We will all be used to the thermoelectric effect in our electronic devices. The property of a junction of dissimilar conductors to either generate electricity from a difference in temperature (the Seebeck effect), or heating or cooling the junction (the Peltier effect). Every time we use a thermocouple or one of those mini beer fridges, we’re taking advantage of it.
Practical commercial thermoelectric arrays take the form of a grid of semiconductor junctions wired in series, with a cold side and a hot side. For a Peltier array the cold side drops in temperature and the hot side rises in response to applied electric current, while for a Seebeck array a current is generated in response to temperature difference between the two sides. They have several disadvantages though; they are not cheap, they are of a limited size, they can only be attached to flat surfaces, and they are only as good as their thermal bond can be made.
Researchers in Korea have produced an interesting development in this field that may offer significant improvements over the modules, they have published a paper describing a thermoelectric compound which can be painted on to a surface. The paint contains particles of bismuth telluride (Bi2Te3), and an energy density of up to 4mW per square centimetre is claimed.
This all sounds impressive, however as always there is a snag. The coating is painted on, but then it must be sintered at high temperature to form the final material. Then since the thermoelectric Seebeck effect voltage generated across a junction is tiny, some means must be arrived at to connect multiple regions of paint in series to achieve a usable voltage. The paint is produced in both n- and p-type semiconductor variants, so they appear to achieve this series connection by alternating bands of each. And finally the efficiency of the whole is only as good as the ability of its cold side to lose heat, so we are guessing to be effective it would require something extra to improve heat transfer away from it. Still, it will have a thermal bond with its substrate that is second to none and it has the potential to cover the entire surface of a hot item, so it shows considerable promise. The researchers discuss using it for power generation, but we wonder whether there is also a prospect of it being used as a Peltier effect device to provide enhanced cooling.
We’ve covered many conventional thermoelectric generators in the past. The smallest was probably this LED ring, but we’ve also shown you a thermoelectric charger for use in rural Mongolia, and this very neat candle-powered fan.
Thanks to [Jack Laidlaw].
Filed under: chemistry hacks, green hacks
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