Biological capacitance studies of anodes in microbial fuel cells using electrochemical impedance spectroscopy

It is known that cell potential increases while anode resistance decreases during the start-up of microbial fuel cells (MFCs). Biological capacitance, defined as the apparent capacitance attributed to biological activity including biofilm production, plays a role in this phenomenon. In this research, electrochemical impedance spectroscopy was employed to study anode capacitance and resistance during the start-up period of MFCs so that the role of biological capacitance was revealed in electricity generation by MFCs. It was observed that the anode capacitance ranged from 3.29 to 120 mF which increased by 16.8% to 18-20 times over 10-12 days. Notably, lowering the temperature and arresting biological activity via fixation by 4% para formaldehyde resulted in the decrease of biological capacitance by 16.9 and 62.6%, indicating a negative correlation between anode capacitance and anode resistance of MFCs. Thus, biological capacitance of anode should play an important role in power generation by MFCs. We suggest that MFCs are not only biological reactors and/or electrochemical cells, but also biological capacitors, extending the vision on mechanism exploration of electron transfer, reactor structure design and electrode materials development of MFCs.