They found it buried in the muddy shores of the Potomac River more than three decades ago: a strange “sediment organism” that could do things nobody had ever seen before in bacteria.
This unusual microbe, belonging to the Geobacter genus, was first noted for its ability to produce magnetite in the absence of oxygen, but with time scientists found it could make other things too, like bacterial nanowires that conduct electricity. For years, researchers have been trying to figure out ways to usefully exploit that natural gift, and this year they might have hit pay-dirt with a device they’re calling the Air-gen.
According to the team, their device can create electricity out of… well, almost nothing. “We are literally making electricity out of thin air,” said electrical engineer Jun Yao from the University of Massachusetts Amherst back in February.
“The Air-gen generates clean energy 24/7.” The claim may sound like an overstatement, but a recent study by Yao and his team describes how the air-powered generator can indeed create electricity with nothing but the presence of air around it. It’s all thanks to the electrically conductive protein nanowires produced by Geobacter (G. sulfurreducens, in this instance). The Air-gen consists of a thin film of the protein nanowires measuring just 7 micrometres thick, positioned between two electrodes, but also exposed to the air.
Because of that exposure, the nanowire film is able to adsorb water vapour that exists in the atmosphere, enabling the device to generate a continuous electrical current conducted between the two electrodes. The team said the charge is likely created by a moisture gradient that creates a diffusion of protons in the nanowire material.
“This charge diffusion is expected to induce a counterbalancing electrical field or potential analogous to the resting membrane potential in biological systems,” the authors explained in their study. “A maintained moisture gradient, which is fundamentally different to anything seen in previous systems, explains the continuous voltage output from our nanowire device.” The discovery was made almost by accident, when Yao noticed devices he was experimenting with were conducting electricity seemingly all by themselves. “I saw that when the nanowires were contacted with electrodes in a specific way the devices generated a current,” Yao said.
“I found that exposure to atmospheric humidity was essential and that protein nanowires adsorbed water, producing a voltage gradient across the device.” Previous research has demonstrated hydrovoltaic power generation using other kinds of nanomaterials – such as graphene – but those attempts have largely produced only short bursts of electricity, lasting perhaps only seconds.
