in different grains originating from particle A and B, and a three-dimensional network comprising of grains A or B in composite A0.5B0.5 were formed as n/n BHJ configuration due to the different band gaps of composition A and B, as shown in Fig. 1d and e. The EDS mapping results obtained from STEM and SEM (Fig. 1b and c) also illustrate the Yb-compositional gradient between nano grains due to the BHJ structure. In order to further verify the existence of phase separation, samples with composition 50 vol% Ca0.2Co4Sb12 + 50 vol% Yb0.3Co4Sb12 were prepared using same procedure. The Yb0.3Co4Sb12-based and Ca0.2Co4Sb12-based grains are defined as Yb-rich and Yb-deficient grains. The backscattered electron (BSE) images, Yb elemental mapping and EDS spectra are displayed in supporting information (SI), Fig. S2. Due to the significant mass difference between Ca and Yb, the contrast between Yb-rich and Yb-deficient phase is explicit in the microstructure. The white dash lines and red dot lines were selectively marked to guide the visualization of Yb-rich grain (bright grain) and Yb-deficient grain (dark grain), respectively. The EDS spectrum taken from the bright grain has significantly higher intensity for the Yb M and Yb L peaks compared to that obtained from the dark grain, indicating that Yb is well retained in one phase rather than diffuse into the Yb-deficient grain after annealing, which is consistent with the heterogeneous A0.5B0.5 case.This work was supported by the “TherMAT” research program, Future Pioneering Projects/Research and Development of Thermal Management Materials and Technology, commissioned by New Energy and Industrial Technology Development Organization and Japanese Ministry of Economy, Trade and Industry. W. L. and S. P. would like to acknowledge the financial support from the DARPA MATRIX program. G. N. was supported through the NSF-CREST Grant number HRD 1547771. This work also supported by the U.S. Department of Energy, Office of Science and Office of Basic Energy Sciences under award number DE-SC0014520 (MGK, XZ&VPD, EBI&CW for physical, electron microscopy, and computational investigations). Shashank Priya is currently Professor of Materials Science and Engineering at Penn State University. He is also serving as Associate Vice President for Research and Director of Strategic Initiatives in the Office of the Vice President for Research (OVPR). His research is focused in the areas related to multifunctional materials, energy and bio-inspired systems. He has published over 400 peer-reviewed high impact journal papers and more than 60 conference proceedings covering these topics. Additionally, he has published more than ten book chapters, ten US patents, and ten edited books. His research group is funded by DARPA, AFOSR, ARO, NSF, DOE, ONR and several industries. The research group is very interdisciplinary, consisting of materials scientists, physicists, mechanical engineers, robotics, and electrical engineers. This allows the group to conduct integrated research addressing several aspects at the material, component, and system level. He is the founder and chair of the Annual Energy Harvesting Society Meeting. He is also serving as the member of the Honorary Chair Committee for the International Workshop on Piezoelectric Materials and Applications (IWPMA). This work was supported by the “ TherMAT ” research program, Future Pioneering Projects/ Research and Development of Thermal Management Materials and Technology , commissioned by New Energy and Industrial Technology Development Organization and Japanese Ministry of Economy, Trade and Industry . W. L. and S. P. would like to acknowledge the financial support from the DARPA MATRIX program. G. N. was supported through the NSF- CREST Grant number HRD 1547771 . This work also supported by the U.S. Department of Energy , Office of Science and Office of Basic Energy Sciences under award number DE-SC0014520 (MGK, XZ&VPD, EBI&CW for physical, electron microscopy, and computational investigations). Eric B. Isaacs received his PhD in Applied Physics from Columbia University in 2016, supported by the US Department of Energy Computational Science Graduate Fellowship. His topic of study was the electronic structure and phase stability of materials with strong electronic correlations, such as rechargeable battery cathodes. He is currently a postdoctoral fellow at Northwestern University, applying first-principles calculations and data-driven tools to the discovery and characterization of thermoelectric materials.
Keywords
- Bulk heterojunction
- Conversion efficiency
- Nano grain engineering
- Skutterudite
- Thermoelectric
ASJC Scopus subject areas
- Renewable Energy, Sustainability and the Environment
- General Materials Science
- Electrical and Electronic Engineering
