SCIENCE/ENVIRONMENT
A team of engineers at the University of Massachusetts Amherst (UMassA) in the US has discovered that almost any material can be turned into a device that can continuously harvest electricity from humidity in the air.
“This is very exciting,” says Xiaomeng Liu, a graduate student in electrical and computer engineering in the university’s College of Engineering and the paper’s lead author. “We are opening up a wide door for harvesting clean electricity from thin air.”
“The air contains an enormous amount of electricity,” says Jun Yao, assistant professor of electrical and computer engineering, also from the same college and the paper’s senior author. “Think of a cloud, which is nothing more than a mass of water droplets. Each of those droplets contains a charge, and when conditions are right, the cloud can produce a lightning bolt — but we don’t know how to reliably capture electricity from lightning. What we’ve done is to create a human-built, small-scale cloud that produces electricity for us predictably and continuously so we can harvest it.”
The heart of the human-made cloud depends on what Yao and his colleagues call the “generic Air-gen effect”, and it builds on work Yao and co-author Derek Lovley, Distinguished Professor of Microbiology at UMassA, had previously completed in 2020 showing that electricity could be continuously harvested from the air using a specialised material made of protein nanowires grown from the bacterium Geobacter sulfurreducens.
“What we realised after making the Geobacter discovery, says Yao, "is that the ability to generate electricity from the air turns out to be generic: literally any kind of material can harvest electricity from air, as long as it has a certain property.”
That property? “It needs to have holes smaller than 100 nanometers (nm), or less than a thousandth of the width of a human hair,” Yao notes.
Yao and his colleagues realised they could design an electricity harvester based on this number. This harvester would be made from a thin layer of material filled with nanopores smaller than 100nm that would let water molecules pass from the upper to the lower part of the material. As each pore is so small, the water molecules would easily bump into the pore’s edge as they pass through the thin layer. This means the upper part of the layer would be bombarded with many more charge-carrying water molecules than the lower part, creating a charge imbalance, like that in a cloud, as the upper part increased its charge relative to the lower part. This effectively creates a battery — one that runs as long as there’s any humidity in the air.
“The idea is simple,” says Yao, “but it’s never been discovered before, and it opens all kinds of possibilities.” The harvester could be designed from literally all kinds of material, offering broad choices for cost-effective and environment-adaptable fabrications. “You could imagine harvesters made of one kind of material for rainforest environments, and another for more arid regions.”
And since humidity is ever-present, the harvester would run all the time, rain or shine, at night and whether or not the wind blows, which solves one of the major problems of technologies such as wind or solar, which only work under certain conditions.
Finally, because air humidity diffuses in three-dimensional space and the thickness of the Air-gen device is only a fraction of the width of a human hair, many thousands of them can be stacked on top of each other, efficiently scaling up the amount of energy without increasing the footprint of the device. Such an Air-gen device would be capable of delivering kilowatt-level power for general use.
“Imagine a future world in which clean electricity is available anywhere you go,” says Yao. “The generic Air-gen effect means that this future world can become a reality.”
This research was published in the journal Advanced Materials and was supported by the National Science Foundation, Sony Group, Link Foundation, and also the Institute for Applied Life Sciences (IALS) at UMassA, which brings together expertise from 29 university departments to translate fundamental research into innovations that benefit human health and wellbeing.