A new discovery in thermoelectricity promises to deliver more green electricity and change metal prices
Researchers at the Vienna University of Technology have discovered excellent thermoelectric properties of nickel-gold alloys. These can be used to efficiently convert heat into electrical energy, avoiding complex turbine systems. Their findings were published in the journal Science Advances.
Thermoelectric technology allows the direct conversion of heat into electrical energy – and vice versa. This makes them interesting for a wide range of technological applications. In search of thermoelectric materials with the best possible properties, a research group from TU Wien studied various metal alloys. A mixture of nickel and gold proved particularly promising.
Using thermoelectrics to generate electricity is nothing new. Since the mid-20th century they have been used to generate electrical energy in space exploration, but thermoelectric materials are also used in everyday applications such as portable refrigerators. Furthermore, they could also be used in industrial settings to convert waste heat into green electricity, to name just one potential application.
How thermoelectricity works
The thermoelectric effect is based on the movement of charged particles migrating from the hotter to the colder side of a material. This results in an electrical voltage – the so-called thermoelectric voltage – which counteracts the thermally excited movement of the charge carriers. The ratio between the accumulated thermoelectric voltage and the temperature difference defines the Seebeck coefficient, named after the German physicist Thomas Johann Seebeck, which is an important parameter for the thermoelectric performance of a material. The important requirement here is that there is an imbalance between the positive and negative charges, as they compensate each other.
“Although Seebeck discovered the thermoelectric effect in common metals more than 200 years ago, nowadays metals are hardly considered thermoelectric materials because they usually have a very low Seebeck coefficient,” explained Fabian Garmroudi, first author of the study. On the one hand, metals such as copper, silver or gold have extremely high electrical conductivity; on the other hand, their Seebeck coefficient is in most cases extremely small.
Nickel-gold alloys with exceptional properties
Physicists at the Institute for Solid State Physics (TU Vienna) have now managed to find metallic alloys with high conductivity and an exceptionally high Seebeck coefficient. Mixing the magnetic metal nickel with the noble metal gold radically changes the electronic properties. As soon as the yellowish color of the gold disappears when about 10% nickel is added, the thermoelectric performance increases rapidly. The physical origin of the enhanced Seebeck effect is rooted in the energy-dependent scattering behavior of electrons – an effect fundamentally different from the thermoelectric one of semiconductors. Due to the particular electronic properties of nickel atoms, positive charges are dispersed more strongly than negative charges, resulting in the desired imbalance and thus a high thermoelectric voltage.
“Let's imagine a race between two runners, where one person runs on a clear track, but the other person has to overcome many obstacles. Naturally, the one who is on the free track advances faster than the opponent, who has to slow down and change direction much more often,” compared Andrej Pustogow, senior author of the study on the flow of electrons in metallic thermoelectrics. In the alloys studied here, the positive charges are strongly dispersed by the nickel electrons, while the negative charges can move practically undisturbed.
Record material
The combination of extremely high electrical conductivity and simultaneously a high Seebeck coefficient leads to record values of the thermoelectric power factor in nickel-gold alloys, which far exceed those of conventional semiconductors. “With the same geometry and fixed temperature gradient, it could generate many times more electrical energy than any other known material.” This energy could be the result of the exploitation of heat that would otherwise be wasted and difficult to use.
Furthermore, the use of a material such as gold, if widespread on a large scale, could also lead to an increase in the price of gold, especially in its minimum price, because it would increase its demand as an industrial material. At the same time, the high price of the metal is a limitation to its use.
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The article A new discovery in the thermoelectricity sector promises to obtain more green electricity and change metal prices comes from Economic Scenarios .
This is a machine translation of a post published on Scenari Economici at the URL https://scenarieconomici.it/una-nuova-scoperta-nel-settore-della-termoelettricita-promette-di-ottenere-piu-elettricita-verde-e-di-cambiare-le-quotazioni-dei-metalli/ on Sun, 01 Oct 2023 13:28:17 +0000.