Microbial Battery Uses Fungi To Power Off-Grid Electronics

What if, instead of taking traditional batteries out into the wild to power remote sensors, you could bring a non-toxic “living” biobattery instead?

In a new paper, published in ACS Sustainable Chemistry & Engineering, researchers at the Swiss Federal Laboratories for Materials Science and Technology (Empa) report the development of a first-of-its-kind, 3D-printed cellulose-based fungal biobattery.

Using a combination of yeast and white-rot fungus, mixed in with a cellulose hydrogel, the team was able to synthesize electronically conductive 3D-printable inks for use as electrodes. Their proof-of-concept biobattery is constructed using these fungal inks, beeswax and a cellulose proton exchange membrane to form a fully biodegradable device.

Such devices could be used as an alternative for powering agricultural or environmental sensors in rural locations, the researchers say, as their biodegradable nature means they will not contribute to the rising levels of e-waste.

The fungal battery

In technical terms, this fungal battery isn’t a battery at all, but a device known as a microbial fuel cell (MFC).

MFCs use the metabolism of living things — traditionally bacteria or algae — to convert nutrients into energy. For this new cell, the researchers chose to investigate an MFC design that would rely on the yeast Saccharomyces cerevisiae (also known as brewer’s yeast) and the white-rot fungus Trametes pubescens as its active microorganisms.

“The use of fungi to make microbial fuel cells appeared to be a more novel approach. In particular, the use of white-rot fungi, ” Dr. Carolina Reyes, first author of the new study told Technology Networks. “Not too many fungal MFCs have been made compared to bacterial MFCs, for example.”

These two species of fungi work synergistically within the MFC; when the yeast is exposed to nutrients it releases electrons, while the white-rot fungus produces an enzyme that can use those electrons to reduce oxygen.

“On one side of the MFC, called the anode, the microorganism produces electrons (tiny charged particles) from the breakdown of nutrients, like sugars,” Reyes explained. “Those electrons travel to the other side of the MFC, called a cathode, through an external wire, creating electricity as a result of this movement of electrons. At the cathode, those electrons combine with oxygen in the air and water, completing the circuit and releasing energy in the process.”

Each electrode is made from a cellulose-based hydrogel that can be 3D printed and mixed with carbon black and graphite nanoflakes to tune their viscosity and enhance their electrical conductivity.

To turn these fungal hydrogel electrodes into a fully functional proof-of-concept device, the researchers designed additional MFC parts using beeswax and a custom cellulose proton exchange membrane to keep the device fully biodegradable.

Towards off-grid, sustainable electronics

These fungal batteries can produce between 300 and 600 mV for several days and can be connected in parallel. During testing, four fungal batteries connected in parallel were able to power a small temperature sensor for 65 hours.

Another perk of the batteries is that the fungi can survive in a dried state within the hydrogel inks, meaning they are easy to transport to remote locations and re-activate by simply adding water and a nutrient source, such as a simple sugar mix.

While the fungi can survive during periods of being dried out, working with living material proved to be a challenge for the researchers during the initial MFC development stages.

“One major challenge we faced was figuring out how to mix the fungi into the cellulose and carbon black conductive inks while still keeping them alive,” Reyes recalled. “We used a lot of mechanical mixing steps that were quite harsh on the fungi. However, the fungi we selected were quite robust and could remain alive even after these steps.”

Having now created a fully biodegradable fungal MFC powerful enough to power small sensors, the researchers now plan to investigate different kinds of fungi that might result in fungal batteries that are even more powerful and longer-lasting. Ultimately, a powerful fungal battery could become a useful tool for researchers or agricultural workers operating in highly remote locations.

“Fungal-based fuel cells could potentially be used in field applications (off the energy grid) for powering small sensors that record temperature and humidity,” Reyes said.

“We envision their use in agricultural fields and in forests, for example. In the future, we could potentially integrate fungal-based fuel cells to power low-power microcomputers, soft robots, microcontrollers, machine learning and even to power low-power devices destined for space exploration.”

Reference: Reyes C, Fivaz E, Sajó Z, et al. 3D printed cellulose-based fungal battery. ACS Sustain Chem Eng. 2024;12(43):16001-16011. doi: 10.1021/acssuschemeng.4c05494