Scaling‐Up Microbial Fuel Cells: Configuration and Potential Drop Phenomenon at Series Connection of Unit Cells in Shared Anolyte

Abstract

To scale-up microbial fuel cells (MFCs), installing multiple unit cells in a common reactor has been proposed; however, there has been a serious potential drop when connecting unit cells in series. To determine the source of the loss, a basic stack-MFC (BS-MFC) has been devised, and the results show that the phenomenon is due to ions on the anode electrode traveling through the electrolyte to be reduced at the cathode connected in series. As calculated by means of the percentage potential drop, the degree of potential drop decreased with an increase in the unit-cell distance. When the distance was increased from 1 to 8 cm, the percentage potential drop in BS-MFC1 decreased from 46.76 ± 0.90 to 45.08 ± 0.70 % and in BS-MFC2 from 46.41 ± 0.95 to 43.82 ± 2.23 %. As the p-value of the t-test was lower than 0.05, the difference was considered significant; however, if the unit cells are installed far enough from each other to avoid the potential drop phenomenon, the system will be less dense, consequently reducing the ratio of electrode area per volume of anode compartment and decreasing the power density of the system. Finally, this study suggests design criteria for scaling-up MFC systems: Multiple-electrode-installed MFCs are modularized, and the unit cells are connected in series across the module (connecting each unit cell does not share the anolyte).

Bioelectronic platforms for optimal bio-anode of bio-electrochemical systems: From nano- to macro scopes

“…However even if a biofilm producing a high current is well formed and operated, in terms of practical application, a stack system in MFCs is required for scaling-up in order to increase the voltage output . Recently, a modulating stack system having series/parallel connections was designed in an attempt to increase the reactor volume and enhance electricity production Chang et al, 2011;Kim et al, 2012) (Fig. 2).…”

“…2). Kim et al (2012) was the first to suggest the modulation system and connect multiple electrodes, and a multiple-electrode MFC was designed as unit cell for this concept . In the same concept, to reduce the cost and to prevent biofouling, a stackable membraneless MFC using a bipolar plate was proposed .…”

Microbial fuel cells for energy production from wastewaters: the way toward practical application

“…However, MFCs may experience cell voltage reversal and ionic short circuits, making the series stack efficiency as low as 38%-41% (Ieropoulos et al, 2008;Wang and Han, 2009). Voltage reversal results from unequal electrode potentials between the unit cells, probably due to insufficient distribution of the substrate (Kim et al, 2012). Voltage reversal can be prevented by using air cathodes of high parallelism in performance, maintaining similar catalytic activity of anode biofilms, and increasing the homogeneity of substrate distribution in different unit cells.…”

Optimizing the electrode surface area of sediment microbial fuel cells

“…5): in cathode-limiting stacks, the electron and proton generations on anodes were more rapid than the consumption by cathode due to the insufficient cathode surface area, resulting excess electrons and protons that contribute to parasitic cells. 20,21 In anode-limiting stacks, the electron and proton generation of the anode was slower than the consumption by cathode, and thus less electron and proton can be used in forming parasitic cells. As a result, the cathode-limiting stacks can generate more power than the anode-limiting stacks with the same electrode surface area under separated environments because of higher reaction rate on cathode than anode.…”

“…Enlarging the distance between SMFC units has been suggested to decrease the ion-conduction. 20,21 However, the internal resistance and wire length of a SMFC stack may also increase with the distance.…”