Abstract
Energy filtering has been a long-sought strategy to enhance a thermoelectric material's figure of merit zT through improving its power factor. Here we show a composite of multi-layer graphene nanoplatelets (GNP) and n-type Mg3Sb2 leads to the expression of an energy filtering like effect demonstrated by an increase in the material's Seebeck coefficient and maximum power factor, without impact on the material's carrier concentration. We analyse these findings from the perspective of a heterogeneous material consisting of grain and grain boundary phases, instead of a more traditional and common analysis that assumes a homogeneously transporting medium. An important implication of this treatment is that it leads to the development of an interfacial Seebeck coefficient term, which can explain the observed increase in the material's Seebeck coefficient. The contribution of this interfacial Seebeck coefficient to the overall Seebeck coefficient is determined by the relative temperature drop across the grain boundary region compared to that of the bulk material. In Te doped Mg3Sb2 we show the introduction of GNP increases the interfacial thermal resistance of grain boundaries, enhancing the contribution of the interfacial Seebeck coefficient arising from grain boundaries to the overall Seebeck coefficient. Without significant detriment to the electrical conductivity this effect results in a net increase in maximum power factor. This increased interfacial thermal resistance also leads to the synergistic reduction of the total thermal conductivity. As a result, we enhance zT of the Mg3Sb2 to a peak value of 1.7 near 750 K. Considering the two-dimensional nature of the grain boundary interface, this grain boundary engineering strategy could be applied to a few thermoelectric systems utilizing various two-dimensional nanomaterials.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 4114-4121 |
| Number of pages | 8 |
| Journal | Energy and Environmental Science |
| Volume | 13 |
| Issue number | 11 |
| DOIs | |
| State | Published - Nov 2020 |
Funding
The authors acknowledge support from the NASA Science Mission Directorate’s Radioisotope Power Systems Thermoelectric Technology Development program. This work was performed under the following financial assistance award 70NANB19H005 from U.S. Department of Commerce, National Institute of Standards and Technology as part of the Center for Hierarchical Materials Design (CHiMaD). Y. L. acknowledges the Marie Skłodowska-Curie individual Fellowship (No. 800031) provided by the European Union’s Horizon 2020 research and innovation programme. D. L. and M. C. H. acknowledge the Department of Energy (Grant DE-SC0019356) for support of the GNP processing work. N. M. appreciates the Swedish Research Council for the International PostDoc grant and the research funds provided by Helge Ax:son Johnsons stiftelse, the Barbro Osher Foundation and the Royal Swedish Academy of Engineering Sciences. M. G. K and T. J. S thank the Department of Energy, Office of Science Basic Energy Sciences grant DE-SC0014520 for support. Measurement was made use of the EPIC facility of Northwestern University’s NUANCE Centre and the IMSERC X-ray Facility at Northwestern University, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205) and the MRSEC program (NSF DMR-1720139); the State of Illinois and International Institute for Nanotechnology (IIN). The authors acknowledge use of facilities within the Monash Centre for Electron Microscopy (MCEM). The authors thank Maxwell Thomas Dylla, Ian Witting, Riley Hanus, and Stephen Dongmin Kang for fruitful discussions about the modelling work.
ASJC Scopus subject areas
- Environmental Chemistry
- Renewable Energy, Sustainability and the Environment
- Nuclear Energy and Engineering
- Pollution