Scientists claim this soil-powered fuel cell can ‘run forever’

The researchers tested the new fuel cell by using it to power sensors that detect touch and measure soil moisture and published the results in Proceedings of the Association for Computing Machinery on Interactive, Mobile, Wearable and Ubiquitous Technologies. The former capability can be used for tracking passing animals. The researchers also added a tiny antenna to the soil-powered sensor to transmit data to a nearby base station by reflecting existing radio frequency signals.

“The number of devices in the Internet of Things (IoT) is constantly growing. If we imagine a future with trillions of these devices, we cannot build every one of them out of lithium, heavy metals and toxins that are dangerous to the environment. We need to find alternatives that can provide low amounts of energy to power a decentralized network of devices. In a search for solutions, we looked to soil microbial fuel cells, which use special microbes to break down soil and use that low amount of energy to power sensors. As long as there is organic carbon in the soil for the microbes to break down, the fuel cell can potentially last forever,” said Northwestern alumnus Bill Yen, who led the work, in a press statement. ‘

Soil-based microbial fuel cells (MFCs) are not new. They were first created in 1911 and they operate not all that differently from a battery. They have an anode, a cathode and electrolyte. But instead of using chemicals to generate electricity, they harvest electricity from bacteria that naturally give out electrons to nearby conductors. These electrons from anode to cathode to create an electric circuit.

“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,” added Yen. This is because they need to stay hydrated and oxygenated to operate without disruption, which is quite difficult in dry dirt.

But the new fuel cell developed by the researchers has a secret ingredient that makes it perform better under dry conditions — its geometry. Instead of using a traditional design in which the anode and the cathode are parallel to one another, this one uses a perpendicular design.

The fuel cell can be seen here. (Northwestern University)

Even when the entire device is buried, the vertical design makes sure that the top end is flush with the surface of the ground. The researchers put a 3D-printed cap on top of the device to stop debris from falling. There is also a hole on the top and an empty air chamber running parallel to the cathode for consistent airflow.

Meanwhile, the lower end of the cathode will remain nestled beneath the surface, and this makes sure that it stays hydrated from the moist soil there even when the top soil dries out in the sunlight. One part of the cathode is coated in waterproofing material to make sure that it can breathe even during a flood.

The researchers found this fuel cell design generated 68 times the power needed to operate the sensors and was also strong enough to withstand large changes in soil moisture. Interestingly, the researchers say all components of the soil-based MFC can be purchased at a local hardware store. Also, theoretically, as long as there are microbes and carbon in the solid for the former to break down, the battery can keep running indefinitely.