Long thought to be physically impossible: a nonlinear circuit uses graphene to harness its own energy

This discovery challenges more than a century of physical orthodoxy by identifying a new kind of energy that can be extracted from ambient heat using graphene.

It has long been believed to be difficult to produce useful work from random oscillations in a thermally balanced system. In fact, the eminent American physicist Richard Feynman effectively put an end to all research in the 1960s after arguing in a number of conferences that the brownian motion, or the thermal motion of the atomes, cannot perform any useful work.

Feynman did, however, make an important discovery, as evidenced by a recent study titled "Charging the Condensators from Thermal Fluctuations with the Help of Diodes" that was published in the journal Physical Review E.

Three of the article's five authors are alumni of the University of Arkansas's physical education department. Paul Thibado, the study's lead author, claims that their research rigorously demonstrates that when an autonomous graphene is connected to a circuit that includes nonlinear resistance diodes and storage condensers, the graphene's thermal fluctuations produce work that is useful for charging the storage condensers.

Empirical evidence supporting the finding

Scientists have discovered that when storage capacitors have an initial charge of zero, the circuit draws energy from the thermal environment to charge them. The team then demonstrated that the system satisfies both the first and second laws of thermodynamics throughout the charging process. They also found that larger storage capacitors produce more stored charge, and that smaller graphene capacitance provides both a higher initial charge rate and a longer discharge time. These characteristics are important because they allow time to disconnect the storage capacitors from the energy harvesting circuit before the net charge is lost.

This latest publication builds on two of the group's previous studies. The first was published in a 2016 Physical Review Letters article titled “Anomalous Dynamic Behavior of Freestanding Graphene Membranes.” In this study, Thibado and his co-authors identified the unique vibrational properties of graphene and its potential for energy harvesting. The second was published in a 2020 Physical Review E paper titled “Fluctuating Induced Current from Autonomous Graphene,” in which they discuss a circuit using graphene that can provide unlimited clean power for small devices. or sensors.

This latest study goes one step further by mathematically establishing the design of a circuit capable of capturing heat energy from the earth and storing it in capacitors for later use.

"Theoretically, that's what we wanted to prove," Thibado explained. “There are well-known sources of energy, such as kinetic, solar, ambient radiation, acoustic and thermal gradients. Now there is also a nonlinear thermal power. Usually, people imagine that thermal energy requires a temperature gradient. It is, of course, an important source of practical power, but what we have found is a new source of power that has never existed before. And this new power does not require two different temperatures because it exists at one temperature.

Besides Thibado, co-writers include Pradeep Kumar, John Neu, Surendra Singh, and Luis Bonilla. Kumar and Singh are also professors of physics at the University of Arkansas, Neu at the University of California, Berkeley, and Bonilla at Carlos III University in Madrid.

A decade of investigation

The study represents the solution to a problem Thibado has studied for more than a decade, when he and Kumar first tracked the dynamic motion of ripples in free-standing graphene at the atomic level. Discovered in 2004, graphene is a sheet of graphite one atom thick. The duo observed that free-standing graphene has a wavy structure, with each ripple oscillating up and down in response to ambient temperature.

“The thinner something is, the more flexible it is,” Thibado said. "And at just an atom thick, there's nothing more flexible. It's like a trampoline, constantly going up and down. If you want to keep it from moving, you have to cool it down to 20 Kelvin.

His current efforts in developing this technology focus on building a device he calls a Graphene Energy Harvester (or GEH). GEH uses a negatively charged graphene sheet suspended between two metal electrodes. When the graphene flips over, it induces a positive charge in the top electrode. When it swings down, it positively charges the lower electrode, creating an alternating current. With diodes wired in opposition, allowing current to flow in both directions, separate paths are provided through the circuit, producing a pulsating direct current that performs work on a load resistor.