High-efficiency, Cost-effective Thermoelectric Materials/Devices for Industrial Process Refrigeration and Waste Heat Recovery
Funded by U.S. Department of Energy
Project Summary
This is the final report of DoE STTR Phase II project, “High-efficiency, Cost-effective Thermoelectric Materials/Devices for Industrial Process Refrigeration and Waste Heat Recovery”. The objective of this STTR project is to develop a cost-effective processing approach to produce bulk high-performance thermoelectric (TE) nanocomposites, which will enable the development of high-power, high-power-density TE modulus for waste heat recovery and industrial refrigeration. The use of this nanocomposite into TE modules are expected to bring about significant technical benefits in TE systems (e.g. enhanced energy efficiency, smaller sizes and light weight). The successful development and applications of such nanocomposite and the resultant TE modules can lead to reducing energy consumption and environmental impacts, and creating new economic development opportunities.
In this report project, we have selected two nanocomposite TE materials, PbTe-PbSe and Bi2Te3-Sb2Te3 as model material systems. The major reasons of selecting PbTe-based nanocomposites are: (1) PbTe and its composites are good bulk TE materials; and (2) Superlattice PbTe/PbSe had ZT>3 [Harman et al, Science 297-2229 (2002)] and PbTe-PbSe nanocomposites are thus very promising in achieving high ZT value. Recent development efforts also support the feasibility of our research, which include: (1) 100 nm PbTe nano-crystals synthesized [Ji et al, J. Electr. Mater. 36-721 (2007)]; and (2) Dispersion of Sb nanoparticles into PbTe results in the decrease in thermal conductivity, resulting in the increase in ZT [Sootsman et al, Chem. Mater. 18-4993(2006)]. The reasons for choosing Bi2Te3-based material system are: (1) Bi2Te3– Sb2Te3 is most widely used thermoelectric material; and (2) our processing procedures have a promising potential to further improve the performance of Bi2Te3– Sb2Se3 material system.
Although great potentials have been demonstrated with some promising results, more studies for processing this class of nanocomposites are anticipated before their full potentials can be realized. The most challenging issue is the methods currently employed are not suitable for mass production, and are unable to produce large-dimension materials which are essential to achieve high power output in TE modules. The potential solution to address this issue is to develop a cost-effective approach that is able to efficiently synthesize high-performance TE nanocomposites in both large quantities and large dimensions.
In the previous Phase I accomplished, we has successfully carried out the feasibility study of a cost-effective scalable process with the potential to fulfill the above stated expectation, in which highly-oriented PbSe (or Bi2Te3)-nanowires (quantum-confined materials) are introduced into a PbTe (or Bi2Se3) bulk nanocrystalline material to form a high-efficiency thermoelectric nanocomposite.
The focus in this Phase II is on the process development and optimization for the production of high-ZT TE nanocomposites based on PbTe-PbSe and Bi2Te3-Bi2Se3 material systems. The research activities include material processing development and characterization. The processing approach includes: (1) synthesis of nanowires or nanocrystals, (2) High-energy ball milling submicro/nano-sized powders, and (3) consolidation of composite powder mixtures into large-dimension bulk materials. In addition, we also carried out the development of TE module fabrication and the associated waste heat recovery system.