Thermoelectric properties of PbTe based single-walled carbon nanotube (SWCNT) composites

Abstract

Thermoelectric has long been recognized as a promising technology due to its ability to harvest waste heat from different sources, such as the Sunlight, vehicles, and energy-intensive industries, and thereby convert it into electricity without emitting greenhouse gases, so providing distributed solutions for sustainable energy challenges and energy efficiency issues worldwide. Lead Telluride (PbTe) is the classic thermoelectric material; however, its applications are limited by its low efficiency. The goal of the present research is to improve the energy conversion efficiency of PbTe by mixing single-walled carbon nanotubes (SWCNTs) via simple powder processing and utilizing nanostructuring and quantum confinement effects in a synergistic way. PbTe based composites incorporating different vol% of SWCNTs were fabricated through the high-frequency induction heating furnace at ~450°C. Thermoelectric characteristics of bulk samples were tested at temperatures ranging from ~300 to ~530K. With the inclusion of nanotubes, the electrical conductivity behaviour changes from semi-metallic in pristine PbTe to semi-conducting in composites. This shows that the semiconducting nature of SWCNTs plays a major role in electrical transport. As a result, the composites’ effective electrical conductivities were lowered near room temperature, with the lowest values observed at 0.5 vol% of SWCNTs. When compared to pure PbTe, the Seebeck coefficient of the 0.5 vol% of PbTe composite improves at ambient temperature and gradually drops after ~375K. Thermal conductivity of all the composites reduces and substantial reduction was observed at 0.5 vol% of SWCNTs. The large transition from semi-metallic to semi-conducting transport in pristine PbTe to composites, as well as enhanced short-range carrier scattering, are responsible for lowering electrical conductivity and hence composites’ power factor. As a result, the significant reduction in thermal conductivities could not compensate for the loss of power factor, resulting in lower ZT values from pristine PbTe.