IJERD – International Journal of Environmental and Rural Development (2022) 13-1

Research articleerd

Enhancement of Carbon Fiber Electrode Performance using
Lactic Acid Bacteria and Steelmaking Slag
NARONG TOUCH*
Faculty of Regional Environment Science, Tokyo University of Agriculture, Japan
Email: nt207118@nodai.ac.jp

TADASHI HIBINO
Graduate School of Advanced Science and Engineering, Hiroshima University, Japan
Received 14 January 2022

Accepted 25 April 2022(*Corresponding Author)

Abstract Microbial fuel cell technology (MFCT) provides many benefits to rural regions,such as organic waste disposal and renewable energy recovery. However, its performance islow and must be improved for practical uses. Mixing steelmaking slag (SS) and lactic acidbacteria (LAB) with sediment can enhance the MFCT performance owing to LAB and iron
ions dissolved from SS attaching to the electrode surface. This study proposes a simple
method for attaching LAB and iron ions on carbon fiber electrode and subsequently
evaluating its performance. A carbon fiber electrode was placed in a bottle containing tap
water, SS, LAB, and bamboo powder (as nutrients for bacteria) for 7 days to allow LABand iron ions to adhere to its surface. The electrode was then used as the cathode of MFCT.
Results showed a decrease in the electrode potential and a consequent reduction in MFCT
performance owing to the attached LAB and iron ions. The performance improved after theelectrode was oxidized, suggesting that aeration is required during attachment to prevent thedecrease in electrode potential. After 1 month of electricity generation, the electrode withthe attachment produced high electrical current and exhibited low decrease in MFCT
performance owing to electricity generation. Therefore, attaching LAB and iron ions on theelectrode surface can improve the electrode performance and prevent performancedegradation owing to electricity generation.
Keywords microbial fuel cell, performance, electrode potential, attachment,
steelmaking slag, lactic acid bacteria

INTRODUCTION
Microbial fuel cell technology (MFCT) offers many benefits for rural regions, particularly indeveloping countries. For example, this method can be used to treat agricultural wastewater,household sewage, and organic waste, provide electricity to households, and recycle resources tofarmlands (Touch et al., 2020). However, the performance of MFCT remains low and must beimproved for practical uses. MFCT efficiency depends on the cathode and anode. A low electrode
performance will restrain the overall performance of MFCT. According to Yamasaki et al. (2018),
various types of potential losses occur during electron flow to an electrode. One of which isactivation loss that strongly influences electrode performance. Activation loss should be minimized
via pretreating the electrode to obtain a high MFCT performance. Furthermore, this loss increases
during electricity generation owing to the crystallization of ions present in water on the electrodesurface. Thus, a method for minimizing the performance reduction owing to electricity generationis necessary.
Adsorption of bacteria or metal ions on the electrode surface is a method for improving theelectrode performance. Wang et al. (2009) successfully enhanced electrode performance byactivating the bacteria at the electrode and consequently reducing potential losses. The boosted
electrode performance through bacterial attachment and biofilm formation has been widely studied
using the cyclic voltammetry measurement (Carmona-Martinez et al., 2011; Kang et al., 2012).
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Electrode performance can also be improved via coating a catalyst on the electrode surface.
Many types of catalyst have been used in chemical reactions, such as iron ions. Nishimura, et al.
(2018) reported that ferric ions dissolved from steelmaking slag (SS) improve sediment microbial
fuel cell (SMFC) performance. Using SS and lactic acid bacteria (LAB) in the anode of SMFC canalso enhance its performance (Touch et al., 2020). On this basis, the attachment of iron ions andLAB on the electrode surface can increase the electrode performance.
OBJECTIVE
This study proposed a simple method for attaching LAB and iron ions dissolved from SS on carbon
fiber electrode. Changes in electrode potential and electricity generation (electrode performance)
owing to the attachment were subsequently investigated via measuring the polarization (currentvoltage relation) of electrode to determine changes in potential loss and examining the current todetect alterations in MFCT performance when the electrode is used as the cathode. The effects ofthe attachment on MFCT performance reduction owing to electricity generation were also
discussed.
METHODOLOGY
Experimental Materials and Procedures
Dip-coating and electrodeposition are used to attach metal oxides on an electrode surface. For
practicality, a simple attachment process should be considered. Iron ions dissolved from SS are
adsorbed on the cathode of MFCT during long-term electricity generation (more than 6 months).
This study focuses on how to attach iron ions dissolved from SS to a carbon fiber electrode in ashort span (1 week).
Cylindrical bottles (120-mm inner diameter and 150-mm height) were filled with 500-mL tap
water. Some bottles contained 20-mm depth of SS and 20-mL lactic fermenting beverage, as shownin Fig. 1. Bamboo powder (5 g) was then added to the bottles and reduced the solution pH becauseof its fermentation. This process facilitates the dissolution of iron from SS. Furthermore, nutrientsfrom bamboo powder can activate LAB. Therefore, iron ions and LAB can attach to the electrodesurface in a short span.

