Photosynthetic Microbial Fuel Cells: Sunlight to Bioelectricity
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Microbial fuel cells (MFCs) harvest electricity from microorganisms capable of catalyzing the conversion of chemical energy in organic compounds into electrical power. As any other fuel cells, MFCs consist of an anode and a cathode chamber connected together by an external circuit. The flow of electrons from the anode to the cathode generates a current. A major limitation for the use of MFCs is their cost per unit of electricity as they often require expensive catalysts, ion-exchange membranes and air-pumps. This presentation describes a photosynthetic biocathode in a sediment-type microbial fuel cell (pMFC) constructed without a proton exchange membrane and exposed to sunlight. The carbon and stainless steel cathode did not contain any catalyst, but was covered in a biofilm composed of a complex community including microalgae and cyanobacteria. The impacts of various parameters, such as temperature and dissolved oxygen, on the performance of sediment-type pMFCs were monitored. We found that higher temperatures lowered the anode potential by boosting the metabolism of the anodic biofilm. The biological production of oxygen in close proximity to the illuminated cathode significantly increased its performance as compared to that achievable with mechanical aeration. However, the photosynthetic biofilms grown in this study did not appear to catalyse oxygen reduction reactions, since a clean electrode, without biofilm, performed equally well. Instead, the reduction of oxygen at the cathode during daytime is likely to follow the peroxide pathway.