Alp Yetisgin, PhD

Every cell, either bacteria, yeast, fungi or even our body cells, produce energy by broken down sugars and fat to continue living. However, did even you thought that this energy could be utilized to powering a cell phone or a laptop?

Microbial fuel cells (MFCs) are one of the recent trends in bioenergy researches. MFCs are devices which use living microbes as catalysts for the conversion of organic fuels into electricity.

Basically, MFC technology uses electrogenic bacterial strains which can transfer electrons produced via their metabolism across the cell membrane to an external anode. Then, these extracted electrons further delivered through an external load to the cathode to reduce an oxidant, thus producing a current. To maintain electrochemical neutrality of the system, protons in the anolyte will diffuse through the proton exchange membranes (PEM) to the cathode chamber concurrently with electron transfer.

As you all can see above, the MFC reactor consists of an anode and a cathode compartment that are separated by a proton exchange membrane (PEM). Even most of the MFCs are the two-chambered, researches also made for single chambered air-cathode MFCs which utilize oxygen as redox agent. Generally, single-chambered MFCs show performance enhancement from the two-chambered MFCs with similar environmental and operating conditions. But air-cathode is not compatible with microfabrication and requires expensive catalysts and Nafion solutions.

I gave some info about the MFC system but, another crucial thing in this technology is the bacterias that produce and transfer the electrons to the system. So, mostly searched organisms for heterotropic MFCs are Geobacter species and Shewanella species, Pseudomonas species and also fsggsdSaccharomyces cerevisiae. All these microbes transfer their electrons by the mechanism called “Extracellular Electron Transfer (EET)”. As you can see the figure above shows three different EET mechanism happen in a variety of microbes.

1. Direct electron transfer occurs between electron carriers in the microorganism and the external electrode.
2. A soluble electron shuttle is a compound that uses diffusive transportation to carry electrons from the bacteria to the electrode, with which it can react and discharge its electrons.
3. A solid, extracellular component in the biofilm matrix, that is conductive for electron transfer between the microbes and the electrode, is supported by recent discoveries about the possible role of cellular pili as nanowires, which are being characterized for their conductive capabilities.

As for the electrical power produced from these fuel cells; there is not enough answer for that, because the researches are done in different scales of anode and cathode chambers. However, if I need to give an answer to that, I can give this example: The mL-scale MFC using graphite felt (GF) as electrode produced power over 0.5 mW, which is sufficient for powering the autonomous sensor networks/nodes. Well, it is not enough for charging your phone but if you combine dozen of these MFCs like series of batteries, you might achieve the power level you need. Therefore, I can clearly say this; the microbial fuel cell technology has lots of potentials and future applications waiting for researchers to discover them.

For further reading:
Sivasankar, V., Mylsamy, P., & Omine, K. (2018). Microbial Fuel Cell Technology for Bioelectricity.
Choi, S. (2015). Microscale microbial fuel cells: advances and challenges. Biosensors and Bioelectronics, 69, 8-25.
Gadhamshetty, V., & Koratkar, N. (2012). Nano-engineered biocatalyst-electrode structures for next generation microbial fuel cells. Nano Energy, 1(1), 3-5.
Chiao, M. (2008). A microfabricated PDMS microbial fuel cell. Journal of Microelectromechanical systems, 17(6), 1329-1341.
Qian, F., & Morse, D. E. (2011). Miniaturizing microbial fuel cells. Trends in biotechnology, 29(2), 62-69.