Physicists build circuit that generates clean, limitless power from
graphene
Researchers harnessed the atomic motion of graphene to generate an
electrical current that could lead to a chip to replace batteries.

Date:
October 2, 2020
Source:
University of Arkansas
Summary:
Physicists have successfully generated an electrical current from
the atomic motion of graphene, discovering a new source of clean,
limitless power.



FULL STORY ==========================================================================
A team of University of Arkansas physicists has successfully developed
a circuit capable of capturing graphene's thermal motion and converting
it into an electrical current.


==========================================================================
"An energy-harvesting circuit based on graphene could be incorporated
into a chip to provide clean, limitless, low-voltage power for small
devices or sensors," said Paul Thibado, professor of physics and lead researcher in the discovery.

The findings, published in the journal Physical Review E, are proof of
a theory the physicists developed at the U of A three years ago that freestanding graphene -- a single layer of carbon atoms -- ripples and
buckles in a way that holds promise for energy harvesting.

The idea of harvesting energy from graphene is controversial because it
refutes physicist Richard Feynman's well-known assertion that the thermal motion of atoms, known as Brownian motion, cannot do work. Thibado's
team found that at room temperature the thermal motion of graphene does
in fact induce an alternating current (AC) in a circuit, an achievement
thought to be impossible.

In the 1950s, physicist Le'on 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.

The team also discovered that the relatively slow motion of graphene
induces current in the circuit at low frequencies, which is important
from a technological perspective because electronics function more
efficiently at lower frequencies.

"People may think that current flowing in a resistor causes it to heat up,
but the Brownian current does not. In fact, if no current was flowing, the resistor would cool down," Thibado explained. "What we did was reroute
the current in the circuit and transform it into something useful."
The team's next objective is to determine if the DC current can be
stored in a capacitor for later use, a goal that requires miniaturizing
the circuit and patterning it on a silicon wafer, or chip. If millions
of these tiny circuits could be built on a 1-millimeter by 1-millimeter
chip, they could serve as a low-power battery replacement.

Video: https://www.youtube.com/watch?v=KiLTEjm8zLw&feature=emb_logo
The University of Arkansas holds several patents pending in the
U.S. and international markets on the technology and has licensed it
for commercial applications through the university's Technology Ventures division. Researchers Surendra Singh, University Professor of physics; ;
Hugh Churchill, associate professor of physics; and Jeff Dix, assistant professor of engineering, contributed to the work, which was funded by
the Chancellor's Commercialization Fund supported by the Walton Family Charitable Support Foundation.


========================================================================== Story Source: Materials provided by University_of_Arkansas. Original
written by Bob Whitby.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. P. M. Thibado, P. Kumar, Surendra Singh, M. Ruiz-Garcia,
A. Lasanta, L.

L. Bonilla. Fluctuation-induced current from freestanding graphene.

Physical Review E, 2020; 102 (4) DOI: 10.1103/PhysRevE.102.042101 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201002091029.htm

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