Elimination of Power Overshoot at Bioanode through Assistance Current in Microbial Fuel Cells

Abstract

The power overshoot generated by electron depletion in microbial fuel cells (MFCs) was characterized in this study. Various causes of power overshoot, identified in previous studies, are discussed in terms of their plausible contributions to electron depletion. We found that power overshoot occurred if the anodic overpotential generated by electron depletion exceeded the cathodic overpotential. The introduction of assistance current from anode connections, which ameliorated the electron depletion in the MFCs, immediately eliminated the power overshoot. As a result, if the electron production at the anode exceeded electron reduction at the cathode, a power overshoot was not generated. The results revealed that introducing assistance current supplied from an additional anode to the limited anode eliminated power overshoot. The power overshoot is not generated by kinetic limitation at the cathode; it is only generated by the kinetic limitation at the anode. The mechanism underlying power overshoot should be considered in the design of MFCs to improve reliability, particularly in scaled-up plant applications. The proposed technique is more practical than previously proposed methods.

High‐performance Microbial Fuel Cell Using Metal Ion Complexes as Electron Acceptors

“…The V oc of the series connection was 3.06 V; but the average V oc (1.02 V) was lower than those of other connections. The parallel‐connected battery will be similar to 3A–3C connected in parallel in the reference . Difference between the present study and the study in the reference is that the unit cells are completely separated in the present study, while anolyte was common in the reference .…”

“…These results demonstrate that the battery performance was improved by driving out the electrons generated in the bio‐anode with an increase in the cathode reduction reaction rate . Therefore, the high‐performance MFC battery can be optimized by using a reversible electron acceptor of high reduction potential at a morphologically porous carbon cathode, while avoiding electron depletion at bio‐anode causing concentration polarization quenching or power overshoot …”

“…Electron acceptors of high reversible reduction potential could produce high electrical capacity, power, and energy with carbon brush cathode, when the biofilm‐coated carbon brush anode is applied. In this study, under the similar parallel‐connected condition (3A–3C), 5000 ppm [Fe(III)(4,4′‐dimethyl‐2,2′‐bipyridyl) 3 ]‐MFC produces optimum current approximately 1.2 times (4.9–6.0 A/m 2 ) and optimum electrical power approximately 3.6 times (1.13–4.0 W/m 2 ) higher than those of a single‐chambered O 2 ‐MFC, when calculated based on the cathode area . O 2 ‐MFC contained 12.25 cm 2 nonwet‐proofed carbon cloth anode and 10% wet‐proofed carbon cloth cathode of the same area containing Pt catalyst.…”

“…The parallel‐connected battery will be similar to 3A–3C connected in parallel in the reference . Difference between the present study and the study in the reference is that the unit cells are completely separated in the present study, while anolyte was common in the reference . These situations do not seem to affect the results for the parallel‐connection condition.…”

“…For the parallel‐connected battery, 120 mAh and 96 mWh were obtained at the constant current of 3.0 mA at the same concentration. The parallel‐connected battery allowed a 3.4 times higher performance in the capacity and 1.4 times higher performance in the energy than the series‐connected battery because the electrons generated at the bio‐anode flowed more freely for the former than the latter . The power overshoot of the parallel‐connected battery (3A–3C) is eliminated, and the battery performance becomes improved, when depletion rate at bio‐anode is slowed down .…”