Northwestern University researchers have introduced a soil microbial fuel cell that significantly outperforms similar technologies and provides a sustainable solution for powering low-energy devices with full public access to its designs for widespread application. The 3D-printed cover of the fuel cell looks up from the ground. The cover keeps debris away from the device while providing airflow. Credit: Bill Yen/Northwestern University
A team of researchers led by Northwestern University has developed a new fuel cell that harvests energy from microbes living in dirt.
About the size of a standard paper notebook, the all-soil-powered technology could fuel underground sensors used in precision agriculture and green infrastructure. It could potentially offer a sustainable, renewable alternative to batteries that store toxic, flammable chemicals that leak into the ground, are riddled with conflict-ridden supply chains and contribute to the ever-growing e-waste problem.
To test the new fuel cell, the researchers used it to power sensors that measure soil moisture and detect touch, which could be valuable for tracking passing animals. To enable wireless communication, the researchers also equipped the ground-based sensor with a small antenna to reflect existing radio frequency signals and transmit data to a neighboring base station.
Not only did the fuel cell work in both wet and dry conditions, but its power exceeded similar technologies by 120%.
The research will be published today (Jan. 12) in the Proceedings of the Association for Computing Machinery on Interactive, Mobile, Wearable, and Ubiquitous Technologies. The study authors also make all designs, tutorials, and simulation tools available to the public so that others can use and build on the research.
“The number of devices in the Internet of Things (IoT) is constantly increasing,” said Northwestern graduate Bill Yen, who led the work. “If we envision a future with trillions of these devices, we can’t 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 a small amount of energy to power a network of decentralized devices. In search of a solution, we looked at soil microbial fuel cells, which use special microbes to break down soil and use this small amount of energy to power sensors. As long as there is organic carbon in the soil for microbes to break down, the fuel cell could potentially last forever.”
Bill Yen, lead author of the study, buried the fuel cell during testing in a laboratory at Northwestern University. Credit: Northwestern University
“These microbes are everywhere; they already live on land everywhere,” said Northwestern’s George Wells, lead author of the study. “We can use very simple engineering systems to capture their electricity. We are not going to power all cities with this energy. But we can harvest small amounts of energy to support practical, low-power applications.”
Wells is an associate professor of civil and environmental engineering at Northwestern’s McCormick Engineering School. Now a Ph.D. Yen, a student at Stanford University, started the project while an undergraduate researcher in the Wells lab.
Solutions for dirty work
In recent years, farmers around the world have increasingly adopted precision agriculture as a strategy to increase productivity. The technology-based approach relies on measuring precise levels of soil moisture, nutrients and pollutants to make decisions that improve crop health. This requires a widespread, dispersed network of electronic devices to continuously collect environmental data.
“If you want to run a sensor in nature, on a farm or in a wetland, you have to put a battery in it or collect solar energy,” Yen said. “Solar panels don’t work well in dirty environments because they get covered in dirt, don’t work when there’s no sun, and take up a lot of space. Batteries are also difficult because they run out of power. Farmers are not going to regularly walk around a 100-acre farm to change batteries or dust off solar panels.
To overcome these challenges, Wells, Yen and their collaborators wondered if they could instead harvest energy from the existing environment. “We can harvest energy from land that farmers track anyway,” Yen said.
‘Natural Endeavors’
First seen in 1911, soil-based microbial fuel cells (MFCs) work like batteries with an anode, cathode, and electrolyte. But instead of using chemicals to generate electricity, MFCs harvest electricity from bacteria that naturally donate electrons to nearby conductors. When these electrons flow from the anode to the cathode, they create an electrical circuit.
The fuel cell was covered in dirt after it was removed from the ground for work. Credit: Bill Yen/Northwestern University
But in order for microbial fuel cells to function properly, they need to be moist and rich in oxygen – something that’s difficult when buried underground in dry dirt.
“Although MFCs have existed as a concept for more than a century, their unreliable performance and low output power have hindered efforts to make practical use of them, especially under low humidity conditions,” Yen said.
Winning geometry
With these challenges in mind, Yen and his team embarked on a two-year journey to develop a practical, reliable soil-based MFC. His expedition included creating and comparing four different versions. First, the researchers collected nine months of aggregate data on the performance of each design. Next, they tested their final version in an outdoor garden.
The best performing prototype performed well in both dry and wet conditions. The secret of its success: Geometry. Instead of using the traditional design where the anode and cathode are parallel to each other, the winning fuel cell used a perpendicular design.
An anode made of carbon felt (a cheap, abundant conductor to trap the microbes’ electrons) is horizontal to the earth’s surface. A cathode made of an inert, conductive metal sits vertically above the anode.
Although the entire device is buried, the vertical design ensures that the top end is flush with the surface of the ground. A 3D printed lid rests on top of the device to prevent debris from falling inside. A hole at the top and an empty air chamber running alongside the cathode provide consistent air flow.
The lower end of the cathode remains embedded deep below the surface, allowing it to absorb moisture from the moist, surrounding soil—even when the surface soil dries out in sunlight. The researchers also covered part of the cathode with a waterproofing material so that it could breathe during flooding. After potential flooding, the vertical design allows the cathode to dry gradually rather than all at once.
On average, the resulting fuel cell produced 68 times more energy than needed to drive the sensors. It was also quite robust to large changes in soil moisture—from slightly dry (41% water by volume) to completely submerged.
Making computing accessible
The researchers say that all the components for their soil-based MFC can be purchased at a local hardware store. Next, they plan to develop a soil-based MFC made entirely of biodegradable materials. Both designs bypass complex supply chains and avoid using conflict minerals.
“With COVID-19 “With the pandemic, we’ve all learned how a crisis can disrupt the global supply chain for electronics,” said study co-author Josiah Hester, a former Northwestern faculty member now at the Georgia Institute of Technology. we want to build devices that use it.”
Reference: “Ground Computing” by Bill Yen, Laura Jaliff, Louis Gutierrez, Philothei Sahinidis, Sadie Bernstein, John Madden, Stephen Taylor, Colleen Josephson, Pat Pannuto, Weitao Shuai, George Wells, Nivedita Arora, and Josiah Hester, 11 January 2024 , Proceedings of the ACM on Interactive, Mobile, Wearable, and Ubiquitous Technologies.
DOI: 10.1145/3631410
The research was supported by the National Science Foundation (award number CNS-2038853), the Agriculture and Food Research Initiative from the USDA National Institute of Food and Agriculture (award number 2023-67021-40628), the Alfred P. Sloan Foundation, VMware. Research and 3M.