Energy

Thermoelectric generator pulls energy from room temperature heat

Thermoelectric generator pulls energy from room temperature heat
A diagram illustrating the new thermoelectric generator
A diagram illustrating the new thermoelectric generator
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A diagram illustrating the new thermoelectric generator
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A diagram illustrating the new thermoelectric generator

Scientists in Japan have developed a new organic device that can harvest energy from heat. Unlike other thermoelectric generators, this one works at room temperature without a heat gradient.

Thermoelectric devices are designed to tap into a simple law of physics: heat energy moves from hotter regions to colder ones. In these devices, electrons move from the warmer surface to the cooler one, which produces an electric current. In theory, thermoelectric generators, materials and paints could produce electricity from small temperature differences in engines, power plants, even body heat.

Usually, the bigger the temperature gradient, the better the thermoelectric generator, but now scientists from Kyushu University in Japan have found a way to harness the relatively low energy available from room temperature, without a gradient at all.

Instead, the new device works on a principle called charge separation. Heat from the ambient air causes negative electrons and positive electron “holes” in the material to separate and move in different directions, generating a current.

The materials in question are organic compounds, which can easily transfer electrons between each other. Different types of these compounds are stacked in thin layers like stairs, and the heat gives the electrons or holes enough energy to jump up to the next “step.”

After much trial and error of different compound combinations, the team settled on a device with a 180-nanometer layer of copper phthhalocyanine, 320 nm of copper hexadecafluoro phthalocyanine, 20 nm of fullerene, and 20 nm of bathocuproine.

The end result boasted an open-circuit voltage of 384 millivolts, a short-circuit current density of 1.1 μA/cm2, and a maximum output of 94 nW/cm2. That’s a tiny amount of electricity, of course, but considering it’s coming from room temperature, it could make for simpler generators.

“We would like to continue working on this new device and see if we can optimize it further with different materials,” said Professor Chihaya Adachi, lead author of the study. “We can even likely achieve a higher current density if we increase the device’s area, which is unusual even for organic materials. It just goes to show you that organic materials hold amazing potential.”

The research was published in the journal Nature Communications.

Source: Kyushu University

8 comments
8 comments
Cymon Curcumin
Over the years I’ve seen a few research teams claim to extract energy from ambient heat and producing free air conditioning as a byproduct. They always claim they don’t violate the 2nd law of thermodynamics because of reasons.

I think I will hold off on any enthusiasm for this.
TechGazer
Does this device get colder than ambient temperature while generating a current?

I wonder whether there's a temperature difference not accounted for, such as light (bright laboratory lighting!) on one side of it, and shade on the other.
rgbatduke
OK, all I can say is "no they didn't". It is left as an exercise in thermodynamics to demonstrate how this device -- if it truly operated at a constant ambient temperature to turn heat into electricity -- could be placed in an adiabatic cavity with the wires running through into a second adiabatic cavity where they run through a resistor. Result -- cavity A cools, cavity B heats, and you can run a heat engine in between the cavities -- presto, a perpetual motion machine of the first kind. Or, you can simply cool cavity A and dump the heat into the hotter outside world without the input of work -- a violation of the second law of thermodynamics. To quote Eddington, if one devises a theory (or makes claims for a device) found to violate that second law, “There is nothing for it but to collapse in deepest humiliation.” I'd be very interested in seeing how they are claiming that the organic layers behave like a de facto Maxwell's Demon. Somewhere in there, that almost certain violates detailed balance and entropy conditions, as spontaneously cooling an adiabatic reservoir (and e.g. storing the energy in a battery as it cools) causes the entropy of the Universe to DECREASE, not increase or remain the same, via a process that is itself clearly irreversible.
Douglas Rogers
If thermodynamics is violated you will get the ultraviolet catastrophy.
BanisterJH
Devices like this could work nicely in combination with heat pumps. The macro scale laws of thermodynamics don't govern quantum scale phenomena. Like many things at the quantum scale, the quantum scale laws of thermodynamics can have results that aren't necessarily intuitive to people not used to doing that math. At the macro scale, I'm certain that when you look at a system that includes mining and refining the materials and manufacturing the devices, then the macro scale laws of thermodynamics are easily satisfied.
Adrian Akau
"Heat from the ambient air causes negative electrons and positive electron 'holes' in the material to separate and move in different directions, generating a current."
This must mean that heat from the environment is being absorbed and is supplying the energy. Therefore the air must be cooling down in the process.
Marco McClean
Does it also produce reactionless thrust as a byproduct of extracting energy from the structure of spactime itself? They should put it on a sensitive scale, use electricity from it, and see if that makes it lighter or heavier during the time it's on. If it does, there's your sci-fi grav sled, and flying boots, and everything.
Karmudjun
Nice write up Michael. So the temperature causes these organic molecules to go into "Automatic" or "Programed" charge separation. One of the layers - or both - are following the rules of thermodynamics. Usually the excitation of electrons (creation of 'electron holes') requires a very minuscule heat transfer - when water evaporates in sub-zero temperature it is due to direct photon energy absorption without an adequate discernible thermal transfer - that may be what is going on here. Yet we know the rules of thermodynamics follow the adage - "There is no free lunch".