Nanostructured thermoelectric materials based on solution phase synthesis: Towards efficiency and sustainability

Haoran Yang, Purdue University

Abstract

Thermoelectric devices fulfill the direct conversion between heat and electricity, which have many potential applications including waste heat harvest, solar thermoelectric power generation, solid state cooling, and etc. However, it is a challenge to develop materials with superior performance that allow the practical uses of thermoelectric technology. Recent progresses in nanostructured thermoelectric materials have shown great potential in the enhancement of thermoelectric figure of merit ZT. Meanwhile, it is equally important to consider the sustainability issues of the thermoelectric technology, which should satisfy many features such as low-cost, energy-efficient, scalable, and pollution-free. In the present study, we aim at both the efficiency and sustainability in the development of nanostructured thermoelectric materials. We explore the feasibility of using solution phase synthesized nanostructures as the building blocks for the fabrication of high-performance thermoelectric materials, and then extend our research on some of the sustainability issues. Firstly, we show that composition modulation can be used to control the doping level in Ag2Te nanowires, which yield nano-grained samples with enhanced ZT. Secondly, we demonstrate that a novel kind of dumbbell PbTe-Ag 2Te heterostructures can be synthesized with wet chemistry, and a complex nano-inclusion-in-matrix structure can be achieved correspondingly, which mimics similar structures fabricated by melt synthesis that have been proven to be successful, and gives rise to a further enhancement in ZT. Thirdly, we study the possibility to replace the hazardous chemical hydrazine with a green chemical ascorbic acid in the synthesis, and we show that various metal telluride nanowires can be synthesized including Ag2Te, Bi 2Te3 and etc. Finally, efforts have been made seeking for novel thermoelectric materials contain only non-toxic and earth-abundant elements, and as a proof-of-concept study, Cu2ZnSnS4 nanocrystals based thermoelectric properties are investigated. The results suggest the bottom up approach toward nanostructured thermoelectric materials based on solution phase synthesis is of great potential. Not only simple nano-grained materials but also some more complex heterogeneous structures can be achieved with this approach. With proper control over the composition, these samples exhibit enhanced ZT. Moreover, the complex structures also provide an ideal platform to study the newly proposed energy filtering effect, which could enhance the thermoelectric power factor. The study on the sustainability has made progressed on "greener" chemistry for the synthesis of nanostructured thermoelectric materials. The searching for novel thermoelectric materials with environmental benign composition and cheap elements, although is still in the preliminary stage, stands for the future direction.

Degree

Ph.D.

Advisors

Wu, Purdue University.

Subject Area

Chemical engineering|Nanotechnology|Materials science

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