The key to creating energy out of thin air is nanopores. Derek Lovley/Ella Maru Studio is credited.
Recent research by an engineering team at the University of Massachusetts Amherst has demonstrated that almost any material can be used to create a gadget that continuously generates power from air humidity. The key is to be able to strew nanopores smaller than 100 nanometers in diameter across the material. The study was published in Advanced Materials.
The lead author of the research, Xiaomeng Liu, is a graduate student in electrical and computer engineering at the University of Massachusetts Amherst’s College of Engineering. “This is very exciting,” she says. “We are opening up a wide door for harvesting clean electricity from thin air.”
According to Jun Yao, the senior author of the research and an assistant professor of electrical and computer engineering in the College of Engineering at UMass Amherst, “the air contains an enormous amount of electricity.” “Consider a cloud, which is merely an accumulation of water gouttes. We don’t know how to consistently gather electricity from lightning, but each of those droplets has a charge, and under the correct circumstances, the cloud can produce a lightning bolt. We have constructed a small-scale, human-built cloud that produces electricity for us predictably and continuously so that we can harvest it.”
The “generic Air-gen effect,” which Yao and his colleagues refer to as the “heart” of the artificial cloud, is what drives the system. Previous research conducted in 2020 by Yao and co-author Derek Lovley, Distinguished Professor of Microbiology at UMass Amherst, demonstrated that power could be continuously extracted from the atmosphere using a specialized material made of protein nanowires grown from the bacteria Geobacter sulfurreducens.
“What we realized after making the Geobacter discovery,” Yao explains, “is that the ability to generate electricity from the air—what we then called the ‘Air-gen effect’—turns out to be generic: literally any kind of material can harvest electricity from air, as long as it has a certain property.”
That attribute? “It needs to have holes smaller than 100 nanometers (nm), or less than a thousandth of the width of a human hair.”
The reason for this is a property called the “mean free path,” which measures how far a single molecule of a material—in this case, water in the air—travels before coming into contact with another single molecule of the same substance. The typical free path of water molecules in the atmosphere is around 100 nm.
Yao and his associates came to the realization that they could base the design of an electricity harvester on this figure. A thin layer of material having nanopores (less than 100 nm) that allow water molecules to go from the upper to the lower part of the material would be used to create this harvester. However, as the water molecules move through the thin layer, they would constantly collide with the pore’s border due to its small size. This implies that a charge imbalance, like to that found in a cloud, would result from the upper part of the layer being subjected to a greater number of charge-carrying water molecules than the lower part. This would cause the upper part of the layer to become more charged than the lower part. In essence, this would produce a battery—one that operates as long as there is any humidity in the air.
“The idea is simple,” Yao asserts, “but it’s never been discovered before, and it opens all kinds of possibilities.” Almost any type of material might be used to create the harvester, providing a wide range of options for reasonably priced and environmentally friendly fabrications. “You could imagine harvesters made of one kind of material for rainforest environments, and another for more arid regions.”
Furthermore, because humidity is a constant, the harvester would operate rain or shine, at night, and with or without wind, which eliminates one of the main issues with technologies like solar or wind power, which are only functional in specific environments.
Lastly, thousands of Air-gen devices can be stacked on top of one another to efficiently scale up the amount of energy without expanding the device’s footprint because air humidity diffuses in three dimensions and its thickness is only a small portion of a human hair’s width. A device like this would be able to provide power at the kilowatt level for use in the general electrical utility.
“Imagine a future world in which clean electricity is available anywhere you go,” Yao says. “The generic Air-gen effect means that this future world can become a reality.”