High-efficiency half-Heusler thermoelectric modules enabled by self-propagating synthesis and topologic structure optimization

Abstract

Combining high thermoelectric (TE) performance, excellent mechanical properties, and good thermal stability, half-Heusler materials show great potential in real applications, such as industrial waste heat recovery. However, the materials synthesis technology developed in the laboratory scale environment cannot fulfil the requirements of massive device fabrication. In this work, a batch synthesis utilizing the self-propagating high-temperature synthesis (SHS) method was used to prepare state-of-the-art n-type Zr_0.5Hf_0.5NiSn_0.985Sb_0.015 and p-type Zr_0.5Hf_0.5CoSb_0.8Sn_0.2 half-Heusler alloys. Due to the nonequilibrium reaction process, dense dislocation arrays were introduced in both n-type and p-type materials, which greatly depressed the lattice thermal conductivity. As a consequence, the zT values of samples cut from ingots weighing a few hundreds of grams compared favorably with those prepared from few gram laboratory size pellets. Based on the high TE performance, a three-dimensional finite element model encompassing all relevant parameters was applied to optimize the topological structures of both a half-Heusler single-stage module and a half-Heusler/Bi₂Te₃ segmented module. The optimized modules attained record-high conversion efficiencies of 9.6% and 12.4% for the single-stage and the segmented module, respectively. The work documents a comprehensive processing of novel TE materials culminating in the assembly of efficient TE modules. As such, it paves the way for widespread commercial applications of TE power generation.