A team of researchers from Iowa State University in Ames have demonstrated a proof-of-concept three dimensional paper-based microbial fuel cell (or MFC) that could take advantage of capillary action in order to guide the liquids through the MFC system and completely get rid of the need for external power. Their complete report was published in the last issue of TECHNOLOGY journal.
The paper-based MFC runs for five consecutive days and shows the production of electrical current as a result of biofilm formation on the anode. The system produces 1.3 μW of power and 52.25 μA of current yielding a power density of around 25 W/m3 for the experiment. The results show that the paper-based microbial fuel cells can create power in an environmentally friendly mode without the use of any external power sources. Nastaran Hashemi, Assistant Professor of Mechanical Engineering and the senior author of the paper, says 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 advancements of these devices and the expansion of their applications.
The biofilm formation on the carbon cloth that occurred during testing provides even further evidence that the current measured was the result of the bio-chemical reaction taking place. This is very important information because the biofilm plays a crucial role in the current production of a microbial fuel cell. When the biofilm size is increased it leads to overall higher current production. Individual bacterial cells metabolize electron-rich substances in a complex process that involves many enzyme-catalyzed reactions. The electrons are then able to travel freely to the anode through one of many modes of electron transport. Such transportation is extremely complicated and evidence suggests that it is unique to each type of bacteria.
When it comes to Shewanella Oneidensis MR-1, the most predominantly known way of shuttling electrons from the individual bacteria cells to the anode are through direct contact, excreted soluble redox molecules, and biological nanowires. Out of these it is thought that excreted soluble redox molecules serve as extracellular electron shuttles, which make up for as much as 70% of all electron transfer mechanism from individual bacteria cells to the electrode. It has been shown time and time again that direct contact between individual S. Oneidensis MR-1 and the electrode have little impact on the current generation, which supports a mediated electron transfer from mechanism. Biofilm helps with the absorption of the redox molecules to the electrodes, allowing higher power density among microbial fuel cells.
There have not been many studies that relate to the power production created from power-based microbial fuel cells running for a handful of days. Without enough time for biofilm to form, the reported current and power data would be mainly associated with extracellular transfer, which does not completely represent electrical producing capabilities of microbial fuel cells. For the first time the device was able to demonstrate the longer duration of use and ability to operate on an individual basis. This development could help to increase the number of situations where microbial fuel cells can be applied.
The team at Iowa State University is currently exploring options that will help to better control the voltage being put out and create a much more constant current. Controlled environment tests are being conducted in order to help in the regulation of the systems output and yield far more stable results. In order to achieve optimal usability and lower costs dramatically, the team will have to begin exploring a device that would not need to use Nafion and Potassium Ferricyanide during its application.