How harvesting electricity from humid air could one day power our devices

In 2020, Yao and his colleagues published a scientific paper that described how tiny protein nanowires, produced by a bacterium, could harvest electricity from the air. The exact mechanism is still under discussion, but the material’s tiny pores appeared to be able to trap floating water molecules. As they rub against the material, the water molecules also appear to lend it a charge.

Yao explains that, in such a system, most molecules stay near the surface and deposit lots of electrical charge while a few others penetrate more deeply. This creates a difference in charge between the upper and lower parts of the material layer.

“Over time, you see that there is charge separation happening,” says Yao. “That’s actually what happens in a cloud.” On a much larger and more dramatic scale, storm clouds also create a build-up of opposing electrical charges that eventually discharge in the form of lightning.

This means that, by influencing the movement of water molecules and creating just the right conditions for charge separation, you can generate electricity. “The device can work literally anywhere on Earth,” says Yao.

That 2020 paper turned out to be the tip of the iceberg.

Yao and his colleagues published a follow-up study in May 2023 where they created the same kind of structure, filled with nanopores, but using a variety of different materials – from graphene oxide flakes and polymers to cellulose nanofibers derived from wood. They all worked, albeit with some small differences. This suggests the structure is what matters, rather than the material itself.

In the experiments so far, devices thinner than a human hair generated very small amounts of electricity, equivalent to a fraction of a volt. Yao suggests that by simply making more material, or linking pieces of it together, you could begin to get useful charges of multiple volts and up. It could even be made from a liquid that could be sprayed onto surfaces to provide an instant power source, he suggests.

“I think it’s really exciting,” says Reshma Rao, a materials engineer at Imperial College London in the UK, who was not involved in the study. “There’s huge flexibility in the kind of materials you can use.”

Nevertheless, it might not be realistic to imagine such technology powering entire buildings or energy-hungry machines like cars, Rao cautions. Humidity might only be enough to power internet-of things-devices, such as sensors, or small wearable electronics.