Thermoelectric generators operating at room temperature will soon become a reality
Thermoelectric (TE) generators are something that has long been viewed as a promising technology suitable for converting heat simply emitted into the environment with exhaust gases from automobiles or industrial plants, for example, into electrical energy. Despite the mass of research carried out in this direction, the created thermoelectric generators are devices that operate at sufficiently high temperatures. Recently, however, researchers from Osaka University, together with engineers from Hitachi, Ltd., have developed a new material with sufficiently high thermoelectric parameters and efficiency at room temperature.
Thermoelectric generators, made of special materials, generate an electric current if one side is hotter than the other. In addition, the thermoelectric effect can work in the opposite direction, regulating the electric current through the material supplied from an external source, it is possible to maintain a predetermined temperature gradient between the sides of the material. All thermoelectric materials have a sufficiently high electrical conductivity, plus a low thermal conductivity, which does not allow arbitrary leveling of the temperature gradient. The efficiency of a thermoelectric material is expressed by the value of a parameter called the power factor, which is proportional to the electrical, thermal conductivity and a constant called the Seebeck coefficient.
“Unfortunately, the majority of thermoelectric materials contain rare and expensive or toxic elements,” the researchers write. “We combined common and common silicon with ytterbium to obtain ytterbium silicide (YbSi2). We made a choice in favor of ytterbium for several reasons. Firstly, most of its compounds conduct electricity well, and secondly, ytterby silicide is a non-toxic material. In addition, the material has a unique property called valence fluctuations, which makes it an effective thermoelectric material at normal ambient temperatures. “
Some of the ytterbium atoms that make up YbSi2 have a valency of +2, and the other part – +3. At the same time, a “vibrational effect” constantly occurs in the material, called the Kondo resonance, when the valence of atoms begins to change from one value to another and vice versa. All this increases the value of the Seebeck coefficient and provides a fairly strong thermoelectric effect at room temperature.
Another advantage of YbSi2 is its unusual “layered” structure. Ytterbium atoms form crystallographic planes similar to those that exist in pure metal. Silicon atoms form sheets with a hexagonal lattice resembling graphite, located between the crystallographic planes of ytterbium. Such a structure effectively suppresses the specific thermal conductivity of the material, and even greater suppression of thermal conductivity can be achieved by introducing defects, impurities into the material and creating nanoscale structures.
As a result of all the efforts of scientists, the new material demonstrates a high power factor of 2.2 mW / m * K ^ 2 at room temperature. This indicator is already comparable to that of the most efficient thermoelectric materials based on toxic bismuth telluride. “Successful use of ytterbium demonstrates that by selecting the ‘right’ materials, one can obtain the necessary set of parameters required to ensure the high efficiency of a thermoelectric material,” says Ken Kurosaki. “And thermoelectric generators made from such materials will allow us to energy losses arising from the daily use of common household technologies. “So
urce: www.dailytechinfo.org