Development of Biofilm Nanowires and Electrode for Efficient Microbial Fuel Cells (MFCs)

Abstract

In the current past, energy research has intensely focussed on alternatives to conventional resources as a global priority. Sustainable resources such as biomass and biological systems have emerged as frontlines’. Microorganisms have championed the evolution of ‘microbial fuel cell’ research due to the ease of exploring metabolism, diversity, ability to utilize a multitude of organic compounds and simultaneously generate electricity. These leads have been important in spearheading scalability and technology development of MFCs and have offered extended scope of application. One of the most important engineering challenges in MFC development is the efficient electron transfer from the bacteria to the anode. To date three possible methods of transferring electrons from bacterial cells to the electrode have been identified - directly via cell surface cytochromes (e.g. Shewanella spp), via pili acting as nanowires (e.g. Geobacter spp) or via the production of soluble electron mediator compounds (e.g. Pseudomonas sp phenazine production). It is imperative that apart from engineering variables, the efficacy of the MFC is a function of electrode material and the electron transfer mechanism. Direct electron transport (DET) through bacterial nanowires has been reported to enhance the efficiency of MFCs. For this study, it was envisaged that the latter proposition could be applied through effective biofilms for DET in MFC along with an electrode material. This would enhance the voltage output and be economical. Therefore, initially bacterial cells with electrogenic and biofilm forming ability were screened from infant fecal samples and selected for MFC development. A dual chamber MFC setup was developed with varying types of electrode materials to optimize the electrode with maximum current output. The results indicated that salt bridge based MFC with graphite as electrode produced a maximum voltage of 447mV which was low in comparison to 615.45mV produced by the aluminium electrode with biofilm on its

surface, after an incubation of 96 hours at 30˚C. Scanning Electron Micrographs revealed biofilms and the formation of nanowire by the bacterial cells which helps in DET. The salt bridge based MFC with biofilm on aluminium electrode was used as a source of power for scientific calculator which could be operated at 1 V power supply. Arrays of MFCs were thereafter used to power an infrared sensor based object detector. The results of this study suggest a potential applicability of the MFC as an alternative renewable energy source for electronic devices.