Selective Dissolution-Derived Nanoporous Design of Impurity-Free Bi₂ Te₃ Alloys with High Thermoelectric Performance

Thermoelectric technology, which has been receiving attention as a sustainable energy source, has limited applications because of its relatively low conversion efficiency. To broaden their application scope, thermoelectric materials require a high dimensionless figure of merit (ZT). Porous structuring of a thermoelectric material is a promising approach to enhance ZT by reducing its thermal conductivity. However, nanopores do not form in thermoelectric materials in a straightforward manner; impurities are also likely to be present in thermoelectric materials. Here, a simple but effective way to synthesize impurity-free nanoporous Bi_0.4 Sb_1.6 Te₃ via the use of nanoporous raw powder, which is scalably formed by the selective dissolution of KCl after collision between Bi_0.4 Sb_1.6 Te₃ and KCl powders, is proposed. This approach creates abundant nanopores, which effectively scatter phonons, thereby reducing the lattice thermal conductivity by 33% from 0.55 to 0.37 W m^-1 K^-1 . Benefitting from the optimized porous structure, porous Bi_0.4 Sb_1.6 Te₃ achieves a high ZT of 1.41 in the temperature range of 333-373 K, and an excellent average ZT of 1.34 over a wide temperature range of 298-473 K. This study provides a facile and scalable method for developing high thermoelectric performance Bi₂ Te₃ -based alloys that can be further applied to other thermoelectric materials.