The prototype paper-based MFC runs for five days and produces 1.3 μW of power and 52.25 μA of current yielding a power density of approximately 25 W/m3. These results show that the paper-based microbial fuel cells can create power in an environmentally friendly mode without the use of any outside power.
“All power created in this device is usable because no electricity is needed to run the fluids through the device. This is crucial in the advancement of these devices and the expansion of their applications,” says Dr Nastaran Hashemi, Assistant Professor of Mechanical Engineering and the senior author of the paper.
The device allows flow of the streams of Shewanella Oneidensis MR-1 bacteria (shown in yellow above) and the Potassium Ferricyanide (white) into the chambers. A proton exchange membrane is placed between the two chambers to separate the two liquids as well as allow the positively charged ions released in the biocatalytic breakdown of the anolyte to flow from the anode to the cathode.
The biofilm formation on the carbon cloth during the test provides further evidence that the current measured was the result of the bio-chemical reaction taking place. The biofilm plays a vital role in current production of a microbial fuel cell as increased biofilm size and thickness leads to increased current production. Individual bacterial cells metabolize electron-rich substances in a complex process involving many enzyme-catalyzed reactions. The electrons are then free to travel to the anode through one of many modes of electron transport.
The protype shows that the direct contact between individual bacteria and the electrode has little impact on the current generation, supporting a mediated electron transfer mechanism. The biofilm helps with the adsorption of molecules at the electrode, which makes it important to have in high power density microbial fuel cells.
This device for the first time demonstrates the longer duration of use and ability to operate individually, a development that could help increase the number of situations where microbial fuel cells can be applied. The Iowa State University team is currently exploring options to better control the voltage output and create constant current well as lower cost chemicals.