Fig. 1 Experimental devices and materials
The electrode material was carbon cloth (News Company, PL200-E), preheated at 500°C for 1
h to improve its performance (Nagatsu, et al. 2014). The heated carbon cloth with a 100-mm widthand length was separated into fibers to form a brush-type electrode (photo in Fig. 1), which wasthen placed in the bottle for 7 days during bamboo powder fermentation.

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Operations and Measurements
Experiments were conducted following the procedures in Fig. 2. The electrodes were placed in thesolution for 7 days and then extracted from the bottle to measure their polarization using the circuitin Fig. 2a. In particular, the anode potential was fixed at −0.64 V to display a clear variation of thecathode (the electrode taken from the bottle) performance. An external resistance with 2.2 Ω–10kΩ was loaded between the anode and cathode. Cell voltage was recorded 1 min after loading eachexternal resistance and used to calculate the current according to the Ohm’s law: I = U/Rex, whereU [V] is the voltage, I [A] is the current, and Rex [Ω] is the external resistance. Power P wascalculated according to P = IU. Current and power densities were obtained by dividing these values
by the surface area of the electrode, i.e., 0.01 m2.
After polarization measurements, the electrodes were placed in the bottle filled with tap water
near the water surface for 7 days to examine the effects of oxidation on the electrode performance.
The polarization of each electrode was remeasured after oxidation. The electrode was used as thecathode of SMFC (Fig. 2b) for 1-month electricity generation to examine its long-termperformance. For electrical current generation, an external resistance of 2.2 Ω was loaded between
the anode and cathode. Although different SMFCs were used for each case, the initial anode
potential of each SMFC was the same order of magnitude.
CathodeExternal resistance

20 mL of lactic
fermenting beverage
5 g of bamboo powder

Tap water (500 mL)

Tap water (1 L)
RAnodeV
Potentiostat
For a fixed
potential of -0.64 V(a) Polarization measurements
120 mmElectrode oxidation (7 days)

Tap water
2.2 ΩVPolarization measurements

Paddy soil

50 mm

➢ Polarization measurements

100 mm7 days<Anode >Steelmaking slag
(100*100) mm2 –brush type(b) Current generation (30 days)

Fig. 2 Operations and measurement methods
After electricity generation, polarization and exchange current density were measured to
examine the effects of electricity generation on the electrode performance. Exchange current
density is an index for evaluating activation losses at the electrode surface, that is, a high exchange
current indicates a small potential loss, i.e., a high electrode performance. Exchange current density
was determined using the method noted in the study by Nagatsu et al. (2014).
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Effects of LAB and Iron Ion Attachment on the Electrode Performance

0.4

Electrode potential (V vs. Ag/AgCl)

Electrode potential (V vs. Ag/AgCl)

After fermentation and when each electrode was place in tap water, the electrode potential wasmeasured to examine the effects of LAB and iron ion attachment on the electrode performance.
Comparison of electrode potential is shown in Fig. 3. The electrode potential largely decreased
from 0.36 V (Case 1) to 0.01 V (Case 2) owing to LAB adsorption, to 0.06 V (Case 3) owing toiron ion adsorption, and to -0.11 V (Case 4) owing to LAB and iron ions adsorption (Fig. 3a). Afterthe electrode was oxidized for 7 days (Fig. 3b), the electrode potential (Cases 2-4) largely increased(from 0.20 V to 0.25V).
These results indicate that the proposed method can attach LAB and iron ions dissolved fromSS to the carbon fiber electrode. However, the attachment decreases the electrode potential.
Consequently, the MFCT performance is reduced when the electrode is used immediately after theattachment. Given that electrode oxidation increases its potential, oxidizing the electrode with theattachment should be conducted before its usage in MFCT. Aeration should be performed duringattachment to prevent the decrease in the electrode potential.

