Physicists build circuit that generates clean, limitless power from graphene

https://phys.org/news/2020-10-physicists-circuit-limitless-power-graphene.html

by westurner • 6 years ago

42 6 6 years ago

westurner4• 6 years ago

In the 1950s, physicist Léon Brillouin published a landmark paper refuting the idea that adding a single diode, a one-way electrical gate, to a circuit is the solution to harvesting energy from Brownian motion. Knowing this, Thibado's group built their circuit with two diodes for converting AC into a direct current (DC). With the diodes in opposition allowing the current to flow both ways, they provide separate paths through the circuit, producing a pulsing DC current that performs work on a load resistor.
Additionally, they discovered that their design increased the amount of power delivered. "We also found that the on-off, switch-like behavior of the diodes actually amplifies the power delivered, rather than reducing it, as previously thought," said Thibado. "The rate of change in resistance provided by the diodes adds an extra factor to the power."
The team used a relatively new field of physics to prove the diodes increased the circuit's power. "In proving this power enhancement, we drew from the emergent field of stochastic thermodynamics and extended the nearly century-old, celebrated theory of Nyquist," said coauthor Pradeep Kumar, associate professor of physics and coauthor.
According to Kumar, the graphene and circuit share a symbiotic relationship. Though the thermal environment is performing work on the load resistor, the graphene and circuit are at the same temperature and heat does not flow between the two.
That's an important distinction, said Thibado, because a temperature difference between the graphene and circuit, in a circuit producing power, would contradict the second law of thermodynamics. "This means that the second law of thermodynamics is not violated, nor is there any need to argue that 'Maxwell's Demon' is separating hot and cold electrons," Thibado said.

rbecker• 6 years ago

I don't understand. It sounds like they're drawing useful work (I think?) from a system that's already at thermodynamic equilibrium. Doesn't that violate the 2nd law of thermodynamics?

westurner4• 6 years ago

I'm not sure that I understand either. From the abstract (which phys.org failed to link to):

The system reaches thermal equilibrium and the rates of heat, work, and entropy production tend quickly to zero. However, there is power generated by graphene which is equal to the power dissipated by the load resistor.

Looks like the article is also on ArXiV: https://arxiv.org/abs/2002.09947

https://scholar.google.com/scholar?oi=bibs&hl=en&cluster=103...

Is it really a closed system at equilibrium?

mundo• 6 years ago

The "ripple" of the graphene is described as thermal, i.e. brownian motion, so presumably this is not a closed system - i.e. the work dissipates a bit of heat from the graphene, which is replenished from the surrounding environment. I think the abstract confirms this, in that it claims the power dissipated by the load resistor equalled "power supplied by the thermal bath".

I'm no expert and this article is clickbaity, but I think the basic claim here does not sound crazy. If regular freestanding graphene does have a natural "ripple" of current caused by thermal energy[0], it seems reasonable to place an electrode very close to it and harvest the work done when charges move relative to each other. The circuit described in the youtube video[1] does seem like it would work, if the "ripple" is predictable and slow enough to switch the circuit in phase with.

It's not "limitless" obviously; it's just converting heat energy to electricity. But if this principle works, and if it can be implemented in the real world (which seems like a big if - I can imagine it being fouled up by temperature fluctuations, physical effects on the graphene like sound vibrations, etc) it sounds like it might be very useful for things like sensors with very low power needs.

0: The same team claimed to describe this in a 2014 paper - see https://phys.org/news/2014-04-track-ripples-freestanding-gra...

1: https://www.youtube.com/watch?v=KiLTEjm8zLw

westurner4• 6 years ago

Hopefully these can be sandwiched below solar panels to harvest thermal energy from the gradient.

westurner4• 6 years ago

"Fluctuation-induced current from freestanding graphene" (2020) https://journals.aps.org/pre/abstract/10.1103/PhysRevE.102.0... https://doi.org/10.1103/PhysRevE.102.042101

Physicists build circuit that generates clean, limitless power from graphene

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