Biobatteries that need to be fed not charged

Posted: February 21, 2025

Researchers at the Swiss Federal Laboratories for Materials Science and Technology (Empa) have engineered a 3D-printed, biodegradable battery using fungi. Technically, the cell is not a battery but rather a type of microbial fuel cell.

This living battery has the potential to power small devices like temperature sensors used in agriculture or environmental research for several days before naturally decomposing.

What are biobatteries?

Biobatteries are energy storage devices that use biological processes to generate electricity. Unlike conventional batteries that rely on chemical reactions involving metals and synthetic materials, biobatteries utilize the metabolic activities of microorganisms, which convert nutrients into energy, releasing electrons that can be captured to produce an electric current.

There are primarily two types of biobatteries: enzymatic biobatteries and microbial fuel cells. Both enzymes and microorganisms break down organic compounds, such as glucose, releasing electrons.

The advantages of biobatteries include their biodegradability and the use of renewable resources. But challenges, such as limited power output and stability, have historically limited their widespread application.

How Swiss researchers created the first fungal biobattery

Until now, most microbial fuel cells have been powered by bacteria, but there are several disadvantages associated with this method. Bacteria are often less efficient at breaking down complex organic matter than fungi, they have less effective electron transfer mechanisms and need more maintenance. Over time, bacteria can form biofilms on the electrodes, which may block the flow of electrons and hinder the efficiency of the fuel cell. This requires periodic cleaning or replacement of electrodes.

"For the first time, we have combined two types of fungi to create a functioning fuel cell," said Carolina Reyes, one of the researchers involved in the project, to Empa media officers.

The battery comprises an anode and a cathode, each associated with a different fungus. The anode incorporates Saccharomyces cerevisiae, commonly known as baker's yeast. During its metabolic processes, this yeast releases electrons. The cathode contains Trametes pubescens, a type of white rot fungus. This fungus produces enzymes capable of capturing electrons released by the yeast.

To build the battery, the researchers used a 3D-printing technique using an ad-hoc formulated ink. "It is challenging enough to find a material in which the fungi grow well," Gustav Nyström, Head of the Cellulose and Wood Materials lab, told Empa media officers. "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 ink consisted of cellulose, which provided a scaffold and nutrients for the fungi, and makes it biodegradable, carbon black and graphite make it electrically conductive. Sugar molecules in the ink served as an initial food source for the fungi, delaying the degradation of the cellulose structure. The entire assembly was then coated with beeswax to manage moisture levels and equipped with copper contacts to facilitate electron flow.

By adding water, the researchers could initiate the metabolic activities of the fungi, leading to electron release and the generation of an electric current. This design allows the battery to remain dormant in a dried state, ensuring stability during storage. 

Potential applications of fungal batteries

While the current power output of the fungal battery is modest, it is sufficient for low-power applications. One promising area is environmental monitoring, where biodegradable batteries could power sensors that measure temperature, humidity, or soil composition. Data can be gathered through wireless transmission, data logging or short-range communication. After completing their function, these batteries would naturally decompose, eliminating the need for retrieval and disposal.

In agricultural settings, such batteries could be used to monitor crop conditions, providing farmers with real-time data without contributing to electronic waste. The battery's self-decomposing nature ensures it leaves no harmful residues in the soil.

Looking ahead, with further optimization to enhance power output and longevity, fungal batteries could find applications in medical diagnostics, where they might power biodegradable sensors or devices that operate within the human body for a limited time before safely decomposing.