STTR Phase I: Fabrication of Low-Cost and High-Efficiency Thermoelectric Materials

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). This Small Business Technology Transfer Phase I project aims at establishing the feasibility of fabricating high-efficiency nanostructured thermoelectric at low cost. CoSb3 skutterudite nanowires will be grown by electrochemical deposition using template synthesis. After template removal, a novel controlled surface modification step will be applied to nanowires. We expect this particular surface treatment alone to reduce thermal conductivity of nanostructured CoSb3 to a greater degree compared to electrical conductivity due to differences in their respective scattering lengths. Nanostructured CoSb3 skutterudite will be grown, doped and treated under various fabrication conditions, and then characterized. Research will lead to tailored thermoelectric properties of the nanowire arrays. We will address some of these challenges regarding both size and surface modification. Complex nanoscale characterization will be performed using electrochemical techniques, X-ray diffraction, electron microscopy (SEM, TEM, EDS and EELS), and X-ray photoelectron spectroscopy (XPS). Measurements of electrical conductivity, thermal conductivity and Seebeck coefficient will be performed to study the efficiency of these nanostructures as a function of wire size, chemical composition and surface roughness in order to obtain an optimal condition for the highest efficiency. This technology lays the foundation for large-scale fabrication of high efficiency thermoelectric devices for energy conversion. The unique combination of electrochemical deposition and surface roughening has great potential for mass production of low-cost and high-efficiency thermoelectric materials that can not be achieved by bulk processing techniques. Skutterudite group (e. g., CoSb3) thermoelectric materials are used to generate electrical power from different heat sources (e. g., stove top generators, engine exhaust powered alternator replacement, self-powered appliances), but the current market is limited by a low efficiency. With an increased ZT, CoSb3 processed by this technology can be used in many power conversion devices operating at intermediate temperatures; moreover, it may compete with Bi2Te3 for low temperature applications. Additionally, this technology will enhance the scientific and technological understanding of nanostructured thermoelectric materials. To date, most of the work on electrodeposited thermoelectric thin films and nanostructures focuses on synthesis, primarily investigating compositions and structure. A dissonant gap between synthesis and characterization of the thermoelectric properties, namely the Seebeck coefficient and thermoelectric figure of merit, creates only a partial picture for published works. While composition and structure of electrodeposits are crucial indicators of physical properties, their measured thermoelectric performance will ultimately dictate their usefulness in heating, ventilation, and/or air conditioning (HVAC) in to vehicles and solar thermal industry.