The engineers demonstrated something wonderful. Almost any material can be used to create a device that continuously harvests energy from moist air.
It is not a ready-made development for practical application, but, say its creators, it transcends some of the limitations of other harvesters. All the material needs is to be pierced with nanopores less than 100 nanometers in diameter. That’s about one-thousandth the width of a human hair, so easier said than done, but a lot simpler than you’d expect.
This material can collect the electricity generated by microscopic droplets of water in humid air, according to a team led by engineer Xiaomeng Liu of the University of Massachusetts Amherst.
They called their finding the “generic air generation effect”.
“Air contains an enormous amount of electricity,” says UMass Amherst engineer Jun Yao.
“Think of a cloud, which is nothing more than a mass of water droplets. Each of these droplets contains a charge, and when conditions are right, the cloud can produce lightning – but we don’t know how to reliably capture electricity . of lightning. What we’ve done is create a small-scale, man-made cloud that produces electricity for us on a predictable and continuous basis so that we can harvest it.”
If the Air-gen sounds familiar, it’s because the team previously developed an air-energy harvester. However, his previous device relied on protein nanowires grown by a bacteria called geobacter sulfurreducens.
Well, it turns out, the bacteria is not needed.
“What we realized after doing the geobacter The finding is that the ability to generate electricity from air – what we then call the ‘air generation effect’ – turns out to be generic: literally any type of material can harvest electricity from the air, as long as it has a certain property,” Yao explains.
That property is nanopores, and their size is based on the mean free path of water molecules in humid air. This is the distance a water molecule can travel in air before colliding with another water molecule.
The generic Air-gen device is made of a thin film of material such as cellulose, silk protein or graphene oxide. Water molecules in the air can easily enter the nanopores and travel from the top of the film to the bottom, but they run to the sides of the pore as they travel.
These transfers charge the material, producing a buildup, and as more water molecules rush to the top of the film, a charge imbalance occurs between the two sides.
This produces an effect similar to what we see in clouds that produce lightning: rising air creates more collisions between water droplets at the top of a cloud, resulting in excess positive charge in the higher clouds and excess negative charge in the lower ones.
In that case, the charge can be redirected to power small devices or stored in some kind of battery.
At the moment, it is still in the early stages. The cellulose film the team tested had a spontaneous voltage output of 260 millivolts in the environment, whereas a cell phone requires a voltage output of around 5 volts. But the thickness of the films means they can be stacked to scale Air-gen devices to make them more practical in practice.
And the fact that they can be made from different materials means that the devices can be adapted to the environment in which they will be used, the researchers say.
“The idea is simple, but it’s never been discovered before and it opens up all kinds of possibilities,” says Yao. “You could imagine harvesters made from one type of material for rainforest environments and another for more arid regions.”
The next step would be to test the devices in different environments and also work on scaling them. But Airgen’s generic effect is real and the possibilities it represents are hopeful.
“This is very exciting,” says Liu. “We’re opening a wide door to harvesting clean electricity from thin air.”
The research was published in Advanced Materials.