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Article

Study of the Use of Gas Diffusion Anode with Various Cathodes (Cu-Ag, Ni-Co, and Cu-B Alloys) in a Microbial Fuel Cell

by
Paweł P. Włodarczyk
* and
Barbara Włodarczyk
*
Institute of Environmental Engineering and Biotechnology, University of Opole, ul. Kominka 6a, 45-032 Opole, Poland
*
Authors to whom correspondence should be addressed.
Energies 2024, 17(7), 1636; https://doi.org/10.3390/en17071636
Submission received: 21 February 2024 / Revised: 21 March 2024 / Accepted: 22 March 2024 / Published: 29 March 2024
(This article belongs to the Section A4: Bio-Energy)
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Abstract

:
Advancing microbial fuel cell (MFC) technologies appears to be a crucial direction in bolstering wastewater treatment efforts. It ensures both energy recovery (bioelectricity production) and wastewater pre-treatment. One of the problems in the widespread use of MFCs is the generation of a small amount of electricity. Hence, a pivotal concern revolves around enhancing the efficiency of this process. One avenue of investigation in this realm involves the selection of electrode materials. In this research, a carbon-based gas diffusion electrode (GDE) was used as the anode of MFC. Whereas for the cathode, a copper mesh with various catalysts (Cu-B, Ni-Co, and Cu-Ag) was used. This research was conducted in glass MFCs with the sintered glass acting as a chamber separator. This research was conducted for various electrode systems (GDE/Cu-Ag, GDE/Ni-Co, and GDE/Cu-B). This study analyzed both the electrical parameters and chemical oxygen demand (COD) reduction time. In each case (for each electrode system), bioelectricity production was achieved. This work shows that when GDE is used as the anode and Cu-B, Ni-Co and Cu-Ag alloys as the cathode, the most efficient system is the GDE/Cu-Ag system. It ensures the fastest start-up, the highest power density, and the shortest COD reduction time.

