“Dirt-powered fuel cell” draws near-limitless energy from soil (Loz Blain, January 16, 2024, New Atlas)
Microbial fuel cells, as they’re called, have been around for more than 100 years. They work a little like a battery, with an anode, cathode and electrolyte – but rather than drawing electricity from chemical sources, they work with bacteria that naturally donate electrons to nearby conductors as they chow down on soil.
The issue thus far has been keeping them supplied with water and oxygen, while being buried in the dirt. “Although MFCs have existed as a concept for more than a century, their unreliable performance and low output power have stymied efforts to make practical use of them, especially in low-moisture conditions,” said UNW alumnus and project lead Bill Yen.
So, the team set about creating several new designs targeted at giving the cells continual access to oxygen and water – and found success with a design shaped like a cartridge sitting vertically on a horizontal disc. The disc-shaped carbon felt anode lies horizontally at the bottom of the device, buried deep in the soil where it can capture electrons as microbes digest dirt.
The conductive metal cathode, meanwhile, sits vertically on top of the anode. The bottom part thus sits deep enough to have access to moisture from the deep soil, while the top sits flush with the surface. A fresh air gap runs down the whole length of the electrode, and a protective cap on top stops dirt and debris from falling in and cutting off the cathode’s access to oxygen. Part of the cathode is also coated with a waterproofing material, so that when it floods, there’s still a hydrophobic section of the cathode in touch with oxygen to keep the fuel cell running.
In testing, this design performed consistently across different soil moisture levels, from completely underwater to “somewhat dry,” with just 41% water by volume in the soil. On average, it generated some 68 times more power than was required to operate its onboard moisture and touch detection systems, and transmit data via a tiny antenna to a nearby base station.