Energy from thin air
Engineers and microbiologists have collaborated to invent a device that generates electricity out of - literally - thin air. They call this incredible bit of tech, published in Nature, the Air-gen, and it relies on tiny strands of protein farmed from bacteria. These so-called ‘protein nanowires’ absorb trace amounts of humidity in the air and produce electricity. At the moment, the Air-gen can power only small electronic devices, but its inventors, from the University of Massachusetts Amherst, have big plans to scale it up. Phil Sansom spoke to one of them, Derek Lovley, to find out how it works...
Derek - We've developed a new type of sustainable electricity production. We don't require sunlight, we don't require wind. We can make power 24/7 from the humidity in air.
Phil - I've got to be honest, it sounds like science fiction.
Derek - I know. And that was our initial thought too! And we spent many months trying to discredit the idea, but it all checks out and remarkably we can make electricity literally from thin air.
Phil - So how does it work?
Derek - It's a very simple device with two electrodes and a new type of electronic material called protein nanowires. And those wires absorb moisture from the air and generate a voltage and current.
Phil - What am I picturing here? Are there two bits of metal and then something in between them?
Derek - That's correct. Basically a sandwich with the protein nanowires in between two electrodes.
Phil - What is a protein nanowire?
Derek - It is a filament, three nanometers in diameter, 10 to 20 microns long, comprised of protein that we produce with a microorganism called Geobacter. Geobacter is a common constituent of soils and sediments. It produces those wires to make electrical connections with its environment.
Phil - So it's little molecules that are around the edge of this bacteria?
Derek - Little molecules produced inside the bacteria. It assembles them into the wire and as the wire is produced, it pushes it out of the cell. So the cell looks hairy, basically. It has hairs extending all from it. Those are the protein nano wires.
Phil - Are you farming these bacteria and then shaving them like sheep?
Derek - Absolutely. That's exactly what we're doing.
Phil - How physically do you deal with them? Because they must be too small to tweezer off, right?
Derek - Absolutely. But it's quite a simple process. We throw them into a blender, which will sheer the wires off of the cell and then we collect the wires on a filter.
Phil - And so how many do you get at once?
Derek - Billions and billions, but of course they're so small it's only micrograms from a relatively large number of microbes.
Phil - Wow. And then do you attach them to the metal?
Derek - Actually, we just suspend them in water, put a drop of that water on the electrode and let the water dry off.
Phil - Once you've done that, what's the point of all this? What are they doing once they're actually on the electrode?
Derek - They start making electricity. I mean, and this was a very surprising result to us, we were actually working with the protein nanowires to make wearable electronic sensors. And then even without applying any electricity to the system, it was generating electricity itself.
Phil - Oh, this was almost an accidental discovery?
Derek - Absolutely serendipitous.
Phil - So do you know how it works then?
Derek - We think we know! As long as it works, right? Okay. Of course we certainly are trying to uncover more of the basic mechanisms and what we do know so far is that a film of the protein wires absorbs moisture from the atmosphere and creates a gradient of water because only the top is exposed to the atmosphere.
Phil - And then how does that water then translate into electric charge?
Derek - The protein nanowires have charges associated with them and are exchanging protons. So it's basically setting up a gradient of protons within that film.
Phil - So is the cool part how tiny these wires are, or is it the way that the charges work on the wires themselves?
Derek - I think it's both. You need to have tiny wires with tiny pores in between the wires. But they also have to have this charge in order to get the voltage gradient.
Phil - And how much electricity can you actually get out?
Derek - Right now, we're making small amounts of power and the reason for that is the initial devices were quite small. This was because we could not produce a large quantity of wires with Geobacter. We've now constructed a new microbe, a strain of E-Coli, which is very easy to grow, can be grown in large quantities so we can mass produce the wires.
Phil - And once they're mass produced, what's the potential? How much power can you get out of this?
Derek - Everything that I'm going to say next is theoretical because we've only made the small devices, but with continued scaling a device, say the size of a refrigerator, could in theory generate enough electrical power to power, say a small home.
Phil - And does it matter if you're in a really, really humid environment? Do you have to be in the rainforest for example?
Derek - No, that is another fantastic part of this process. It can work over a wide range of humidity, say even as low as you would find in the Sahara desert.