1. Introduction

The European Union aims to achieve carbon neutrality by 2050 while simultaneously fulfilling energy requirements [1,2,3,4,5]. Nevertheless, attaining this objective will necessitate lifestyle modifications. It will be necessary to get used to increasing the use of energy at certain times of the day, reducing water consumption, and increasing costs related to, e.g., replacing heating devices or the need to invest in installations using renewable energy sources. Unfortunately, such a change can be difficult for large groups of society to accept. Reluctance and concerns related to this will arise from the need to increase energy prices and limits on its consumption [1,2,6]. This scenario arises from the ongoing rise in living standards across various regions worldwide, correlating with a growing energy demand. The result of increasing energy production has a significant impact on the environment. Therefore, if we want to maintain a healthy natural environment, a lifestyle change will be necessary [6]. The second element that enables a reduction in the negative impact of energy production is the use of devices using renewable energy sources. For this reason, eco-friendly technologies are being rapidly developed and introduced, e.g., PV cells, wind turbines, heat pumps, etc. [7,8,9]. Moreover, hydrogen usage is gaining momentum, poised to be a cornerstone of the future energy sector [10,11,12,13,14,15]. Hydrogen will be used both in fuel cells, combustion engines and in gas turbines [16,17,18,19,20,21]. One such device includes microbial fuel cells (MFCs) [6]. MFCs ensure both bioelectricity production and wastewater pre-treatment [6,22]. One of the parameters that can be reduced in MFCs is, for example, the chemical oxygen demand (COD). This parameter may also be an indicator of the efficiency of MFCs’ operation [6,22,23]. In times of constant increases in the generation of larger amounts of wastewater, their management and use for energy production is becoming a necessity. Therefore, research of MFCs technologies seems to be the right direction to support wastewater treatment and bioelectricity generation [22,23,24]. The first report on the production of electrons by microorganisms was in 1911 [25]. However, research on the application of MFCs began to be conducted only in the 1960s [26], this is mainly because of the belief that the addition of expensive mediators was necessary to produce bioelectricity using MFCs. However, research published in 1999 showed that a naturally existing consortium of bacteria can produce electricity without the mediators [27]. Since then, there has been intense interest in the subject of MFC technology [28,29,30]. One of the problems in the widespread use of MFCs is the generation of a small amount of electricity. Therefore, an important issue is to increase the efficiency of this process. MFCs are a bio-electro-chemical system where electricity is generated by microorganisms [31]. MFCs most often consist of two chambers (anode and cathode), although there are also other designs, such as single-chamber systems. The anode chamber contains a biofilm with electron-producing microorganisms. This chamber is supplied with a medium for the microorganisms, which can include pure substances like acetate, glucose, cysteine, and ethanol, as well as mixed and heterogeneous substances like wastewater. The cathode chamber contains an oxygenated cathode. This chamber can be filled with either wastewater or, for example, an acid or alkaline solution. The chambers are typically separated by a proton exchange membrane (PEM) or sintered glass [6,22,32]. Figure 1 illustrates the principle of MFC operation.
An example of a summary reaction is one with the use of pure glucose in a MFC. As a result of this reaction, electricity along with H2O and CO2 are obtained [6]. For a glucose reaction, we obtain [33,34]
ANODE   C 6 H 12 O 6 + 6 H 2 O → 6 C O 2 + 24 H + + 24 e −
CATHODE   24 H + + 24 e − + 6 O 2 → 12 H 2 O
S u m m a r y   r e a c t i o n : C 6 H 12 O 6 + 6 O 2 → 6 C O 2 + 6 H 2 O + e l e c t r i c i t y
