The quest for cleaner, dependable energy sources is a global imperative. Beyond harnessing the power of sun and wind, scientists continue to push for inventive solutions in pursuit of this goal.

Recently, a team of researchers has taken an interesting approach where they have chosen to focus on a more microscopic solution: Could energy be generated at the molecular level?

The idea is based on the concept of wave energy, a renewable and sustainable source of electricity that is generated by harnessing kinetic energy created by the movement of ocean waves and captured using various technologies.

For Yucheng Luan, a scientist and founder of the East Eight Energy Co., Ltd. in China, the connection was a simple one. “I became particularly interested in energy more than a decade ago, especially in finding new sources of green energy,” explained Luan in an email. “I saw dust moving in the air and I thought it would be very interesting if molecular […] motion could be converted into electricity.”

Even when a liquid is stationary, its molecules remain in perpetual motion, constantly vibrating, twisting, and revolving around each other. Consider an ideal gas as an illustration: At room temperature, the average kinetic energy per mole of gas molecules is approximately 3.7 kJ, which can be roughly equated to powering a small light bulb for 30 seconds.

“There are vast amounts of air and liquid on Earth, and their successful harvesting could produce a gigantic amount of energy for society,” said Luan.

If this form of perpetual energy could be tapped in to, it would potentially provide a new source of hypothetically clean energy on an enormous scale.

A nanoscale generator

This movement of molecules is called molecular thermal motion and represents a distinct and unique form of dynamic movement that sets it apart from conventional mechanical motion. It is an integral part of any physical system’s internal energy, where the molecules within all substances exhibit perpetual and erratic motion when the material’s temperature is above absolute zero.

“Molecular thermal motion harvester devices do not need any external stimulation, which is a big advantage compared with other energy harvesters,” Luan said. “At present, electrical energy is mainly obtained by external energy, such as wind energy, hydroelectric energy, solar energy, and others. This work opens up the possibility of generating electrical energy through the molecular thermal motion of liquids, from the internal energy of the physical system that is essentially different from ordinary mechanical motion.”

While working in the field of nanomaterials, Luan believed that finding a solution using nanotechnology would allow him to capture this molecular thermal motion and convert it into usable electricity.

The team therefore created a nanoscale energy-harvesting device from a peizoelectric material called zinc oxide, which generates an electrical current when under pressure or mechanical stress. The zinc oxide was arranged into arrays of microscopic wires akin to a field of seaweed, capable of swaying within the surrounding liquid.

“As a well-studied piezoelectric material, zinc oxide can be easily synthesized into various nanostructures, including nanowhiskers,” Luan said. “A nanowhisker is a neat and orderly structure of many nanowires, similar to the bristles on a toothbrush.

“The random collision of liquid molecules drive the nanoarrays to [deform], generating electricity,” he added. “[The device’s] output voltage and current can reach 2.28 mV and 2.47 nA at room temperature. The power of the device is still very small and unable to power a light bulb at the current stage. However, the second generation of the devices is currently progressing very well in our lab, which could light the bulbs.”

The team say that near-future applications could include powering microwatt scale devices, such as brain computer interfaces, wearable devices, and implantable medical devices, but the technology could be scaled to full-size generators and kilowatt-scale energy production.

“If we are lucky enough, we think some practical applications could be realized within 8-12 months,” said Luan. “The hurdle is recruiting more talented scientists and engineers to join our adventure!”

Reference: Yucheng Luan, et al., Molecular thermal motion harvester for electricity conversion, APL Materials (2023). DOI: 10.1063/5.0169055

Feature image credit: Pawel Czerwinski on Unsplash