Scientists at Ames-based Iowa State University have demonstrated that three-dimensional microbial fuel cells (or MFC) could channel liquids through themselves via capillary action, thus eliminating the need for any kind of external power. Appearing in this month’s issue of the TECHNOLOGY journal, the research opens up a range of possibilities when it comes to producing electric current using MFC systems.
At the end of five straight days of operation, the paper-based MFC generates power, thanks to biofilm formation on the anode. The system, according to the team, produces around 1.3 μW of power and nearly 52.25 μA of electricity, which amounts to a power density of about 25 W/m3. As the researchers explains, the observations confirm that 3D microbial fuel cells are capable of generating usable current efficiently, without the need for any external power. Speaking about the breakthrough, Nastaran Hashemi, a professor of mechanical engineering at the university and the paper’s senior author, said:
All power created in this device is useable 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.
The biofilm creation on the carbon fiber, the scientists believe, actually indicates that the electric current measured during the test was the result of a bio-chemical reaction. This is in turn significant, since increased biofilm thickness has been found to bring about an increase in current production. The complex reactions, according to the group, involve bacterial cells metabolizing electron-rich materials with the help of special enzymes.
During these reactions, the electrons travel freely to the anode via one of the many mechanisms of electron transport. As Hashemi points out, the exact mechanism of electron transport differs for different types of bacteria. In case of the bacterium Shewanella Oneidensis MR-1, for instance, electron transfer takes place through direct contact, microscopic biological wires and excreted soluble redox molecules. Of the various methods, the last one accounts for up to 70-percent of electron transport from bacterial cells to the electrode.
As a result of the study, the team has come to the conclusion that biofilm facilitates the adsorption of redox molecules at the electrode, leading to higher power-density MF cells. Up until now, lack of adequate research had scientists associating current in bacterial cells with extracellular electron transfer. The current research therefore marks the first time that electricity-producing capacities of microbial fuel cells have been demonstrated successfully. The breakthrough, the team hopes, could pave the way for new uses of MFC systems.
Source: World Scientific