Silver Nanoparticles for Linking Electrode Coatings and Metallization
During the last 20 years, many high-performance thermoelectric materials have been discovered. This is done in the absence of an effective device to convert the energy it generates into emission-free power. Their promise has not been fulfilled.
Image Credit: University of Houston
An international research group led by a University of Houston the physicist and many of his former students have reported a new method for constructing thermoelectric modules, with the help of silver nanoparticles, to connect the electrodes and metallized layers of the module.
The use of silver nanoparticles is tested for stability in a module made of three different advanced thermoelectric materials developed to function across a wide temperature range.
The study is reported in Natural Energy Journal on May 1st2023.
Thermoelectric materials have received great attention because of their potential as a source of clean energy, generated when they convert heat—such as waste heat generated by power plants or other industrial processes—into electricity by using a current to flow from a warmer area to a cooler area.
However, tapping into this potential means finding a material that can both thermally and electrically connect the cold and hot sides of a material without changing the material’s performance.
The bonding material, or solder, has undergone melting to create an interface between the two sides. This implies the solder must have a greater melting point compared to the operating temperature of the device.
This is done to ensure stability while the device is functioning, said Zhifeng Ren, director of the Texas Center for Superconductivity at the University of Houston (UH) and corresponding author on the study. If the thermoelectric material operates at a hotter temperature, the bonding layer will re-melt.
However, it can also be a problem if the joining material consists of a melting point that is too high because high temperatures can affect the performance and stability of the thermoelectric material during the joining process.
In addition, the ideal bonding material would both have a relatively low melting point for the module assembly so as not to destabilize the thermoelectric material but then be able to withstand high operating temperatures without re-melting.
Silver contains properties useful for such a bonding material, having high electrical conductivity and high thermal conductivity. However, it also has a relatively high melting point, at 962 °C, which can affect the stability of some thermoelectric materials.
To make this work possible, scientists benefit from the fact that silver nanoparticles consist of a much lower melting point than bulk silver. The nanoparticles return to a bulk state after module assembly, thereby regaining a greater melting point for operation.
If you make silver into nanoparticles, the melting point can be as low as 400 degrees or 500 degrees C, depending on the size of the particles. This means you can use your device at 600 C or 700 C without issue, as long as the operating temperature stays below the melting point of bulk silver, or 962 C..
Zhifeng Ren, Author and Corresponding Director of Studies, Texas Center for Superconductivity, University of Houston
Ren worked on the project with five former students and postdoctoral scientists from Ren’s research group. They are currently at the Harbin Institute of Technology in China, Shenzhen, and the Beijing National Laboratory for Condensed Matter Physics at the Chinese Academy of Sciences in Beijing.
The silver nanoparticles were tested by scientists with three well-known thermoelectric materials, each of which functions at a different temperature.
According to the scientists, the lead tellurium-based module, which operates at low temperatures of about 573 K to about 823 K (300 °C to 550 °C), achieves a heat-to-electricity conversion efficiency of almost 11% and remains stable after 50 thermal cycles.
In addition, they utilized silver nanoparticles as a bonding material in the modules with the help of low temperature bismuth telluride and half Heusler high temperature materials. This shows the idea would work for a variety of thermoelectric materials and purposes.
Various materials are used based on the intended heat source, says Ren, to ensure they can withstand the heat applied.
But this paper proves that regardless of the material, we can use the same silver nanoparticles for solder as long as the heat applied does not exceed 960 degrees C.
Zhifeng Ren, Corresponding Author of the Study and Director of the Texas Center for Superconductivity, University of Houston
This is done to make the melting point of bulk silver lower.
In addition to Ren, co-authors of the study include Li Yin, Fan Yang, Xin Bao, Zhipeng Du, Xinyu Wang, Jinxuan Cheng, Hongjun Ji, Jiehe Sui, Xingjun Liu, Feng Cao, Jun Mao, Mingyu Li, and Qian Zhang, all with Harbin Institute of Technology; Wenhua Xue with the Harbin Institute of Technology and the Beijing National Laboratory of Condensed Matter Physics; and Yumei Wang with the Beijing National Laboratory of Condensed Matter Physics.
Journal Reference
Yin, L., et al. (2023) Low temperature sintering of Ag nanoparticles for the design of high performance thermoelectric modules. Natural Energy. doi.org/10.1038/s41560-023-01245-4.
Source: https://www.uh.edu/
