Physicists from the University of Arkansas have successfully created a circuit that’s able to capture graphene’s thermal motion and transform it into an electrical current.
The discovery, published in a paper in the journal Physical Review E., is proof of a hypothesis the scientists came up with at the University of Arkansas that freestanding graphene – a single layer of carbon atoms – wrinkles and crumples in a way that holds promise for energy harvesting.
“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 finding.
Harvesting Energy From Graphene
The concept of harvesting energy from graphene is rather arguable as it contradicts physicist Richard Feynman’s renowned assertion that the thermal motion of atoms, also known as Brownian motion, cannot do work.
However, Thibado’s team discovered that at room temperature, the thermal motion of graphene does actually create an alternating current (AC) in a circuit, something that’s previously thought to be impossible.
In the 1950s, physicist Léon Brillouin published a milestone paper contradicting the idea that adding a single diode – a one-way electrical gate – to a circuit is the answer for harvesting energy from Brownian motion. Knowing this, Thibado’s group developed their circuit with two diodes for transforming AC into a direct current (DC).
With the diodes in opposition enabling the current to move both ways, they offer separate trajectories through the circuit, generating a pulsing DC current that carries out work on a load resistor.
Moreover, they found that their design enhanced 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.”
Low-Power Battery Replacement
The team used a rather new field of physics to prove the diodes enhanced 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,” explained co-author Pradeep Kumar, associate professor of physics.
As per Kumar, the graphene and circuit have an interdependent relationship. Even though the thermal setting is performing work on the load resistor, the graphene and circuit have an identical temperature, and heat doesn’t flow between the two.
That is a significant distinction because a temperature difference between the graphene and the circuit would refute 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 physicists also found that the relatively slow activity of graphene brings current in the circuit at low frequencies, which is crucial from a technological point of view because electronics operate more efficiently at lower frequencies.
The team’s next goal is to determine if the DC current can be locked in a capacitor for later use. If millions of these small circuits could be developed on a 1-millimeter by 1-millimeter chip, they could be used as a low-power battery substitute.