The low melting point of nanoparticles and the high melting point of bulk silver allow the thermoelectric module to operate in a wide range of operating temperatures. Silver Nanoparticles Trigger Key Advances in Thermoelectricity for Power Generation
Many high-efficiency generators have been discovered over the past two decades, but without efficient devices to convert the energy they generate into energy without emissions, the promise has not been fulfilled them. Now, an international group of scientists led by the University of Houston physicist and many of his first students reported a new approach to building a thermoelectric module, using silver nanoparticles to connect the electrode and the metallization of the module.
It is expected that the project, described in a paper published on May 1 in Nature Energy, will lead to the development of advanced modules for generating energy and other uses. The use of silver nanoparticles was tested for stability in a module made of three different state-of-the-art electronic devices designed to operate across a range of temperatures.
Heat exchangers are attracting growing interest because of their potential as a source of clean energy, which is produced when the material changes heat – like heat generated by heat in a furnace or other production process – into electricity by using energy to pump heat from the area of the furnace, move to a cool place. But to use this ability, it is necessary to find something that can connect the hot and cold parts to the electricity and heat, without any restrictions on the performance of the material.
A bonding agent, or solder, is melted to create a gap between the two parts. That means the solder must have a melting point higher than the temperature of the device to remain stable while the device is in operation, said Zhifeng Ren, director of the Texas Center for Superconductivity at UH and corresponding author of the paper. said the body. If the thermoelectric material works at high temperatures, the bonding layer will melt again.
But it can also be a problem if the connection material has a high melting point, because the high temperature can affect the stability and performance of the heating elements during the connection process. A good quality compound will also have a low melting point for the module assembly, so as not to damage the heat exchanger, and it will be able to withstand high operating temperatures without melting.
Silver has interesting properties for such a connector, with high temperature sensitivity and high electrical conductivity. But it also has a very high melting point, at 962 degrees Centigrade, which can affect the stability of many flammable materials. For this project, researchers took advantage of the fact that silver nanoparticles have a lower melting point than bulk silver. Nanoparticles return to the raw state after the assembly of the module, regaining the highest melting point for work.
“If you turn 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 that you can operate the device at 600 C or 700 C without problems, as long as the operating temperature remains below the melting point of silver, or 962 C,” Ren, who is also a professor of Physics MD Anderson said at UH. He is working on the project with five undergraduate students and post-doctoral researchers from Ren’s research group; they are currently at the Harbin Institute of Technology in Shenzhen , China, and the Beijing National Medical Laboratory and the Chinese Academy of Sciences in Beijing.
The researchers tested silver nanoparticles on three well-known thermoelectric materials, each of which works at different temperatures.
The conductive tellurium module, which operates at a low temperature of about 573 Kelvin to about 823 K (300 C to 550 C) produces an electric power efficiency of about 11% and remains stable after 50 heat cycles, according to the researchers.
They also used silver nanoparticles as a connective material in modules using bismuth tellurid at low temperature and a high temperature material with half-heusler, indicating that the concept would work for a variety of thermoelectric materials and for purposes.
Different materials are used depending on the heat source, said Ren, to ensure that materials can withstand applied heat. “But this article shows that regardless of the material, we can use the same silver nanoparticles for soldering as long as the applied temperature does not exceed 960 degrees C”, to be below the melting point of silver and big, he said.
Source: University of Houston
