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A team of physicists from the University of Arkansas has built a circuit that can capture graphene's thermal motion and convert it to an electrical current.
"A graphene-based energy-harvesting circuit may be put onto a chip to supply clean, infinite, low-voltage power for small devices or sensors," said Paul Thibado, a physics professor and the discovery's lead researcher.
The
findings, which were published in the journal Physical Review E, back up a
notion proposed three years ago by physicists at the University of Alberta that
freestanding graphene—a single sheet of carbon atoms—ripples and buckles in a
way that may be used to gather energy.
The idea
of harvesting energy from graphene is contentious since it contradicts
physicist Richard Feynman's well-known claim that atoms can't conduct work due
to their thermal motion, known as Brownian motion. At room temperature,
Thibado's team discovered that the thermal motion of graphene induces an alternating
current (AC) in a circuit, a feat previously deemed unachievable.
In the 1950s, scientist Léon Brillouin wrote a seminal work rejecting the notion that harvesting energy from Brownian motion may be accomplished by adding a single diode, a one-way electrical gate, to a circuit. Knowing this, Thibado's team constructed their circuit with two diodes to convert AC to DC. Because the diodes are in opposition, enabling current to flow in both directions, they provide different routes across the circuit, resulting in a pulsing DC current that works on a load resistor.
They also
discovered that by improving their design, they were able to improve the
quantity of electricity provided. "We also discovered that the diodes'
on-off, switch-like function enhances rather than reduces the power delivered,
as previously thought," Thibado stated. "The diodes' rate of change
in resistance adds an additional element to the power."
To verify
that the diodes increased the circuit's power, the scientists used a relatively
new discipline of physics. "We used the emerging discipline of stochastic
thermodynamics to prove this power boost and extended Nyquist's almost
century-old, acclaimed theory," said coauthor Pradeep Kumar, associate
professor of physics and coauthor.
The graphene
and the circuit, according to Kumar, have a symbiotic interaction. Despite the
fact that the load resistor is being worked on by the thermal environment, the
graphene and circuit are both at the same temperature, and heat does not travel
between them.
According to Thibado, this is a critical distinction since a temperature differential between the graphene and the circuit in a circuit that produces electricity would violate the second law of thermodynamics. "This means the second law of thermodynamics isn't broken, and there's no need to claim that 'Maxwell's Demon' is separating hot and cold electrons," Thibado explained.
The
scientists also discovered that graphene's comparatively sluggish motion causes
current to flow through the circuit at low frequencies, which is essential from
a technological standpoint because electronics work better at lower
frequencies.
"Although some people believe that current going through a resistor causes it to heat up, Brownian current does not. In fact, if there was no current running through the resistor, it would cool down "Thibado clarified.”We rerouted the current in the circuit and converted it into something beneficial."
The team's
next goal is to see if DC current can be stored in a capacitor and used later,
which will need miniaturising the circuit and patterning it on a silicon wafer,
or chip. Millions of these tiny circuits might be created on a 1-millimeter by
1-millimeter chip and used to replace low-power batteries.
References:
P. M.
Thibado et al. Fluctuation-induced current from freestanding graphene, Physical
Review E (2020). DOI: 10.1103/PhysRevE.102.042101 ,
journals.aps.org/pre/abstract/ … /PhysRevE.102.042101
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