The oxidation of organic material (e.g., wastewater) occurs at the anode, where bacteria oxidize organic matter to produce electrons (e−) and H+ ions. This process also generates an additional volume of CO2. Meanwhile, at the cathode, H2O is produced through the reaction of electrons (e−) with H+ ions and O2 [6,35]. This is a result of cathode aeration in the cathode chamber.
In the MFC, the microorganisms act as an anode catalyst [6,24]. Therefore, the process of direct electricity production is a slow process. One of the directions of research in this area is the selection of electrode materials, on which microorganisms willingly grow, and that ensure good electron flow [6,32,36]. The microorganisms that take over the function of a catalyst at the anode (and are fed biodegradable raw materials, e.g., wastewater) are bacteria, e.g., Alfaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria, Clostridia, Bacteroidetes, Flavobacteria, Sphingobacteria, Deferribacteres, Spirochaetes, Planctomycetes, Nitrospirales or fungal cells, e.g., Saccharomyces or Pichia [6,37,38,39,40,41]. However, bacteria are most often used in MFCs [42]. Additionally, the anode biofilm hosts numerous unidentified microorganisms. Nonetheless, the synergy of diverse microorganisms thriving together proves most effective as a catalyst in the anode biofilm [6,32,42]. During the microorganism’s development in the biofilm form, one can notice at various stages, both the development of non-electroactive bacteria (non-EAB) and electroactive bacteria (EAB). In the case of MFCs, it is important to ensure the development of EAB bacteria. On the anode during the biofilm development on MFCs’ electrodes, two main stages of development of the bacterial community occur. During the first stage, all types of bacteria first settle on the electrode, and all types of bacteria begin to grow. Next, the second stage starts when the biofilm development begins. This stage involves a constant increase in the share of EAB in the biofilm. The stage of completion of biofilm formation for MFCs ends when the number of EAB significantly outweighs the number of non-EAB in the biofilm [43,44]. Since then, it can be considered that the electrode (with biofilm—EAB) is ready for use in the MFC.
One crucial role of the anode is to facilitate conducive conditions for biofilm growth while ensuring proper conductivity [31,32,36]. Therefore, various new electrode materials are constantly being sought. Various materials are used for anodes in MFCs, with carbon-based electrodes such as cloth, paper, fiber, etc., being the most common [6,22,36]. In order to promote the extensive adoption of MFCs, there seems to be a necessity to investigate novel electrode materials capable of improving the efficiency of these systems. Attempts have also been made to modify the size and shape of the anode. Notably, that increase the porosity and surface area available to electrochemically active organisms enable efficient growth [45]. Therefore, research is being carried out on the use of, for example, activated carbon as a material for electrodes (anodes) [46]. The augmentation of anode surfaces, such as facilitating the growth of bacteria in the form of a biofilm, has been observed to significantly boost energy production in MFCs [47]. Previous research indicates that this approach can lead to a substantial improvement in overall cell efficiency [48].
Therefore, research on new biocompatible electrodes (mainly carbon-based) that ensure both a large surface area and adequate conductivity seems to be important. The form of the electrode is also an important parameter, ensuring, e.g., its transfer (together with the biofilm to another MFC).
This work analyzes the impact of using a gas diffusion electrode (GDE), primarily designed for hydrogen fuel cells, on MFC operation. This work is a continuation of research on new uses of new electrodes in MFCs [49]. In this work, the feasibility of using the GDE as an anode was analyzed, in cooperation with the previously analyzed cathodes.

