Researchers at Northwestern University have unveiled a fuel cell powered by soil microbes that significantly outperforms similar technologies and provides a sustainable solution for powering low-energy devices, and is fully open to the public for its design to be widely used. The 3D-printed lid of the fuel cell is exposed to the ground. The lid prevents debris from entering the device while allowing air circulation. **Bill Yen Northwestern University.
A research team led by Northwestern University has developed a new fuel cell that can harvest energy from microorganisms that live in the soil.
This entirely soil-driven technology is about the size of a standard paperback book and could fuel underground sensors used in precision agriculture and green infrastructure. This has the potential to provide a sustainable, renewable alternative to batteries that contain toxic, flammable chemicals that leach into the ground, fraught with conflict-ridden chains, and contribute to the growing problem of e-waste.
To test the new fuel cell, the researchers used it to power sensors that measure soil moisture and detect the sense of touch, a capability that is valuable for tracking animals as they pass. To enable wireless communication, the researchers also equipped the soil-powered sensors with a tiny antenna that transmits data to a nearby base station by reflecting existing RF signals.
Not only do fuel cells work in both wet and dry conditions, but they also deliver 120% more power than comparable technologies.
The research will be published today (12 January) in the Interactive, Mobile, Wearable, and Everywhere Technology Computer Society Collection. The authors of the study also released all the designs, tutorials, and tools to the public so that others could use and build the studies.
The number of devices in the Internet of Things (IoT) is growing," said Bill Yen, an Northwestern alumnus who led the effort. "If we imagine trillions of such devices in the future, we can't make every single one of them out of lithium, heavy metals, and toxins that are harmful to the environment. We need to find alternatives that can provide low energy to power a distributed network of devices. In our search for a solution, we looked at soil microbial fuel cells, which use special microorganisms to break down the soil and use a small amount of energy to power the sensors. As long as there is organic carbon in the soil for microorganisms to decompose, fuel cells are likely to last forever.
Bill Yen, the study's lead author, buried fuel cells in tests in a Northwestern University laboratory. **Northwestern University.
These microbes are everywhere; They already live in soil everywhere," said George Wells of Northwestern University, a senior author of the study. "We can use very simple engineering systems to capture their power. We're not going to power an entire city with that energy. But we can capture small amounts of energy to power practical, low-power applications.
Wells is an associate professor of civil and environmental engineering at Northwestern University's McCormick School of Engineering. Yen, now a PhD student at Stanford University, started the project when he was an undergraduate researcher at the Wells Laboratory.
In recent years, farmers around the world have increasingly adopted precision agriculture as a strategy to increase crop yields. This technology-driven approach relies on precisely measuring the levels of moisture, nutrients, and contaminants in the soil to make decisions that enhance crop health. This requires an extensive, decentralized network of electronic devices to continuously collect environmental data.
If you want to put a sensor in the field, on a farm or in a wetland, you're going to have to put a battery in it or collect solar energy," Yen said. "Solar panels don't work well in dirty environments because they're covered in dirt, don't work when the sun isn't out, and take up a lot of space. Batteries are also challenging because they drain their charge. Farmers don't regularly swap batteries or dust solar panels around the 100-acre farm.
To overcome these challenges, Wells, Yen, and their collaborators wanted to know if they could harvest energy from their existing environment. "In any case, we can get energy from the soil that farmers are monitoring," Yen said.
Soil-based microbial fuel cells (MFCs) debuted in 1911 and worked like batteries – with an anode, cathode, and electrolyte. However, instead of using chemicals to generate electricity, MFC draws electricity from bacteria that naturally supply electrons to nearby conductors. When these electrons flow from the anode to the cathode, it creates a circuit.
Fuel cells, which are extracted from the ground and covered with dirt for research. **Bill Yen Northwestern University.
However, in order for microbial fuel cells to operate undisturbed, they need to retain moisture and oxygenation – which is tricky when buried in dry soil underground.
Although MFCs have been around as a concept for more than a century, their unreliable performance and low output power have hindered their practical use, especially in low humidity conditions," Yen said.
With these challenges in mind, Yen and his team embarked on a two-year journey to develop a practical, reliable soil MFC. His expedition consisted of creating and comparing four different versions. First, the researchers collected nine months of data on the performance of each design. They then tested their final version in an outdoor garden.
The best-performing prototypes work well in dry conditions and standing water. The secret behind its success: its geometry. Instead of using the traditional design where the anode and cathode are parallel to each other, the winning fuel cell has a vertical design.
The anode is made of carbon felt (an inexpensive, abundant conductor that traps the electrons of microorganisms) and is at ground level. The cathode is made of an inert conductive metal and is located perpendicular to the top of the anode.
Although the entire unit is buried underground, the vertical design ensures that the top end is flush with the ground. The 3D-printed lid is placed on top of the device to prevent debris from falling inside. The bore at the top and the air chamber running along the cathode allow for consistent airflow.
The lower end of the cathode remains deeply embedded beneath the surface, ensuring that it retains moisture from the moist surrounding soil – even if the surface soil dries out in the sun. The researchers also coated a portion of the cathode with waterproof material to allow it to breathe during flooding. And, after a potential flood, the vertical design allows the cathode to dry out gradually, rather than all at once.
On average, the resulting fuel cell produces 68 times more power than is needed to run its sensors. It's also sturdy enough to withstand huge variations in soil moisture – from a little dry (41% by volume) to completely underwater.
The researchers say all the components of their soil-based MFC are available at local hardware stores. Next, they plan to develop a soil-based MFC made from a fully biodegradable material. Both designs bypass the complex ** chain and avoid the use of conflict minerals.
With the COVID-19 pandemic, we're all familiar with how the crisis has disrupted the global electronics** chain," said Josiah Hester, a co-author of the study and a former Northwestern University faculty member now at Georgia Tech. "We want to build devices that use local ** chains and low-cost materials so that computing is available to all communities.