Significance of maximum current for voltage boosting of microbial fuel cells in series

Differences in internal resistances or operational conditions that affect the current between series-connected MFC units are known to cause voltage reversal. In this work, we proved that voltage reversal does not happen when MFCs produce an identical maximum current (i.e., limiting current), even though their internal resistances may differ. Here, two MFCs having an internal resistance difference of 206 Ω produced an almost identical maximum current of 0.4 mA in non-stacked mode. When the MFCs were connected in series, there was no voltage reversal; the voltage at the maximum current of 0.37 mA ranged from 1 mV to 3 mV. This result clearly indicates that differences of internal resistances or operational conditions are not an essential prerequisite for occurrences of voltage reversal in stacked MFCs, and that the maximum current of MFCs may be a direct indicator for predicting voltage reversal occurrences prior to the series connection of MFCs. Significance of the maximum current in series-connected MFCs: voltage reversal does not occur when the maximum current is the same in MFCs although the internal resistances of individual MFCs may differ from each other; the maximum current of an inferior MFC is a direct indicator for predicting voltage reversal occurrences prior to the series connection of MFCs. [Display omitted] •Differences of internal resistances are known as the cause of voltage reversal.•Internal resistances for an identical maximum current were different in MFCs.•Voltage reversal did not happen when MFCs produced an identical maximum current.•Thus, differences of internal resistances could not be the cause of voltage reversal.•The maximum current of MFCs could be an indicator for voltage reversal.