Boosting Microbial Fuel Cell Performance by Combining with an External Supercapacitor: An Electrochemical Study

Microbial fuel cells (MFCs), despite representing a promising technology, suffer from low power generation that hinders, in most of the cases, their application as power sources. In fact, MFCs are usually coupled with supercapacitors or batteries and these storage units accumulate the energy harvested by MFCs and deliver it on demand. In this work, the electrodes of a MFC are used as electrodes of an internal supercapacitor and discharges and self-recharges are performed and investigated. Discharges between 1.5 mA and 4 mA were presented producing a maximum power of 1.59 mW. Discharges between 1 mA and 100 mA and recharges are systematically studied for three commercial supercapacitors (SCs) with different capacitances of 1 F, 3 F, and 6 F. The MFC was also connected in parallel with external SCs and discharged galvanostatically. The SC was selfrecharged by the MFC without any additional external power sources. At lower current pulses, the MFC contributed to the overall capacitance, probably owing to its faradaic component. At higher current pulses, the use of SCs enables the energy to be harvested by MFCs at power levels that could not be achieved with the MFC alone. This study demonstrates that, through the proper connection and operation mode of the MFC and SC, it is possible to improve and maximize the performance of every single unit. Understanding the MFC SC combination is important for identifying the right practical application for which the combination is suitable.