80°
71º | 85°
72° | 78°
Thermoelectric materials, which can produce electricity from sources of heat that would otherwise be wasted, could play a significant role in the clean energy transition. However, their adoption has been hindered by the inefficiency of most current thermoelectric materials to generate sufficient power for many practical applications.
Researchers from the University of Houston and Rice University have reported a new approach to predict the realization of band convergence in a series of materials. In a paper published on May 16 in the journal Science, they demonstrated that one so-designed material, a p-type Zintl compound, offered highly efficient thermoelectric performance. The team fabricated a thermoelectric module with a heat-to-electricity conversion efficiency exceeding 10% at a temperature difference of 475 kelvin, or about 855 degrees Fahrenheit.
Zhifeng Ren, director of the Texas Center for Superconductivity at UH (TcSUH) and corresponding author for the paper, stated that the materials’ performance remained stable for more than two years. "It is normally difficult to get high performance from thermoelectric materials because not all of the electronic bands in a material contribute," Ren said. "It’s even more difficult to make a complex material where all of the bands work at the same time in order to get the best performance.”
For this work, Ren explained that they first devised a calculation to determine how to build a material in which all different energy bands could contribute to overall performance. They then demonstrated that this calculation worked both theoretically and practically by building a module to further verify its high performance at device level.
Band convergence is considered an effective approach for improving thermoelectric materials as it increases their power factor related to actual output power. Until now, discovering new materials with strong band convergence was time-consuming and resulted in many false starts. “The standard approach is trial and error,” said Ren. “Instead of doing numerous experiments, this method allows us to eliminate unnecessary possibilities that won’t yield better results.”
To efficiently predict how to create the most effective material, the researchers used a high-entropy Zintl alloy, YbxCa1-xMgyZn2-ySb2, as a case study. They designed a series of compositions through which band convergence was achieved simultaneously in all of the compositions.
The researchers started with four parent compounds containing five elements in total – ytterbium, calcium, magnesium, zinc and antimony. They ran calculations to determine which combinations of the parent compounds could reach band convergence. Once determined, they chose the best among these high-performance compositions to construct the thermoelectric device.
“Without this method, you would have to experiment and try all possibilities,” said Xin Shi, a UH graduate student in Ren’s group and lead author on the paper. “There’s no other way you can do that. Now, we do a calculation first, we design a material, and then make it and test it.”
The calculation method could be used for other multi-compound materials as well. This approach enables researchers to create new thermoelectric materials by identifying proper parent compounds and determining what ratio of each should be used in the final alloy.
In addition to Ren and Shi, authors of the paper include Dr. Shaowei Song from Texas Center for Superconductivity and Dr. Guanhui Gao from Department of Materials Science and Nanoengineering at Rice University.