From fire to electricity: Thermoelectric materials

Energy can have many forms, heat, motion and electricity being the most familiar to us. An interesting observation is that most of the ways we have found to obtain useful energy from the environment involve the emission of heat as a by-product. What if we could turn that waste useful?

Image by James Albasi. What happens when the cat is outside the box? N.B: The author has not yet found a buttercat-based power plant.

Every passing year, we need more and more energy to power every aspect of our lives. This need comes with an environmental cost, but scientific ingenuity is constantly coming up with more ways to harness the energy of the natural world.

Heat and electricity… new perspectives
During the 19th century two phenomena were discovered:

1) If we connect two metals or semiconductors (materials that allow electric current to travel with some resistance) with two different temperature sources at only one end, an electrical current would spark.

2) If we have a conductor made out of two different materials and we apply an electric voltage to it, we would sense two different temperatures.

Later on it was discovered that these two phenomena were two sides of the same coin: the conversion from heat to an electricity (1) and the conversion of electricity to heat (2). And there is where the creativity sparks with how extremely useful this process could be.

How to convert fire to lightning and storm to fire

For a long time after the theoretical discovery of thermoelectricity (conversion between heat and electrical current), it was very challenging to find materials that were able of converting heat into electricity and vice versa. But what makes a good thermoelectric material?

In a thermoelectric material, we need heat conductivity and electric conductivity to be separated, a material that can transmit electricity but not heat. But if you think about it, most widely known electric conductors are also good heat conductors.

Going a bit more into the physics, we could describe thermal conductivity as the movement of phonons and electrical currents as the movement of electrons, so a good thermoelectric material would prevent phonons to travel through the material and allow electrons to flow freely.

Since very particular properties have to be satisfied, the most promising way to engineer a good thermoelectric material is using nanoscale technologies, techniques that modify/create materials on a scale of 0.000000001 meters!

Why to do this?
The applications for thermoelectric materials have a very wide range: from everyday life to space exploration!

In the next years thermoelectric generators will be introduced in cars: it is known that a big chunk of the energy gained by burning fuel in cars goes into waste heat released through the muffler; implementing thermoelectric generators would recover some of the wasted heat to power all the auxiliary system in your cars. An analogous case can be seen for power plants.

Currently, thermoelectric generators are employed whenever we need to power something remote and sunlight is impractical, for example outside the solar system, in satellites or space probes that venture far in space. Also, back in earth, some remote lighthouses in the Arctic circle portion of Siberia. These particular types of generators use the heat released from a decaying radioactive atom.

So, if we want to increase the efficiency of cars and power plants or we need to power a machine where no man dares to venture (yet), thermoelectricity seems to be one of the prominent answers for current and future problems, in the seek of a more efficient and sustainable energy use.

James Albasi is a generic Human, chemistry graduate, currently enrolled in a physical chemistry master programme at the University of Helsinki. He loves playing music and telling unlikely stories, you can find him at concerts and comedy clubs.