(Nanowerk News) Obtaining useful work from random fluctuations in a system at thermal equilibrium has long been considered impossible. In fact, in the 1960s eminent American physicist Richard Feynman effectively shut down further inquiry after he argued in a series of lectures that Brownian motion, or the thermal motion of atoms, cannot perform useful work.
Three of the paper’s five authors are from the University of Arkansas Department of Physics. According to first author Paul Thibado, their study rigorously proves that thermal fluctuations of freestanding graphene, when connected to a circuit with diodes having nonlinear resistance and storage capacitors, does produce useful work by charging the storage capacitors.
The authors found that when the storage capacitors have an initial charge of zero, the circuit draws power from the thermal environment to charge them. The team then showed that the system satisfies both the first and second laws of thermodynamics throughout the charging process. They also found that larger storage capacitors yield more stored charge and that a smaller graphene capacitance provides both a higher initial rate of charging and a longer time to discharge. 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 (“Anomalous Dynamical Behavior of Freestanding Graphene Membranes”). In that 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 article (“Fluctuation-induced current from freestanding graphene”), in which they discuss a circuit using graphene that can supply clean, limitless power for small devices or sensors.
This latest study progresses even further by establishing mathematically the design of a circuit capable of gathering energy from the heat of the earth and storing it in capacitors for later use.
“Theoretically, this was what we set out 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 nonlinear thermal power. Usually, people imagine that thermal power requires a temperature gradient. That is, of course, an important source of practical power, but what we 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 a single temperature.”
