Fungi are a source of attention. This kingdom of life – more closely related to animals than to plants – encompasses an enormous variety. Everything might be found here: from edible mushrooms to molds, from single-celled life to the most important organisms on Earth, from disease-causing pathogens to drug-making superheroes. Now, researchers at Empa have developed one other potential for fungi: generating electricity.
As a part of a three-year research project, supported by the Gebert Rüf Stiftung as a part of their Microbes funding program, researchers at Empa's Cellulose and Wood Materials Laboratory have developed a functional fungal battery. Living cells don't generate electricity in any respect — but enough to power a temperature sensor for several days, for instance. Such sensors are utilized in agriculture or environmental research. The biggest advantage of the fungal battery: Unlike conventional batteries, it is just not only completely non-toxic but in addition biodegradable.
Mold from the printer
Strictly speaking, the cell is just not a battery, but a so-called microbial fuel cell. Like all organisms, microorganisms convert nutrients into energy. Microbial fuel cells use this metabolism and capture a part of the energy as electricity. So far, they've been powered mostly by bacteria. “For the first time, we have combined two types of fungi to create a working fuel cell,” says Empa researcher Carolina Reyes. The metabolisms of the 2 species of fungi complement one another: on the anode side is a yeast fungus whose metabolism releases electrons. The cathode is colonized by a white-rot fungus, which produces a special enzyme that captures electrons and transports them out of the cell.
The mold is just not “planted” into the battery but is an integral a part of the cell from the beginning. 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 easily access the nutrients. To do that, fungal cells are mixed with printing ink. “It's quite difficult to find a material in which fungi can grow well,” says Gustav Nyström, head of the Cellulose and Wood Materials Laboratory. “But the ink also has to be easy to get out without killing the cells — and of course we want it to be electrically conductive and biodegradable.”
Microbiology meets electrical engineering.
Thanks to their laboratory's extensive experience in 3D printing soft, bio-based materials, the researchers were capable of develop an acceptable cellulose-based ink. Fungal cells also can use cellulose as a nutrient and thus help break down the battery after use. However, their preferred food source is straightforward sugar, which is added to battery cells. “You can store fungal batteries in a dry state and activate them in situ by just adding water and nutrients,” says Rais.
Although robust fungi survive such dry stages, working with living material presented several challenges for researchers. The interdisciplinary project combines microbiology, materials science and electrical engineering. To characterize the fungal batteries, Reiss, a trained microbiologist, needed to learn not only electrochemistry techniques, but in addition adapt them to 3D printing ink.
The researchers now plan to make the fungal battery more powerful and long-lasting — and find other kinds of fungi suitable for power supply. Reyes and Nystrom agree.