Colloidal Nanocrystal Routes to Inorganic Nanocomposite Thermoelectric Materials

Arizona State University, Scottsdale AZ

Investigators

Abstract

Non-technical Abstract With the support of the Solid State and Materials Chemistry program in the Division of Materials Research, this project synthesizes and characterizes advanced nanocomposite thermoelectric materials. Thermoelectric materials directly convert temperature differences into voltage differences and vice versa. This phenomenon enables the creation of solid-state thermoelectric power generators and coolers that can play a promising role in addressing the energy landscape and climate change. One of the most promising applications of thermoelectric devices is the conversion of waste heat (e.g. automotive exhaust) into electricity. Thermoelectric coolers are also promising because these devices do not use refrigerants, which are generally potent greenhouse gases. As a part of this activity, the principal investigator is creating a thermoelectric lab module for an undergraduate course on internal combustion engines. This lab integrates thermoelectric devices into an engine's exhaust system, and thereby enables the study of waste heat conversion into electricity. The engine is also equipped with a dynamometer that characterizes its mechanical power. Hence students are able to measure the electric power produced by the thermoelectric devices as they relate to the primary engine variables: speed and torque. Technical Abstract The goal of this project is to advance the thermoelectric materials field by combining three separate mechanisms to improve performance in nanocomposite materials. First, the microstructure of these composites consists of nanoparticles embedded in a matrix. This morphology promotes strong phonon scattering and favorable reductions in thermal conductivity. Second, quantum-confined nanocrystals are being used for the nanoparticle inclusions. This confinement causes sharp peaks in the electronic density of states, which leads to large thermoelectric power factors. Lastly, band convergence is being used to create a large effective band degeneracy, which further promotes large thermoelectric power factors. Colloidal nanocrystals and metal-chalcogenide cluster precursors are being combined as modular building blocks to create the nanocomposites. The local atomic and electronic structures of the nanocomposites are being characterized using an aberration-corrected scanning transmission electron microscope equipped with a high resolution electron energy loss spectrometer. A complete suite of thermoelectric property measurements (i.e. Seebeck coefficient, electrical conductivity, and thermal conductivity) is being performed on the nanocomposites over a broad range of temperatures. Collectively, this project's combination of novel nanocomposite formation, atomistic materials characterization, and thermoelectric measurement suite enables the targeted discovery of thermoelectric design rules for improved performance.