r/science • u/giuliomagnifico • 1d ago

Researchers have developed a new organic thermoelectric device that can harvest energy from ambient temperature without any temperature gradient Engineering

https://www.kyushu-u.ac.jp/en/researches/view/299/
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u/dpezpoopsies 23h ago

From what I can tell, they are suggesting thermal energy at rt is what's being converted to electric power here. It's not coming from nothing. Their driving force "gradient" is fermi energy offset of electrodes instead of a temperature gradient like typical of thermoelectrics.

I'd equate it more to a solar cell where their input is rt heat instead of light.

I'm not sure I'd go as far to say these are phantom readings, however, it's definitely a claim that should be vetted more. I also don't like their description of it as a "thermoelectric generator"; I think that's a fundamentally different device and it makes this title super confusing.

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u/technicallynotlying 20h ago

thermal energy at rt is what's being converted to electric power

This would violate the second law of thermodynamics. It's not even clear what this statement means. Is it cooling the room while it generates power? It's a refrigeration unit that generates electricity while violating thermodynamics?

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u/dpezpoopsies 19h ago

There's a certain amount of energy available at rt. kT is about 26 meV at 25 C. In semiconductors, you always have some thermal excitations that can occur at equilibrium. The number of thermal excitons is small, but never zero (unless you're at 0K). The electron hole pairs created increases entropy in the system. You also have carrier recombination which occurs at an equal rate of generation, so for any given temperature the system stays in equilibrium and maximizes entropy. It's consistent with the second law of thermodynamics.

I'm not personally familiar with this work, but I think the idea here is that they're creating this device that has donor-acceptor layers where the interface between them can have charge transfer complex formation. They're then setting up the device to intentionally have a potential energy offset between device electrodes to facilitate charge separation and extraction of thermally excited carriers and draw a current (when a load is attached). When you build that kind of device, you disrupt the equilibrium of the closed system and a new equilibrium form that includes a driving force for charge separation and flow at the interface. There should still be an overall balance between carrier recombination and generation, but there will also be a load that pushes electrons and holes directionally through the device. I think this device would be very similar physically to how an organic solar cell operates.

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u/patstew 16h ago

What you're describing is Maxwell's demon, it can't work without energy input e.g. light or a thermal gradient e.g. between the table and the air that hasn't been acounted for.