Nanofluidic device generates energy with salt water

Newswise – Along the world's coastlines is a largely untapped source of energy: the difference in salinity between seawater and freshwater. A new nano device can use this difference to generate energy.

A team of researchers at the University of Illinois at Urbana-Champaign has published in the journal Nano Energy the design of a nanofluidic device that can convert ion flow into usable electrical energy. The team believes their device can be used to extract energy from natural ion flows at the interface between seawater and freshwater.

“Although our design is still a concept at this point, it is quite versatile and already shows strong potential for energy use,” said Jean-Pierre Lebourton, a U. professor of electrical and computer engineering and project leader. “It started with an academic question – ‘Can a nanoscale solid-state device extract energy from an ion stream?' “But our design exceeded our expectations and surprised us in many ways.”

When two bodies of water with different salinities meet, such as where a river flows into the ocean, salt molecules naturally flow from the higher concentration to the lower concentration. Energy can be harvested from these currents because they are made up of electrically charged particles called ions that are formed from the dissolved salt.

Leburton's group has designed a nanoscale semiconductor device that exploits a phenomenon called “Coulomb drag” between ions and electric charge flowing through the device. As ions flow through the device's narrow channel, electrical forces cause the device's charges to move from one side to the other, creating a voltage and an electric current.

The researchers discovered two surprising behaviors when they simulated their device. First, while they expected Coulomb drag to occur primarily through the force of attraction between opposite electric charges, the simulations showed that the device works equally well if the electric forces are neutral. Both positively and negatively charged ions contribute to traction.

“It is also noteworthy that our study indicates that there is an amplification effect,” said Mingye Xiong, a graduate student in Leburton's group and lead author of the study. “Because the moving ions are so massive compared to the charges in the device, the ions impart a large momentum to the charges, amplifying the underlying current.

The researchers also found that these effects are independent of the specific configuration of the channel, as well as the choice of materials, provided that the diameter of the channel is narrow enough to allow close proximity between ions and charges.

The researchers are in the process of patenting their findings, and they are studying how arrays of these devices can be scaled up for practical power generation.

“We believe that the power density of the devices can match or exceed that of solar cells,” Leburton said. “And that's not to mention potential applications in other areas, such as biomedical sensing and nanofluidics.”

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Kewei Song also contributed to the cause.

The researchers' article, “Ion Coulomb Drag in Nanofluidic Semiconductor Channels for Energy Harvesting,” is available online. DOI: 10.1016/j.nanoen.2023.108860