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

Abstract

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 self‐recharged 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.

Scaling up self-stratifying supercapacitive microbial fuel cell

“…Generally, the kinetic related to electrostatic processes is much faster compared to the one delivered by faradaic processes. Therefore, it can be speculated that: i) high current pulses (short t pulse ) will be associated to electrostatic processes; ii) low current pulses (long t pulse ) will be associated to faradaic processes [ 39 ].…”

“…These trends well fit with the explanation described above. It is normally extremely difficult to identify and quantify the two different contributions [ 39 , 43 ].…”

“…The capacitance is a parameter of interest in electrical double layer (DL) capacitor where the electrostatic contribution is present. It was shown that in supercapacitive MFCs, especially at low current pulse, two contributions were considered, the first electrostatic due to the double layer and the second one due to the red ox reactions occurring on the MFC electrodes [ 39 ]. Therefore, especially at low current pulses, it is more correct to utilise the term “apparent” capacitance since it is practically impossible to discriminate the two contributions.…”

“…Recently, capacitive behaviours regarding anode, cathode and overall MFC system were investigated [ [31] , [32] , [33] , [34] , [35] , [36] , [37] , [38] , [39] , [40] , [41] ]. The capacitive features of the anode were deeply investigated by increasing substantially the anode surface area [ [31] , [32] , [33] , [34] , [35] , 42 ].…”

“…The capacitive features of the anode were deeply investigated by increasing substantially the anode surface area [ [31] , [32] , [33] , [34] , [35] , 42 ]. MFCs were also operated in supercapacitive mode and discharged galvanostatically [ [36] , [37] , [38] , [39] , [40] , [41] , 43 , 44 ]. In fact, the anode and the cathode of the MFC, charged negatively and positively by the different established environments (anaerobic and aerobic/anoxic) were considered like electrodes of an internal supercapacitor, whereby an electrochemical double layer (EDL) is formed on the electrodes surface.…”