Modifying the figure of merit of thermoelectric materials with inclusions of porous structures

Abstract

The overall investigation of devices when it comes to the transformation of heat flux into electrical power, and electrical energy to heat power, significantly involves thermoelectric devices (TEDs). These devices provide the potential to build clean energy using a combination of appropriate materials. It has been recognized that more than 60% of the energy generated worldwide disappears, frequently due to the heat involved (exothermic reactions, friction, combustion, and radiation). Economically feasible TED materials and devices have not been successfully developed for larger-scale industrial use due to their low efficiency, unreliability, and high cost of materials and manufacturing. In this study, simple and inexpensive materials and methods were used to tailor the properties of thermoelectric materials to improve their figure of merit, which may be of great potential for meeting future energy demand. Stoichiometric bismuth telluride (Bi₂Te₃) powder was compounded with numerous concentrations of sodium chloride (NaCl) salt particles ranging from 0 to 50% by volume. The NaCl was ground to microscale particles, and cylindrical pellets were crafted using cold pressing and sintering operations. Consequently, the NaCl was leached separately within the samples using hot water, which caused porous structures. Testing equipment was designed to measure the three essential parameters of TEDs—electrical conductivity, Seebeck coefficient, and thermal conductivity—before and after the NaCl leaching process. Following that, the figure of merit was also calculated for each concentration. Primarily porous structures containing 20% NaCl had a 37.55% higher figure-of-merit value compared to the base samples (0% NaCl), and an increase of 89.07% in the figure of merit from the solids content of the samples was observed with NaCl inclusions at a concentration of 30% by volume. The existence of both NaCl and pores was sufficient to increase the figure of merit. Inclusions and porosity detrimentally influenced the electrical conductivity, but there was a substantial rise in the Seebeck coefficient and thermal conductivity changes leading to an increase in the figure of merit. The figure of merit obtained from this study is relatively moderate for the latest generation of thermoelectric materials. However, the materials and methods used here were simple, economical, and scalable and have great potential for use with optimized thermoelectric materials in hopes of further improvement in the figure of merit.

Keywords

Thermoelectric materials / Seebeck coefficient / Thermal and electrical conductivity / Porosity / Figure of merit

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