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NEXTEC (2011-2014)

NEXTEC project description

The project NEXTEC (Next Generation Nano Engineering Thermoelectric Converters) has been June 2011 to May 2014.


TRL at project start: 2 (Technology Concept Formulated)

TRL at project end: 4 (Technology validated at Lab)

NEXTEC Project objectives

1) Definition of system requirements

An important objective was to identify the most promising industrial applications of novel nano-structured TE and hence deduce the implications for the materials and modules to be developed during the project. This includes not just the TE properties of the novel nano-structured materials, but also other material issues relating to the design, fabrication and stability of the TE modules. Taking these into account was necessary to enable the industrial validation of the nano-structured TE materials.

2) Fabrication of novel nanostructured materials

After choosing the application scenarios, the next main objective was to fabricate novel and high-performance TE materials. We focused on development of state-of-the-art bismuth telluride system for cooling applications and the most promising SKT architecture for energy generation modules. Other novel material composition/architecture, such as nanoporous materials/metal foams were also investigated as potential TE material candidates. In this project, bulk NS TE nanocomposites were designed and developed by adding advanced low-dimensional TEs as well as immiscible ceramic oxides as additional phase to the matrix consisting of bulk NS TE materials. In this manner, the TE performance was further enhanced by the additional phases while the materials were easily processed for module/device fabrication due to their bulk-like nature. The additional phases also called “nano-inclusion”, had another function of hindering the grain growth during the high-temperature post fabrication processes such as reduction, compaction and sintering, and therefore preserved the excellent “nano-effects” of the materials. The in-depth investigation of the underlying physics was also undertaken with theoretical modeling validating our experimental findings.

3) Characterization and TE metrology development

Another important objective of NEXTEC was a reliable method for evaluation of the TE properties. Included in this, are the measurement of the Seebeck coefficient, the electrical conductivity, the thermal conductivity, the carrier concentration and the mobility of Bi2Te3- and CoSb3- based nanostructured materials as a function of the chemical composition and microstructure from 20 to 1000 K. The measurements will be performed at each fabrication steps in order to chronologically correlate the change of the transport properties as a function of the microstructure. The measurement will be performed on spark plasma sintered, screen printed and electrodeposited materials. For this, we developed a round-robin process for transport property evaluation of the developed materials. In addition, development of novel metrology instruments that enable rapid and high-throughput measurement of electrical and thermal conductivities were also carried out in this project.

4) Module fabrication

One of the main objectives of NEXTEC was to incorporate the novel SKT materials into novel TE modules, to characterize the modules and to test their performance under realistic operating conditions. In order to achieve these objectives several sub-tasks had to be addressed, as follows. Conventional planar designs and a new ring configuration for a high-temperature TE module had to be developed and optimized. The TE powder had to be sintered into suitable form and the resulting pellets fabricated into modules. Another sub-task was to establish test benches to characterize the thermal and electrical performance of modules under ideal conditions, and to assess the reliability of these test benches, including a round robin. Additional test benches had to be developed in order to assess the performance of prototype modules under realistic operating conditions. A further task was to establish system-level simulation tools, which used the measurement results to evaluate the feasibility of TE technology for the foreseen applications, e.g. generating electricity from hot car exhaust. An additional aim was to fabricate a planar module with improved Bi2Te3 and test its performance for cooling applications.

5) Life cycle impact analysis

The main objective of this work package is the evaluation of the environmental impact caused by the nanomaterials used in the fabrication of novel TE modules developed in this project. This task required, among other activities, designing a new framework for the life cycle impact assessments of nanomaterials based on the existing model ReCiPe 2008 (specifically, nanomaterials used for the fabrication of novel TE modules).