Synthesis, Electrophoretic Deposition, and Characterization of Nanostructured Thermoelectric Materials

Abstract: The world’s increasing demand for energy and supplying this energy dominantlyfrom fossil fuels has a major impact on global climate change. Theenergy crisis has gotten more alarming in the recent years which increasedthe motivation for replacing fossil fuels with greener routes for energy harvest.There are various technologies developed for harvesting energy, andthe ability to recover energy from waste heat at a wide range of temperatures (from room temperature to more than 1000 ∘C) distinguished thethermoelectric (TE) materials from the rest. The drawback about the thermoelectricdevices is that they are too inefficient to be cost-effective in manyapplications, and the developments in nanotechnology is providing somesolutions to increase the efficiency of these materials and devices.The field of thermoelectrics suffer from large discrepancy of theresults in the literature, which is generally attributed to the variations inthe materials qualities, urging a need for the development of synthetictechniques that can lead to large-scale TE materials in reasonable timeframe. In this thesis, three different routes for rapid, scalable, and energyefficient, wet-chemical synthetic techniques for bismuth chalcogenidecompounds are presented. Microwave assisted heating during reactionprovided better control over the particle properties while reducing thereaction time and carbon footprint of the synthetic method, leading tomaterials bismuth chalcogenides with promising TE transport propertiesin a scalable and reproducible manner.Hybrid TE materials, and recently emerging solid-liquid TE materialsconcept, requires fabrication of porous TE films, to study the effect of variousinterfaces, including solid and liquid electrolytes. For this purpose, wedeveloped and optimized the electrophoretic deposition (EPD) process toprepare nanostructured porous TE films by preserving the size and morphologyof the as-synthesized bismuth chalcogenide particles. A new glass based substrate is designed and fabricated to study the electronic transportproperties of the electrically active films prepared via EPD. Using this platform,we could clearly demonstrate the significance of the synthetic methodon the surface chemistry and resultant transport properties of the TE materials.The methods and materials developed in this thesis are expected toimpact and expedite further developments in the field of thermoelectrics.