In May, a team at the University of Massachusetts (UMass) Amherst published a paper declaring they had successfully generated a small but continuous electric current from humidity in the air. It’s a claim that will probably raise a few eyebrows, and when the team made the discovery that inspired this new research in 2018, it did.
“To be frank, it was an accident,” says the study’s lead author, Prof Jun Yao. “We were actually interested in making a simple sensor for humidity in the air. But for whatever reason, the student who was working on that forgot to plug in the power.”
The UMass Amherst team were surprised to find that the device, which comprised an array of microscopic tubes, or nanowires, was producing an electrical signal regardless.
Each nanowire was less than one-thousandth the diameter of a human hair, wide enough that an airborne water molecule could enter, but so narrow it would bump around inside the tube. Each bump, the team realised, lent the material a small charge, and as the frequency of bumps increased, one end of the tube became differently charged from the other.
“So it’s really like a battery,” says Yao. “You have a positive pull and a negative pull, and when you connect them the charge is going to flow.”
For their recent study, Yao’s team have moved on from nanowires, and instead are punching materials with millions of tiny holes, or nanopores. The device they have come up with is the size of a thumbnail, one-fifth the width of a human hair, and capable of generating roughly one microwatt – enough to light a single pixel on a large LED screen.
So what would it take to power the rest of the screen, or indeed a whole house? “The beauty is that the air is everywhere,” says Yao. “Even though a thin sheet of the device gives out a very tiny amount of electricity or power, in principle, we can stack multiple layers in vertical space to increase the power.”
That’s exactly what another team, Prof Svitlana Lyubchyk and her twin sons, Profs Andriy and Sergiy Lyubchyk, are trying to do. Svitlana Lyubchyk and Andriy are part of the Lisbon-based Catcher project, whose aim is “changing atmospheric humidity into renewable power”, and along with Sergiy they have founded CascataChuva, a startup intended to commercialise the research. They first began working on the idea in 2015, some time before Yao’s team at the UMass Amherst. “We were considered the freaks,” says Andriy. “The guys who were saying something completely impossible.”
In fact, trying to prove the worth of an early proof-of-concept at conferences had them literally red in the face. He says: “The signal was not stable and it was low. We were able to generate 300 milliwatts, but you had to put all your effort into your lungs in order to breathe enough humidity into the samples.”
They’ve come a long way since then, with Catcher and related projects receiving nearly €5.5m (£4.7m) in funding from the European Innovation Council. The result is a thin grey disc measuring 4cm (1.5in) across. According to the Lyubchyks, one of these devices can generate a relatively modest 1.5 volts and 10 milliamps. However, 20,000 of them stacked into a washing machine-sized cube, they say, could generate 10 kilowatt hours of power a day – roughly the consumption of an average UK household. Even more impressive: they plan to have a prototype ready for demonstration in 2024.