Lack of anodic capacitance causes power overshoot in microbial fuel cells

Power overshoot commonly makes the performance evaluation of microbial fuel cells (MFCs) inaccurate. Here, three types of carbon with different capacitance (ultracapacitor activated carbon (UAC), plain activated carbon (PAC) and carbon black (CB)) rolled on stainless steel mesh (SSM) as anodes to investigate the relationship between overshoot and anodic capacitance. It was not observed in all cycles of UAC-MFCs (from Cycle 2 to 4) due to the largest abiotic capacitance (Cmabiotic) of 2.1 F/cm2, while this phenomenon was eliminated in PAC-MFCs (Cmabiotic = 1.6 F/cm2) from Cycle 3 and in CB-MFCs (Cmabiotic = 0.5 F/cm2) from Cycle 4, indicated that the Cmabiotic of the anode stored charges and functioned as electron shuttle to overcome the power overshoot. With bacterial colonization, the transient charge storage in biofilm resulted in a 0.1–0.4 F/cm2 increase in total capacitance for anodes, which was the possible reason for the elimination of power overshoot in PAC/CB-MFCs after multi cycle acclimation.