Scientists manage to harvest energy from ripples in graphene

This innovative approach relies on out-of-the-box thinking resulting in a unique circuit design.
Tejasri Gururaj
Graphene hexagonal structure in motion
Graphene hexagonal structure in motion

Iván Jesús Cruz Civieta/iStock 

Obtaining useful energy from random fluctuations in systems at thermal equilibrium has been a long-standing challenge.

When a system is in thermal equilibrium, the particles of the system are constantly in motion due to their thermal energy. These particles move randomly, colliding with each other and exchanging energy, but the overall energy distribution remains stable.

The challenge to harness energy from this disordered motion lies in channeling this inherent energy randomness into a controlled and usable outcome.

Now, a team of scientists led by Paul Thibado from the University of Arkansas has found a way to harness energy from thermal fluctuations in graphene. The team achieved this by connecting a unique circuit to freestanding graphene, a one-atom-thick graphite sheet. 

Speaking about the team's motivation to study this topic, Thibado said in a press release, "I think people were afraid of the topic a bit because of Feynman. So, everybody just said: I'm not touching that. But the question just kept demanding our attention."

Useful work and defying Feynman

The study's journey began by questioning the assumption made by physicist Richard Feynman in the 1960s.

Feynman's lectures asserted that extracting useful work from Brownian motion was impossible, especially when systems were at the same temperature (thermal equilibrium). However, the team behind this study, including first author Paul Thibado, found something important that had been missed.

Their current study builds on a decade of inquiry by the team when Thibado, and co-author Pradeep Kumar, noticed something interesting about freestanding graphene. They observed that the graphene material naturally forms ripples on its surface. 

These ripples behave like tiny waves, moving up and down in response to changes in the surrounding temperature. 

Thibado and his team designed a unique circuit to extract energy from these ripples. The circuit consists of a junction followed by two diodes wired in opposition with a non-linear resistor. A diode is an electronic component that allows current to flow in only one direction.

The circuit design was chosen to overcome the condition set by the second law of thermodynamics, which says that useful energy can't be collected when both the circuit and the ripples are in thermal equilibrium, even if we use a diode.

Using the unique setup with two diodes, the team found that they could slow down the process.

As the circuit interacts with the particles in Brownian motion, it temporarily breaks equilibrium, allowing current to flow between the diodes and the charging of storage capacitors. This entire process occurs while adhering to thermodynamics' first and second laws.

Graphene Energy Harvester 

Thibado's commitment to unlocking the potential of graphene's properties goes beyond the theoretical realm. His efforts are focused on building a practical application known as the Graphene Energy Harvester (GEH). 

This technology aims to harness the unique flexibility of graphene, enabling it to capture energy from the environment and potentially revolutionize sustainable energy solutions.

NTS Innovations, a nanotechnology-focused company, holds an exclusive license to develop this technology commercially. The GEH, utilizing graphene's unique properties, shows promise for mass production on silicon chips. 

These small-scale GEH circuits could revolutionize wireless sensors and devices, particularly in environments where battery replacement is inconvenient or costly.

Speaking of Thibado's research, Donald Meyer, CEO of NTS Innovations, said in a press release, "Paul's research reinforces our conviction that we are on the right path with Graphene Energy Harvesting. We appreciate our partnership with the University of Arkansas in bringing this technology to market."

This study challenges a long-held assumption about energy harvesting from Brownian motion at thermal equilibrium. 

The findings of the study are published in Physical Review E.

Study abstract:

We theoretically consider a graphene ripple as a Brownian particle coupled to an energy storage circuit. When the circuit and particle are at the same temperature, the second law forbids harvesting energy from the thermal motion of the Brownian particle, even if circuit contains a rectifying diode. However, when the circuit contains a junction followed by two diodes wired in opposition, the approach to equilibrium may become ultraslow. Detailed balance is temporarily broken as current flows between the two diodes and charges storage capacitors. The energy harvested by each capacitor comes from the thermal bath of the diodes while the system obeys the first and second laws of thermodynamics.

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