A group of engineers from the University of Massachusetts Amherst has demonstrated that almost any material can be transformed into a device that constantly harvests electricity from humidity in the air. The key is to be able to pepper the material with nanopores no larger than 100 nanometers in diameter. The findings were published in the journal Advanced Materials.
The secret to making electricity from thin air? Nanopores. Image Credit: Derek Lovley/Ella Maru Studio
“This is very exciting. We are opening up a wide door for harvesting clean electricity from thin air,” says Xiaomeng Liu, a Graduate Student in electrical and computer engineering at UMass Amherst’s College of Engineering and the paper’s lead author.
The air contains an enormous amount of electricity. 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 that we can harvest it.
Jun Yao, Study Senior Author and Assistant Professor, Electrical and Computer Engineering, College of Engineering, University of Massachusetts Amherst
The heart of the man-made cloud is based on what Yao and his coworkers refer to as the "generic Air-gen effect," and it expands on work completed in 2020 by Yao and co-author Derek Lovley, Distinguished Professor of Microbiology at UMass Amherst, revealing that electricity could be consistently harvested from the air using a specialized material made of protein nanowires grown from the bacterium Geobacter sulfurreducens.
What we realized after making the Geobacter discovery,” says Yao, “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 property? “It needs to have holes smaller than 100 nanometers (nm), or less than a thousandth of the width of a human hair.
Jun Yao, Study Senior Author and Assistant Professor, Electrical and Computer Engineering, College of Engineering, University of Massachusetts Amherst
This is due to a characteristic known as the “mean free path,” which is the distance traveled by a single molecule of material, in this case, water in the air, before colliding with another single molecule of the same substance. Water molecules suspended in the air have a mean free path of roughly 100 nm.
Yao and his co-workers discovered they could build an electricity harvester around this number. This harvester would be comprised of a thin layer of material having nanopores less than 100 nm in size that would allow water molecules to move from the upper to the lower part of the material.
However, because each pore is so small, water molecules passing through the thin layer would easily collide with the pore’s edge. This means that the upper half of the layer would be bombarded with far more charge-carrying water molecules than the lower section, resulting in a charge imbalance similar to that seen in clouds as the higher part increased its charge relative to the lower part. This would effectively construct a battery—one that runs on electricity.
The idea is simple, but it’s never been discovered before, and it opens all kinds of possibilities.
Jun Yao, Study Senior Author and Assistant Professor, Electrical and Computer Engineering, College of Engineering, University of Massachusetts Amherst
The harvester might be made of virtually any material, providing a wide range of options for cost-effective and environmentally friendly fabrications.
“You could image harvesters made of one kind of material for rainforest environments, and another for more arid regions,” Jun Yao stated.
And, because the humidity is always present, the harvester would run 24 hours a day, seven days a week, rain or shine, even at night, wind or no wind, resolving one of the fundamental issues with technologies like wind or solar, which only work under particular conditions.
Furthermore, since air humidity diffuses in three dimensions and the thickness of the Air-gen device is only a fraction of the width of a human hair, thousands of them can be layered on top of each other, thereby scaling up the quantity of energy while reducing the device’s footprint. An Air-gen device of this type might provide kilowatt-level power for ordinary electrical utility usage.
Yao concludes, “Imagine a future world in which clean electricity is available anywhere you go. The generic Air-gen effect means that this future world can become a reality.”
The National Science Foundation, Sony Group, Link Foundation, and the Institute for Applied Life Sciences (IALS) at UMass Amherst funded this research, which combines deep and interdisciplinary expertise from 29 departments on the UMass Amherst campus to translate fundamental research into advancements that support human health and well-being.
Journal Reference
Liu, X., et al. (2023). Generic Air‐gen Effect in Nanoporous Materials for Sustainable Energy Harvesting from Air Humidity. Advanced Materials. doi.org/10.1002/adma.202300748.