Scientists have created a cloud device that can harvest clean electricity from the humidity in air, an academic paper reveals.
The fingernail-sized contraption, called Air-gen, is made from a material filled with holes less than a thousandth of the width of a human hair.
The holes, called nanopores, make clean power by harvesting the energy from electrically charged water in the air that passes through them.
Essentially, the device harnesses the power in clouds that make lightning.
'Human-built, small-scale cloud'
Dr Jun Yao, the senior author from Massachusetts University in the US, said: “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."
The technique can be scaled up for use in numerous different environments, from an Amazon rainforest to the Sahara Desert.
Clean energy everywhere
Dr Yao added: "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."
Three years ago the same team showed how electricity could be continuously harvested from the air using a specialised material made of protein nanowires grown from the bacterium Geobacter sulfurreducens.
Graduate student Xiaomeng Liu, lead author of the latest study, which has been published in Advanced Materials, said: "This is very exciting. We are opening up a wide door for harvesting clean electricity from thin air."
They said the breakthrough could be used to tackle the climate emergency by bringing widespread commercialisation of electric vehicles a step closer.
Harvesting electricity from the air
Dr Yao said: "What we realised after making the Geobacter discovery is 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.
"It just needs to have holes smaller than 100 nm (nanometers) - or less than a thousandth of the width of a human hair.”
This is because of a parameter known as the "mean free path" - the distance a single molecule of water travels in air before it bumps into another.
The researchers found they could design an electricity harvester based around this number made from a thin layer of material filled with nanopores smaller than 100nm.
They would let water molecules pass from the upper to the lower part of the material.
Each pore is so small they would easily bump into the edge as they pass through - meaning the upper part would be bombarded with many more charge-carrying water molecules than the lower.
It creates a charge imbalance, like those found in a cloud, as the upper part increased its charge relative to the lower part, creating a battery.
Dr Yao said: "The idea is simple but it's never been discovered before - and it opens all kinds of possibilities."