Biodegradable Battery Can Supply Power to SensorsBiodegradable Battery Can Supply Power to Sensors

As part of a three-year research project, supported by the Gebert Rüf Stiftung as part of their Microbials funding program, researchers from Empa's (Swiss Federal Laboratories for Materials Science and Technology) Cellulose and Wood Materials laboratory have developed a functioning fungal battery.

The living cells do not produce a whole lot of electricity, but do have enough to power a temperature sensor for several days, for example. Such sensors are used in agriculture or in environmental research and in remote locations. The biggest advantage of the fungal battery is that, unlike conventional batteries, it is not only completely non-toxic but also biodegradable. The battery actually digests itself from the inside when its work is done.

Technically, the cell is not a battery, but a microbial fuel cell. Like all living things, microorganisms convert nutrients into energy. Microbial fuel cells make use of this metabolism and capture part of the energy as electricity. Until now, they have mostly been powered by bacteria.

"For the first time, we have combined two types of fungi to create a functioning fuel cell," says Carolina Reyes, an Empa researcher. The metabolisms of the two species of fungi complement each other: On the anode side, there is a yeast fungus whose metabolism releases electrons. And the cathode is colonized by a white rot fungus, which produces a special enzyme that allows the electrons to be captured and conducted out of the cell.

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The components of the fungal battery are manufactured using 3D printing. This allows the researchers to structure the electrodes in such a way that the microorganisms can access the nutrients as easily as possible. To do this, the fungal cells are mixed into the printing ink.

"It is challenging enough to find a material in which the fungi grow well," said Gustav Nyström, head of the Cellulose and Wood Materials lab. "But the ink also has to be easy to extrude without killing the cells – and of course we want it to be electrically conductive and biodegradable."

The grid printed electrode contains the fungus used in the anode compartment of the battery. Image: Empa

The researchers produced a suitable ink based on cellulose. The fungal cells can use the cellulose as a nutrient which can help to break down the battery after use. However, their preferred nutrient source is simple sugars, which are added to the battery cells. "You can store the fungal batteries in a dried state and activate them on location by simply adding water and nutrients," said Reyes.

Although the fungi survive such dry phases, working with the living materials posed a number of challenges for the researchers. The interdisciplinary project combines microbiology, materials science, and electrical engineering. In order to characterize the fungal batteries, trained microbiologist Reyes not only had to learn electrochemistry techniques, but also to adapt them to 3D-printing inks.

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The researchers now plan to make the fungal battery more powerful and longer-lasting — and to look for other kinds of fungi that would be suitable for supplying electricity. Both Reyes Nyström agree that fungi are still under-researched and under-utilized, especially in materials science.