0.3
0.2
0.1
0-0.1

0.4

0.35
0.3
0.25

0.2
0.15

0.1
0.05

-0.2

0
Case 1Case 2

Case 3

Case 1Case 4(a) after attachment

Case 2

Case 3

Case 4(b) after electrode oxidationFig. 3 Comparison of electrode potential at different conditions
Changes in Electrode Performance Owing to the Attachment of LAB and Iron Ions

50454035302520151050

Exchange current density (mA/m2)

Current density (mA/m2)

Fig. 4 compares of the electrode performance of each condition. The electrode without attachment(Case 1) produced only approximately 3 mA/m2 of current density. Meanwhile, the electrodeattached to either LAB (Case 2) or iron ions (Case 3) generated 30–35 mA/m2, a 10-fold increases(Fig. 4a). These results indicate the improved electrode performance can be attributed to theadsorption of LAB or iron ions on the electrode surface. A further increase in current density wasalso observed when LAB and iron ions were attached to the electrode (Fig. 4a, Case 4). Therefore,irons ions aid LAB to transfer electrons to electrode.

Case 1Case 2
Case 3
Case 405101520259080706050403020

10030

Case 1

Operating time (day)(a) temporal change of current density

100Case 2

Case 3

Case 4(b) exchange current density after current generationFig. 4 Comparison of the electrode performance of each conditionⒸ ISERD

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The exchange current density of each case was compared in Fig. 4b. As shown in Fig. 4b, theexchange current density increased after the attachment of either LAB or iron ions on the electrodesurface. This finding indicates that the potential loss at the electrode surface is reduced owing to
the attachment, i.e., electrons are easily transferred to electrode via LAB or iron ions. In addition,
the exchange current density of the electrode with iron ions attached (Case 3) was 80 mA/m 2 which
was two-fold higher than that of the electrode with attached LAB (Case 2, 40 mA/m2). Iron ion
attachment provides a better performance than LAB attachment. However, the combination of LAB
and iron ions exhibits a higher performance than the use of each component alone.
Reducing the Performance Decrease Owing to Electricity Generation by LAB and Iron ions

200180160140120
100
8060
40200

Case 1Case 2

Case 3

Case 4

Power density (mW/m2)

Power density (mW/m2)

Figures 5a and 5b depict the comparison of performance (current and power density relationship)for electrodes with and without electricity generation. Power density and current density decreased
owing to electricity generation. In the experiments, crystallized compounds were observed on theelectrode surface and can contribute to the decrease in performance.

0100200

300

400

500

200
180160140120
100
8060
40200

Case 10600

100

Case 2200

Case 3300

Case 4400

500

600

Current density (mA/m2)

Current density (mA/m2)(a) without electricity generation(b) with electricity generation

Fig. 5 Comparison of performance for electrodes with and without electricity generation
An 80-mW/m2 reduction in power density was observed for the electrode without attachment(Case 1) and 70-mW/m2 reduction for the electrode with iron ion attachment (Case 3). Only 12mW/m2 reduction in power density was observed when LAB attached to the electrode surface withand without iron ions (Cases 2 and 4). Therefore, LAB attachment on electrode surface effectively
improves the reduced performance owing to electricity generation. Crystallization cannot occur onthe electrode surface with LAB.
CONCLUSIONS
Laboratory experiments were conducted to verify the efficiency of the proposed simple method forattaching LAB and iron ions on a carbon fiber-electrode and to examine the effects of attachment
on the electrode performance. Approximately 300-mV reduction in electrode potential wasobserved owing to the attachment. Nevertheless, the electrode potential recovered almost to theinitial state after oxidizing the electrode by placing it in tap water near the water surface for 7 days.
Thus, aeration should be conducted during attachment to prevent the decrease in the electrodepotential. A 10-fold increase in current density was observed for the electrode attached with either
LAB or iron ions. A high increase in current density was obtained when LAB and iron ions wereattached to the electrode. On the basis of the increase in exchange current density owing to theattachment, the potential loss at the electrode surface is reduced owing to the attachment, i.e.,electrons are easily transferred to electrode via LAB or iron ions. Finally, the performance decrease
owing to electricity generation was largely (88%) reduced for the electrode attached to LAB.
Therefore, the attachment of LAB on the electrode surface can restrain the formation of crystallizedcompounds.
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ACKNOWLEDGMENTS
The authors gratefully acknowledge the partial funding from JSPS: Grant-in-Aid for Scientific
Research (B) (Grant Number: JP-21H01437). The authors would also like to thank the students of
the Rural Environmental Engineering Laboratory, Tokyo University of Agriculture, for their efforts
in collecting data.
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