Module Engineering

P. Ying, L. Wilkens, H. Reith, N. Perez Rodriguez, X. Hong, Q. Lu, C. Hess, K. Nielsch, R. He, 
Energy and Environmental Science 15 (6), 2557-2566 (2022)

The applications of thermoelectric (TE) technology around room temperature are monopolized by bismuth telluride (Bi2Te3). However, due to the toxicity and scarcity of tellurium (Te), it is vital to develop a next-generation technology to mitigate the potential bottleneck in raw material supply for a sustainable future. Hereby, we develop a Te-free n-type compound Mg3Sb0.6Bi1.4 for near-room-temperature applications. A higher sintering temperature of up to 1073 K is found to be beneficial for reducing the electrical resistivity, but only if Mg is heavily overcompensated in the initial stoichiometry. The optimizations of processing and doping yield a high average zT of 1.1 in between 300 K and 573 K. Together with the p-type MgAgSb, we demonstrate module-level conversion efficiencies of 3% and 8.5% under temperature differences of 75 K and 260 K, respectively, and concomitantly a maximum cooling of 72 K when the module is used as a cooler. Besides, the module displays exceptional thermal robustness with a < 10% loss of the output power after thermal cycling for ∼32000 times between 323 K and 500 K. These proof-of-principle demonstrations will pave the way for robust, high-performance, and sustainable solid-state power generation and cooling to substitute highly scarce and toxic Bi2Te3.

P. Ying, H. Reith, K. Nielsch, R. He,
Small 18 (24), 2201183 (2022)

Solid-state thermoelectric (TE) technology is a promising approach to harvest low-grade waste heat (<573 K) and converts it to useful electricity in industrial and civilian settings. After decades of efforts in improving the figure-of-merit (zT) of TE materials, the development of advanced modules has started springing up in recent years. Although high-performance modules have been largely reported based on the successful material improvement, it remains less investigated how and whether the module-level designs can further increase the conversion efficiency. Herein, following the recent demonstration of a tellurium (Te)-free TE generator, an increase is demonstrated in the efficiency by reducing both the electrical and thermal energy losses through simply optimizing geometric factors of filling factor and leg-pair numbers. These module-level optimizations enable a record conversion efficiency of 8.2% under a ∆T ≈ 260 K, thus fulfilling 90% of the theoretical efficiency of the materials and solidly exceeding the Bi2Te3 modules. Furthermore, module robustness against > 10 160 thermal cycles while preserving a relative efficiency of 95% is demonstrated. These findings highlight the importance of the optimization strategy at the module level and demonstrate the feasibility of using Te-free thermoelectric compounds to harvest the omnipresent low-grade heat.

P. Ying, R. He, J. Mao, Q. Zhang, H. Reith, J. Sui, Z. Ren, K. Nielsch, G. Schierning, 
Nature Communications 12 (1), 1121 (2021)

Thermoelectric technology converts heat into electricity directly and is a promising source of clean electricity. Commercial thermoelectric modules have relied on Bi2Te3-based compounds because of their unparalleled thermoelectric properties at temperatures associated with low-grade heat (<550 K). However, the scarcity of elemental Te greatly limits the applicability of such modules. Here we report the performance of thermoelectric modules assembled from Bi2Te3-substitute compounds, including p-type MgAgSb and n-type Mg3(Sb,Bi)2, by using a simple, versatile, and thus scalable processing routine. For a temperature difference of ~250 K, whereas a single-stage module displayed a conversion efficiency of ~6.5%, a module using segmented n-type legs displayed a record efficiency of ~7.0% that is comparable to the state-of-the-art Bi2Te3-based thermoelectric modules. Our work demonstrates the feasibility and scalability of high-performance thermoelectric modules based on sustainable elements for recovering low-grade heat.