2. Materials and Methods

Because the working electrode (anode) in the MFC needs to ensure high biocompatibility for the appropriate development of microorganisms, a carbon-based electrode was chosen for this research. One material that provides a large surface for the development of microorganisms is activated carbon. However, activated carbon grains do not provide adequate electrical conductivity. Furthermore, when using such grains, there can be difficulties in transferring the microorganisms (biofilm) to another MFC. Therefore, it was decided to use an electrode containing carbon grains in the form of an electrode on a steel mesh. Such an electrode can also be cut to any required size. Consequently, for this research, a gas diffusion electrode (GDE), primarily designed for use in fuel cells (FC), was chosen. The anode used in this research was manufactured by Gaskatel (Gaskatel GmbH, Kassel, Germany) (Figure 2A; Figure 3, 4). The electrode composition was determined using energy dispersive X-ray spectroscopy (EDS). This method provides semi-quantitative elemental composition information by analyzing the X-rays released from atoms when irradiated with electrons. The electrode composition was determined using a Phenom XL scanning electron microscope (Phenom-World B.V., Eindhoven, Netherlands). Whereas, for the cathode (of MFC), copper mesh (Figure 2B) with Cu-B, Ni-Co and Cu-Ag catalyst was used (Figure 3, 7). The analysis of catalysts (Ni-Co, Cu-B, and Cu-Ag alloys) was performed in previous works [50,51,52,53,54].
Figure 2 shows a view of the GDE (anode) and the copper mesh to the catalysts deposition (cathode).
The cathode catalysts were acquired through electrochemical deposition onto copper mesh. The Cu-B alloy was formed through deposition using a mixture primarily composed of NaBH4 and CuSO4 [50,51]. The Ni-Co alloy was formed through deposition using a mixture primarily composed of NiSO4 and CoSO4 [52,53]. The Cu-Ag alloy was formed through deposition using a mixture primarily composed of CuSO4 and AgNO3 [54,55,56,57]. The alloys were acquired within a temperature range of 355–365 K and under a current density of 1–3 A·dm−2. The mixture composition was determined through experimental selection. The electrodeposition was conducted using a controlled power supply (PowerLab 305D-II, China). Table 1 displays the composition of the mixture utilized for catalysts deposition.
For construction of the MFC, a glass reactor (made of borosilicate glass) was used. A chamber separator made of sintered glass was used (number 8 in Figure 3). The cathode chamber (Figure 3, 5) was placed partially above the anode chamber. During MFC operation, in the cathode chamber, the cathode was constantly aerated (~2 L·h−1) (Figure 3, 1). To ensure anaerobic conditions for the biofilm on the anode and prevent the gradual oxygenation of the wastewater, the anode chamber was tightly closed with a stopper (printed in 3D technology, from a rubber-like material characterized by high flexibility and tensile strength) (Figure 3, 6). A M200 3D printer (Zortrax S.A, Olsztyn, Poland) was used to obtain the 3D printout. Additionally, carbon dioxide (produced by microorganisms) was removed through a thin pipe (Figure 3, 2) and directed to a water scrubber (preventing oxygen from the air from entering the anode chamber). Figure 3 illustrates the schematic and perspective view of the MFC used in this study.
The use of a separator in the form of sintered glass does not fully protect against oxygenation of the anode chamber, but it reduces the costs of MFC construction. By using sintered glass, the high-cost proton exchange membrane (PEM) could be eliminated.
The microorganisms used for testing were sourced from a previously operational MFC, where they had originally been collected from activated sludge obtained from a municipal wastewater treatment plant (WWTP). The use of microorganisms from a previously operational MFC enables faster biofilm development on the anode. Ensuring the cultivation of electricity-producing microorganisms involves allowing electricity to flow through the biofilm. Otherwise, both electricity-producing and non-electricity-producing microorganisms develop evenly [41,58,59,60].
During the operation of the MFC, both the electrical parameters and the reduction of COD were monitored and recorded [61]. The electrodes of the MFC remained continuously connected to a 100 Ω external load (Figure 3, R). The set of electrodes was tested in the GDE/Cu-Ag, GDE/Ni-Co and GDE/Cu-B systems. The electrical parameters of the MFC were analyzed using an 8840A multimeter (Fluke Corporation, Everett, WA, USA) and a PGSTAT302N potentiostat (Metrohm-Autolab BV, Utrecht, The Netherlands).
In this study, municipal wastewater (MWW) sourced from a wastewater treatment plant (WWTP) was utilized. The initial value of COD was 999–1022 mg·L−1. The COD concentration was assessed immediately after inundating the MFC with wastewater and after one cycle of MFC operation. The HI 83224 photometer and the HI-801 Iris spectrophotometer (both instruments made by HANNA Instruments, Woonsocket, RI, USA) were utilized for measuring COD reduction.
The temperature during all measurements was maintained at 25 °C. To carry out measurements at a set temperature during the tests, the MFC was immersed in thermostat water. To maintain the temperature, a Medingen E5s-B12 thermostat (GK Sondermaschinenbau GmbH, Labortechnik Medingen, Germany) was utilized. For the temperature measurements, a UT804 multimeter (UNI-Technology, Hongkong) was used.

