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Electrical engineer Jun Yao and microbiologist Derek Loveley, working at the University of Massachusetts Amherst, have described, in a recent paper in Nature, a bioelectrical device capable of producing clean electricity from nothing more than slightly moist air.
The device in question they have named the Air-gen. It consists of a film of electrically conducting protein nanowires, 7 microns thick, a fraction of the width of a human hair. One side of the film sits on an electrode, while a smaller gold electrode covers part of the film’s top face. When the air around the device contains water, as air very often does, it is absorbed by the film, setting up conditions that cause an electrical current to flow between the two electrodes. All that is required to keep the current flowing is continuous air moisture.
They describe in their paper how “…existing moisture-based energy-harvesting technologies can produce only intermittent, brief (shorter than 50 seconds) bursts of power in the ambient environment, owing to the lack of a sustained conversion mechanism”.
Some of these existing technologies, they explain, even require constant contact with liquid water in order to function. Whereas the Air-gen, which they claim is simpler and more robust, and cheaper to make, can reliably provide power for up to twenty hours, using atmospheric humidity alone, before self-recharging.
Yao and Loveley describe how their Air-gen cell delivered a potential difference of 0.5 Volts across the 7-micron thick film, and a current density of around 17 micro-amperes per square centimetre. Air-gen cells can be connected together to increase the power to levels capable of running electrical devices. It also works equally well in the dark, or indoors, as long a little atmospheric humidity is present. The amount required is low enough that Air-gen, amazingly enough, could even work in areas known for their low humidity, such as the Sahara desert. The Air-gen, the team hope, could one day make traditional batteries for our devices a thing of the past.
But where does the magical protein nanowire substance come from? The perhaps unexpected answer to that is a bacteria named Geobacter sulfurreducens. Geobacter is also known as “electricigens” due to its ability to produce electricity. Loveley has worked for decades with this microbe and his lab discovered its ability to make the conductive protein nanowires. He and Yao joined forces to see if electronic devices could be made using these nanowires, and the result of this collaboration is the Air-gen.
In Science Daily, Yao says, “The ultimate goal is to make large-scale systems. For example, the technology might be incorporated into wall paint that could help power your home. Or, we may develop stand-alone air-powered generators that supply electricity off the grid. Once we get to an industrial scale for wire production, I fully expect that we can make large systems that will make a major contribution to sustainable energy production.”
Air-gen looks like a very exciting addition to our sustainable energy options. Perhaps, in a few decades from now, the concept of finding a power outlet to charge a device might be as outdated as the rotary phone, thanks to our smallest of friends, the bacteria.
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