Studies on chalcogenide type thermoelectric nanomaterials for improving their thermoelectric properties

Abstract

Researches into various renewable energies have been intensively carried out over the past several decades due to the serious exhaustion of fossil fuels and the global warming on the planet’s environment. As one of the renewable energies, thermoelectricity has grabbed much attention and has been recognized to be promising because of its recent meteoric developments for the last decade. Thermoelectricity is the generic term for the energy conversion technology between a thermal and an electric energy – one can generate electricity from an temperature difference in a thermoelectric device caused by external heat or can also obtain simultaneous cooling and heating effects by supplying electricity to the device. In this way, a thermoelectric technology is mainly classified into the two application parts, that is, thermoelectric generation and solid-state cooling, but, conventionally, it has only been employed for the special purposes such as various power supplies for spaceships or for military equipment. However, an application field of the technology has rapidly been extended with the recent developments because the technology does not damage environment and it barely costs for maintenance. In detail, one can possibly generate and convert an electric energy with no environmental problems such as toxic byproducts and noise, which inevitably appear in traditional systems. Besides, there is no wear and tear caused by mechanical friction

thus, a thermoelectric system is usually highly durable and reliable. However, researchers have currently faced with some obstacles to the commercialization of a thermoelectric technology such as low energy conversion efficiency and high costs of raw materials and device components. Nevertheless, researches into thermoelectricity are extensively ongoing because of renewed requirement for sustainable energy sources as well as significant magnitude of environmental problems. The efficiency of thermoelectric conversion is greatly affected by the performance of thermoelectric materials and the technology of fabricating thermoelectric devices. Many research groups have endeavored to improve the thermoelectric performance of their materials by developing the new-type of thermoelectric materials or by enhancing the properties of existing materials. As a result, researchers are gradually reporting the thermoelectric materials that overcome the limitations of conventional materials – researchers are designing various thermoelectric materials in terms of low costs as well as high performance at different operation temperatures, and thus economic feasibility are steadily improved for the commercialization. For these materials, a variety of applications is suggested over low- to mid-temperature operations, such as electric generation from body temperature, waste heat-to-electricity conversion in automobiles and industries, heating and cooling seats in automobiles, and refrigerant-free heating, ventilating, and air conditioning (HVAC) systems, last but not least. Among various thermoelectric materials, chalcogenide-based thermoelectric materials (i.e., Bi2Te3, Sb2Te3, BixSb2-xTe3, Bi2TeySe3-y etc.) were first developed in 1940’s and the researches into the chalcogenide-based materials are still actively ongoing because of their feasible thermoelectric properties at the low-temperature region, below 300 °C. Although the chalcogenide-based materials are known to exhibit the best thermoelectric performance at the temperature region, higher performance is required for their commercialization. Therefore, in the present study, I endeavored to enhance the thermoelectric performance of the chalcogenide materials by importing both nanotechnology and crystal alignment technique. I theoretically designed chemical reactions to obtain the chalcogenide-based materials composed of nanoparticles, and thus I successfully synthesized the materials. In addition, the prepared materials were exposed to strong magnetic field so that the crystals in the materials were successfully aligned. It was confirmed that the thermoelectric properties of chalcogenide-based materials were remarkably improved with the series of reforming process. The suggested process was completely established to obtain the stable increase in thermoelectric performance in present study, and it should be evaluated as one of the excellent methods, which can bring the commercialization of the materials forward.