Realization of a Robust High-Efficiency n-Type Mg3(Sb, Bi)2/p-Type MgAgSb-Based Thermoelectric Power Generator for Harvesting Low-Grade Waste Heat

Abstract

Thermoelectric generators (TEGs) enable direct conversion of waste heat into electrical energy. Although Bi₂Te₃-based alloys have long been the conventional thermoelectric materials, concerns over their toxicity and limited availability have encouraged the development of sustainable alternatives. This study presents a tellurium-free TEG module based on optimized n-type Mg₃(Sb, Bi)₂, a solid solution of Mg₃Sb₂ and Mg₃Bi₂, and p-type MgAgSb as promising alternatives to conventional Bi₂Te₃-based thermoelectric materials. Both materials were synthesized using scalable vacuum-melting methods and exhibited enhanced thermoelectric performance, which was attributed to improved weighted mobility and reduced lattice thermal conductivity. Low-resistance metallic contacts with a specific contact resistivity of approximately 15–20 μΩ·cm² were successfully fabricated on both materials using a “monobloc” sintering method. An 11 p−n couple TEG module fabricated from these materials achieved a conversion efficiency of approximately 7.1% at a temperature difference of 250 K, in good agreement with simulation predictions. Moreover, at a temperature difference of 300 K and a hot end temperature of approximately 603 K, the TEG module achieved a conversion efficiency of approximately 8.5%, surpassing the performance of state-of-the-art Bi₂Te₃-based modules under comparable operating conditions.