SerpApi.Org
Researchers from the Institute of Science, Tokyo, have developed a new heat-to-electricity material that acts like an atomically thin film but comes in a more practical, solid crystal form.
If scaled outside of a laboratory, such a material could be used for things like designing next-generation materials for waste heat energy recovery.
This property is called “thermoelectric,” meaning it is able to generate electricity from the temperature difference between its two sides. Such a property would make it ideal for applications like factory exhausts, vehicle engines, power plants, and furnaces.
To be effective, such materials need to meet two seemingly conflicting properties. The first is that electrical charges must be able to move easily through the material.
The second is that it must also conduct heat poorly (be a good insulator) so that the temperature difference does not immediately disappear.
Getting electricity from heat
The problem at hand is that most electrically conductive materials also conduct heat well. That makes the hot and cold sides quickly equalize, clearly weakening electricity generation.
To help solve this, the research team turned to a mixture of thallium, iron, and selenium called TlFe₁.₆Se₂. This material’s internal structure resembles a layered sandwich.
It is composed of extremely thin layers of iron selenide, or FeSe, which are embedded repeatedly throughout a much larger three-dimensional crystal.
This is important because atomically thin FeSe films have unusually good electrical properties for thermoelectric generation. But films only a few atoms thick are difficult to manufacture, handle, and integrate into real machinery.
By doing this, the researchers effectively reproduced some of that ultrathin-film behavior inside a solid chunk of material. Importantly, the new crystals are designed to ensure that some iron atoms are missing, a property known as iron vacancies.
This, the researchers explain, limits the transmission of heat through the crystal via atomic vibrations called phonons. For reference, if the crystals were perfectly regular, these vibrations could travel easily.
More work needed
But with the breaks, these phonons are scattered, atomic bonds are distorted, and the whole lattice is changed so that heat can’t travel easily.
The result is an extremely low thermal conductivity of about 0.2 watts per meter-kelvin at roughly 356°F (180°C). In practical terms, the material acts almost like a thermal insulator while still producing an electrical response, quite an achievement.
As for practical use, the study has only proven the technology inside a lab. For it to be applied to actual electrical generation, researchers still need to overcome obstacles such as overall conversion efficiency.
Long-term stability, cost and scalability, strength, and performance in real locations like industrial settings also need to be tackled. The presence of thallium also introduces safety and containment issues, as it is highly toxic.
“This work demonstrates the effectiveness of a new design concept in which the functionality of low-dimensional materials is embedded within bulk crystals,” said study lead Professor Takayoshi Katase of the Materials and Structures Laboratory, Institute of Science Tokyo (Science Tokyo), Japan.
“The results provide a promising pathway for the development of next-generation thermoelectric materials that overcome conventional trade-offs between electrical and thermal transport properties,” he added.
The study has been published in the Journal of Materials Chemistry A.
