thermo electric generator concept

The concept of thermoelectric generator is old but these days it is getting more attention of the researchers. As you know the IoT is in trend and the sensors used in it need power but to connect all of them from wire is not possible. These newly developed thermoelectric materials could easily solve the problem.

Highlights:

  • Hydrogel, a special type of gel that consists of a polyacrylamide framework infused with water and specific ions. It can generate electricity from waste heat of electronic devices.
  • A thin, nontoxic iron-based generator uses waste heat to provide small amounts of electricity. It works on ANE effect and the cheapest of its kind.
  • The most effective thermoelectric known till date is Heusler alloy having ZT 5-6.



Thermoelectrics are the material that can convert heat into electrical energy. This is due to the so-called Seebeck effect: If there is a temperature difference between the two ends of a theroelectric material, the potential difference is generated and thus current starts to flow.

Hydrogel: a liquid thermoelectrics

hydrogelWe all know using electronic devices for too long can cause them to overheat, which might slow them down, damage their components or even make them explode or catch fire. Now, researchers have developed a hydrogel that can both cool down electronics, such as cell phone batteries, and convert their waste heat into electricity.

Until now the devices made by scientists can either convert waste heat into electricity or cool the gadgets. But a team of researchers led by Xuejiao Hu, Kang Liu, Jun Chen and their colleagues have made a special type of thermo galvanic hydrogel that can convert waste heat into electricity, simultaneously lowering the temperature of the device.

The hydrogel is made up of a polyacrylamide framework infused with water and specific ions. When they heated the hydrogel, two of the ions (ferricyanide and ferrocyanide) transferred electrons between electrodes, generating electricity. Meanwhile, water inside the hydrogel evaporated, cooling it. After use, the hydrogel regenerated itself by absorbing water from the surrounding air.


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To demonstrate the new material, the researchers attached it to a cell phone battery during fast discharging. Some of the waste heat was converted into 5 μW of electricity, and the temperature of the battery decreased by 68 degree F. The reduced working temperature ensures safe operation of the battery, and the electricity harvested is sufficient for monitoring the battery or controlling the cooling system.

The paper was published in DOI: 10.1021/acs.nanolett.0c00800



Iron-based binary ferromagnets for transverse thermoelectric conversion

A team of researchers from University of Tokyo Institute for Solid State Physics have found a way to convert heat energy into electricity with a nontoxic material. The material is mostly iron which is extremely cheap given its relative abundance. A generator based on this material could power small devices such as remote sensors or wearable devices. The material can be thin so it could be shaped into various forms.

thermo electric generator concept
Thermoelectric devices based on the anomalous Nernst effect (left) and the Seebeck effect (right). (V) represents the direction of current, (T) the temperature gradient and (M) the magnetic field. Credit: © 2020 Sakai et al

The thermoelectric devices are mainly based on Seebeck effect and a less popular anomalous Nernst effect ANE. This experiment is based on ANE

ANE produces a voltage perpendicular to the direction of a temperature gradient across the surface of a suitable material. The phenomenon could help simplify the design of thermoelectric generators and enhance their conversion efficiency if the right materials become more readily available.

thermoelectric new research
A diagram to show the nodal web structure responsible for the anomalous Nernst effect. Credit: © 2020 Sakai et al

This material is a composite of 75 percent iron and 25 percent aluminum (Fe3Al) or gallium (Fe3Ga) made by a process called doping. The newly developed material has twentyfold jump in voltage compared to other undoped samples.

This thin and flexible structures could harvest energy more efficiently than generators based on the Seebeck effect. this technology can be used to power wearable devices or remote sensors in inaccessible places where batteries are impractical.

The findings was submitted to nature journal



The most effective thermoelectric material made till now Heusler alloy

heusler alloyThe amount of electrical energy that can be generated at a given temperature difference in a thermoelectric device is measured by the so-called ZT value: The higher the ZT value of a material, the better its thermoelectric properties.

The best thermoelectric devices known till date were measured at ZT values of around 2.5 to 2.8. Scientists at TU Wien (Vienna) have now succeeded in developing a completely new material with a ZT value of 5 to 6. It is a thin layer of iron, vanadium, tungsten and aluminium applied to a silicon crystal.

The atoms in this material are usually arranged in a strictly regular pattern in a so-called face-centered cubic lattice. The distance between two iron atoms is always the same, and the same is true for the other types of atoms. Thus the whole crystal has a complete regular structure.


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However, when a thin layer of the material is applied to silicon, something amazing happens: the structure changes radically. Although the atoms still form a cubic pattern, they are now arranged in a space-centered structure, and the distribution of the different types of atoms becomes completely random.

This mixture of regularity and irregularity of the atomic arrangement also changes the electronic structure, which determines the electrons movement in the solid.

The electrical charge moves through the material in such a way that it is protected from scattering processes. In this way, a very low electrical resistance is achieved.

The portions of charge traveling through the material are referred to as Weyl Fermions.

Lattice vibrations, on the other hand, which transport heat from places of high temperature to places of low temperature, are inhibited by the irregularities in the crystal structure. Therefore, thermal conductivity decreases.

This is important if electrical energy is to be generated permanently from a temperature difference – because if temperature differences could equilibrate very quickly and the entire material would soon have the same temperature everywhere, the thermoelectric effect would come to a standstill.

The new material has now been presented in the journal Nature.



Applications of thermoelectric materials

In internet of things these materials could be much useful as it could provide energy for sensors and small electronic applications. The demand for such small-scale generators is growing quickly. because for large no. of sensors in a factory it is not possible to connect all the sensors with wire. More and more devices are linked together online so that they automatically coordinate their behavior with each other.

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