Microbial fuel cells (MFC) use microorganisms to convert the chemical energy of organic compounds into electricity through microbial metabolism that helps prevent solids from being polluted by flammable chemicals. These green energy technologies, such as soil-based microbial fuel cells, exhibit a wide range of carbon sources, including wastes, and can be utilized by different microbes. As a result, microbial transformation of wastes using new bioremediation strategies such as MFC for energy production is considered an efficient and environmentally friendly approach. 

A team led by Northwestern University in Illinois has developed a new fuel cell they say can harvest energy from soil-dwelling microbes. The fuel is the size of a book and could potentially be used to power underground sensors used in green infrastructure and precision agriculture. It could become a sustainable, renewable alternative to batteries that use toxic and flammable chemicals that could leak into the ground when used in soil. Materials used to make batteries also pass through conflict-affected supply chains and contribute to e-waste.

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 the Proceedings of the Association for Computing Machinery on Interactive, Mobile, Wearable, and Ubiquitous Technologies. The first option can be used to track passing animals. The researchers also added a small antenna to the ground-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 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 small amounts of energy to power a decentralized network of devices. In our search for a solution, we focused on 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 the microbes to decompose, the fuel cell can potentially last forever,” said Northwestern graduate Bill Yen.

Soil Based Microbial Fuel Cells 

Soil microbial fuel cells (MFCs) are not new. First created in 1911, they work not all that different from batteries. They have an anode, a cathode, and an electrolyte. But instead of using chemicals to generate electricity, they harvest electricity from bacteria that naturally transfer electrons to nearby conductors. These electrons from the anode to the cathode form an electrical circuit.

“Although MFCs have existed as a concept for more than a century, their unreliable performance and low power output have thwarted efforts to make them practical, especially in low humidity conditions,” Yen adds. This is because they need to stay hydrated and oxygenated to function 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 in the dry - its geometry. Instead of using a traditional design in which the anode and cathode are parallel to each other, this design uses a perpendicular design.

"Even when the entire device is buried, the vertical construction ensures that the top end is level with the ground surface. The researchers placed a 3D-printed cap on top of the device to prevent debris from falling. There is also a hole at the top and an empty air chamber running parallel to the cathode for consistent airflow."

Meanwhile, the lower end of the cathode remains seated below the surface, ensuring that it remains hydrated from the moist soil there even as the topsoil dries out in the sunlight. One part of the cathode is coated with a waterproofing material to ensure that it can breathe even in a flood.

The researchers found that this fuel cell design generated 68 times the energy needed to operate the sensors and was also strong enough to withstand large changes in soil moisture. Interestingly, the researchers say that all the components of a soil MFC can be purchased at your local hardware store. In theory, too, if there are microbes and carbon in the solid to break it down first, the battery can run indefinitely.

Agriculture and Green Infrastructure

The new device, about the size of a standard paperback book, relies entirely on soil-powered technology. It uses special microbes to break down the soil and uses this small amount of energy to power the sensors. Underground sensors can then be used in precision agriculture and green infrastructure. This innovation has the potential to provide a sustainable, renewable alternative to batteries that contain toxic, flammable chemicals that could leach into the ground. Conventional batteries are also fraught with conflict-ridden supply chains, contributing to the ever-growing e-waste problem.

Reliable soil microbial fuel cells (MFC) had a unique geometry with a horizontal carbon felt anode and a vertical conductive metal cathode, resulting in a convincing performance in dry and wet conditions. Buried with the top end flush with the ground, the device featured a 3D-printed cap and airflow chamber. The lower end of the cathode remained hydrated due to its depth and was coated with a waterproofing material to function during floods. This fuel cell generated 68 times the energy needed for its sensors and could handle soil moisture from dry to underwater.

Hydrogen Fuel Cell

Dozens of countries have committed to net zero emissions targets in the coming decades. Hydrogen energy is needed to achieve these deep decarbonization goals. It is estimated that electricity alone can hardly reduce 30% of energy-related CO2 emissions, presenting a huge opportunity for hydrogen. The hydrogen economy is advancing in many sectors, including power generation, transport, industrial energy, heat and electricity in buildings, and raw materials. Bloom Energy's solid oxide hydrogen fuel cell technology is uniquely positioned to accelerate the production and use of hydrogen.

Hydrogen is used to power hydrogen fuel cell vehicles. Due to its energy efficiency, a hydrogen fuel cell is two to three times more efficient than a gas-powered internal combustion engine. The refueling time of a fuel cell electric car is less than four minutes on average. Because they can operate independently of the grid, fuel cells can be used in military or disaster areas to act as independent generators of electricity or heat. When fixed in place, they can be connected to the grid and generate consistent, reliable performance.