How Paper Batteries Charged by Bacteria Could Power Internet of Things

In the lab, the bacteria-based battery uses respiration to convert the biochemical energy stored in organic matter into biological energy. The process involves a cascade of reactions through a system of electron-carrier biomolecules which transfers electrons to a terminal electron acceptor, an anode.

To create the battery, the research team placed freeze-dried “exoelectrogens” on paper. They explain that exoelectrogens are a type of bacteria that can transfer electrons outside of their cells. The electrons pass through the cell membrane and make contact with external electrodes to power the battery.

To activate the battery, the researchers added water or saliva, both of which revived the bacteria. In the lab, the microbial battery produced a maximum power of 4 µW/cm² and current density of 26 µA/cm², which Choi says are “significantly higher” than previous paper-based microbial batteries. Even so, the power performance is “very low,” limiting their application, at least for now. To be viable for commercial use, the power/current density must be improved by a factor of around 1,000, Choi says.

“The beauty of using paper as a device substrate is that you can simply stack or fold them for serial or parallel connection,” Choi says. Origami techniques may be particularly useful.

As part of his earlier work in 2015, Choi created an origami-inspired battery which folds into a square the size of a matchbook. It used an air-breathing cathode created with nickel sprayed onto one side of a piece of office paper. The total cost of the device was five cents.

The paper battery currently has a shelf life of about four months. Choi says that his latest hybrid paper–polymer biobattery readily decomposes in water.

Choi and his colleagues are not alone is working on paper-based batteries. In 2017, a metal-free and biodegradable redox flow battery for portable single-use applications was described by researchers from Spain, Canada, and the U.S. After their cellulose-based battery operated for 100 minutes, it was disposed of in soil by microorganisms, similar to the way a backyard compost pile works. Choi says that a potential drawback to that approach is that the battery’s biodegradability depends on favorable landfill conditions.

Choi is working on conditions to improve the survival and performance of the freeze-dried bacteria, enabling a longer shelf life. He also has applied for a patent for the battery and is seeking industry partners for commercialization.