They found it on the muddy banks of the Potomac River more than three decades ago: a strange 'sedimentary organism' that could do things that no one ever expected from bacteria.
This unusual microbe, belonging to the Geobacter genus, was known for its ability to produce magnetite in the absence of oxygen, but over time, scientists discovered that it could create other things, such as bacterial nanowires that conduct electricity.
For years, researchers have tried to find ways to make good use of this natural gift, and this year they unveiled a device they call the Air-gen. According to the team, their device can create electricity from … well, almost nothing.
“We literally make electricity out of thin air,” said electrical engineer Jun Yao of the University of Massachusetts Amherst in February. 'Air-gen generates clean energy 24 hours a day.'
The claim may sound like an exaggeration, but a recent study by Yao and his team describes how an air-powered generator can only actually generate electricity when there is air around it. This is all thanks to the electrically conductive protein nanowires produced by Geobacter (in this case, G. serreducens).
Air-gen consists of a thin film of protein nanowires, just 7 micrometers thick, sandwiched between two electrodes.
The nanowire film is capable of adsorbing water vapor that exists in the atmosphere, allowing the device to generate a continuous electric current conducted between two electrodes.
Scientists say the charge is created by a moisture gradient that diffuses protons in the nanowire material.
“This charge diffusion is expected to cause a balancing electric field or potential similar to the resting membrane potential in biological systems,” the authors explain in their study.
“A sustained moisture gradient, which is fundamentally different from anything seen in previous systems, explains the continuous output voltage from our nanowire device.”
The discovery was made almost by accident when Yao noticed that the devices he was experimenting with appeared to conduct electricity on their own.
“I saw that when the nanowires were in contact with the electrodes in a certain way, they generated a current,” Yao said.
“I have found that exposure to atmospheric humidity is important and that protein nanowires absorb water, creating a stress gradient.”
Previous studies have shown that hydroelectric power generation is produced using other types of nanomaterials such as graphene, but these attempts have mostly produced only short pulses of electricity lasting only a few seconds.
In contrast, the Air-gen produces about 0.5 V DC with a current of about 17 microamperes per square centimeter.
It's not much power, but the team said that connecting multiple devices could generate enough power to charge small devices like smartphones and other personal electronics – all without wasting and using nothing but ambient humidity (even in such dry regions like the Sahara Desert).
“The ultimate goal is to build large-scale systems,” Yao said, explaining that in dire need this technology could be used to power homes with nanowires embedded in wall paint.
“Once we move to industrial scale wire production, I fully expect that we will be able to create large systems that make a significant contribution to sustainable energy production.”
A related study by co-worker microbiologist Derek Lowley, who first identified the Geobacter microbes back in the 1980s, could help with this: genetically engineering other microbes, such as E. coli, to perform the same trick on a large scale.
“We've turned E. coli into a protein nanowire factory,” Lovli said.
The results are reported in Nature.
Sources: Photo: (UMass Amherst / Yao and Lovley labs / Ella Maru Studio)
