Researchers have discovered a new way to extract energy from ambient heat using graphene, a two-dimensional material made of carbon atoms. This breakthrough challenges the long-held assumption that thermal fluctuations cannot perform useful work.
Graphene’s Unique Vibrational Properties
Graphene is a thin layer of carbon atoms arranged in a hexagonal lattice. It has remarkable electrical, mechanical, and thermal properties that make it suitable for various applications. One of the most intriguing features of graphene is its ability to vibrate in different modes, such as bending, stretching, and twisting. These vibrations are caused by the thermal motion of atoms at room temperature or higher.
In 2016, a team of researchers from the University of Arkansas discovered that the vibrations of freestanding graphene are not random, but rather follow a pattern called Lévy flights. This means that the graphene membrane can move over large distances without losing energy, unlike other materials that quickly dissipate heat. The researchers also found that the graphene membrane can generate an alternating current (AC) when placed in a circuit with two electrodes.
A Novel Nonlinear Circuit Design
The same team of researchers has now taken their discovery a step further by designing a novel nonlinear circuit that can harvest clean power from the thermal fluctuations of graphene. The circuit consists of two diodes with opposite polarities connected to a graphene membrane and two storage capacitors. The diodes act as rectifiers that convert the AC generated by the graphene into direct current (DC) that can charge the capacitors.
The researchers proved mathematically and experimentally that their circuit can draw power from the thermal environment and store it in the capacitors for later use. They also showed that their system satisfies both the first and second laws of thermodynamics, which govern the conservation and dissipation of energy. Moreover, they found that larger capacitors can store more charge and that smaller graphene capacitance can provide faster charging and longer discharging times.
A New Form of Thermal Power
The discovery of the nonlinear circuit overturns more than a century of physics orthodoxy that states that thermal fluctuations cannot perform useful work. This assumption was based on the work of eminent American physicist Richard Feynman, who argued in the 1960s that Brownian motion, or the random movement of particles in a fluid, cannot be harnessed for any practical purpose.
However, Feynman missed something important, according to Paul Thibado, the lead author of the study. He said that their study reveals a new form of energy that can be extracted from ambient heat using graphene. He added that this new form of thermal power does not require a temperature gradient, unlike other sources of heat energy. He also said that this new power source has promising commercial potential, especially for wireless sensors and devices.
