Engineers Inspired by the Stars Create Improved Microbial Fuel Cell

A team of engineers has developed a disposable battery that could be applied for challenging field conditions where small devices are required.

From a few drops of dirty water, the team developed a microbial fuel cell 2.5 inches wide that runs on the bacteria within the drops.

The previous iteration was a paper-based origami fuel cell shaped liked a matchbook with four modules stacked but a new design has improved power and voltage yields with eight batteries in series. Here's the best part: the design was inspired by an origami ninja star.

Choi showing the origami microbial fuel cell. (Image courtesy of Johnathan Cohen/Binghamton University.)

“Last time, it was a proof of concept. The power density was in the nanowatt range,” said professor Seokheun “Sean” Choi, a professor of engineering who led the research at University of Binghamton in New York. "This time, we increased it to the microwatt range. We can light an LED for about 20 minutes or power other types of biosensors."

Harnessing Power from Bacteria

Current generated by the microbial fuel cell (MFC) depends directly on the amount of energy contained within the wastewater collected. The wastewater fuel source is inexpensive and the bacteria within naturally colonize and create a biofilm on the anode. Bacteria consume the waste and give off electrons and other byproducts, thus creating the current flow of electrons to the cathode.

Wastewater is a growing problem, but by using it as the source for fuel in disposable batteries, there is the potential to create environmentally friendly solutions for a variety of applications. Starting small, Choi's team focused on paper-based biosensors in order to reduce inefficient battery usage which only creates more pollution.

Schematic of an MFC. (Image courtesy of Janelle Curtis, Biodesign Institute at Arizona State University)

With the foldable origami star, there is one inlet at its center and electrical contacts at the points of each side. Wastewater drops are placed into the inlet, and then the device is spread open to allow each of the eight fuel cells to work. Each module is a sandwich of five functional layers with its own anode, proton exchange membrane and air cathode.

Applications for Paper-Based Biosensors

These paper-based biosensors can be used for pregnancy tests and HIV tests and may create more sophisticated fluorescent or electrochemical sensors, according to Choi. The sensitivity of such tests are limited, but applying MFC technology may improve test efficiency.

“Commercially available batteries are too wasteful and expensive for the field,” he said. “I'd like to develop instant, disposable, accessible bio-batteries for use in resource-limited regions.”

The challenge Choi and his team face with the new design is to reduce cost—the previously developed matchbook design only costs five cents to produce. The origami ninja star costs approximately 70 cents, due to added materials such as copper tape and carbon cloth. By producing fully paper-based devices with the same power output, the origami star has potential to become the MFC of choice in a range of biomedical applications.

For a very different MFC application, check out this article on a self-rowing robot for environmental cleanup.