3. Results and Discussion

In the first step, the analysis of gas diffusion electrode was performed. Figure 4 provides a magnified depiction of the gas diffusion electrode surface along with its chemical composition.
The data analysis showed a high carbon content of over 90% atomic concentration (over 85% weight concentration). Therefore, this electrode (GDE) has a high biocompatibility for microorganisms (which will create the biofilm). According to the data, the electrode also contains oxygen, fluorine, and sulfur. These elements may affect the functioning of the biofilm on the electrode. Generally, e.g., oxygen, fluorine or sulfur may decrease the efficiency of the anode. However, in the case of this study, it was important to check whether the currently manufactured electrode (intended for fuel cells) can be used in MFCs without additional preparation. After carrying out this series of measurements, it would be important in subsequent studies to analyze the possibility of eliminating these elements from the electrode setup in order to make measurements and compare them with the results obtained in this work.
Subsequently, the electrical parameters were measured during MFC operation. First, the cell voltage was analyzed. Figure 5 shows the cell voltage during MFC start-up for the various electrode configurations.
In general, all results indicate that the cell voltage value during the start-ups (especially during the first two start-ups) is very low. During the first start-up, the MFC generated virtually no cell voltage for a long time (100 h for GDE/Cu-Ag system; 150 h for GDE/Ni-Co system; 250 h for GDE/Cu-B system). Following three cycles, the cell voltage of the MFCs stabilized, signifying the successful initiation of the MFCs. As depicted in Figure 5, the MFC equipped with the GDE/Cu-B system exhibited the longest start-up time, lasting up to 210 h. The MFC featuring the GDE/Ni-Co system had a slightly shorter start-up time of 130 h, and the MFC utilizing the GDE/Cu-Ag system boasted the shortest start-up time, at only 100 h. An increase in the cell voltage during start-ups means an increase in the activity of electroactive bacteria, while providing nutrients (in wastewater). Whereas a decrease in the cell voltage during start-ups indicates a reduction in the activity of microorganisms due to the consumption of nutrients (wastewater was not replaced or replenished during a single start-up) [62]. A significant drop in the cell voltage suggested the need to replace the substrates (wastewater), and thus initiate the next start-up of the MFC [63].
This situation is because the cell is in the start-up process. Start-up is a process by which a biofilm (generating electricity) is slowly formed on the anode surface. As electricity-producing microorganisms acclimate and grow, they gradually outpace the growth rate of non-electricity-producing microorganisms [64]. Only when electricity-producing microorganisms become dominant and form a biofilm adhering to the anode surface is the electrode suitable for use as an anode in an MFC. Then the rate of consumption of organic matter increases and, as a result, the production of electricity increases in large quantities.
The GDE/Ni-Co and GDE/Cu-Ag systems, respectively, shortened the start-up time (during first start-up) by 38% and 52% compared with the GDE/Cu-B system, suggesting that using these systems (primarily the GDE/Cu-Ag system) could shorten the start-up time of MFCs (during first start-up). During the second start-up, the cell voltage increased relatively quickly, but the cell voltage value was not high (46 mV for GDE/Cu-Ag; 41 mV for GDE/Ni-Co; 33 mV for GDE/Ni-Co).
It should be noted that, during the third start-up, the cell voltage increased rapidly and significantly, reaching 182 mV for the GDE/Cu-Ag system, 141 mV for the GDE/Ni-Co system, and 127 mV for the GDE/Cu-B system. Therefore, after the third start-up, it was concluded that the electrodes were suitable for use in MFCs.
Next, the cell voltage of the MFCs in one cycle (after the third start-up) was measured. Measurements showed that after the third start-up, each subsequent start-up produced similar effects (characteristic of cell voltage curves). The measurements were performed, similar as for the first three start-ups, at a temperature of 25 °C. Figure 6 shows the cell voltage of the MFCs in one cycle (in fourth start-up).
As the data show, in one cycle (after the third start-up) the highest value (236 mV) was obtained for the GDE/Cu-Ag electrode system, and the lowest (186 mV) for the GDE/Cu-B system. Whereas, for the GDE/Ni-Co system, this was 193 mV. The cycle was considered completed after 150 h of MFC operation, when the cell voltage dropped below 40% of the highest value obtained in one cycle. In each electrode system, after the third start-up, the voltage increased rapidly, reaching maximum values after approximately 20 h of MFC operation. For the GDE/Cu-Ag system as well as GDE/Ni-Co system, relatively stable voltages were sustained for approximately 40 h. However, for the GDE/Cu-Ag system, after obtaining the maximum value, the voltage steadily decreased throughout the entire period of MFC operation. Whereas the average cell voltage obtained during one cycle (similar to the maximum voltage readings) reached the highest value for the GDE/Cu-Ag system and the lowest for the GDE/Cu-B system. Table 2 lists the average cell voltage values for the various electrode systems.
As the data show (Table 2), in one cycle (after the third start-up) the value of average cell voltage of the GDE/Cu-Ag system was 21% higher in comparison to the average cell voltage of the GDE/Ni-Co system, and 30% higher than the average cell voltage of the GDE/Cu-B system.
Subsequently, the power density achieved during MFC operation with different electrode systems was examined. Figure 7 shows power density curves obtained in the MFCs with GDE/Cu-Ag, GDE/Ni-Co and GDE/Cu-B electrode systems (in one cycle, during the fourth start-up).
As the external resistance decreases, the current density gradually rises, resulting in an increase in power density. Once the external and internal resistances converge, the power density peaks. However, subsequent internal polarization causes a decline in the power density despite an increase in current density [65]. The maximum power density was obtained in one cycle for the GDE/Cu-Ag system, whereas the lowest power density was obtained for the GDE/Cu-B system. The maximum power density for the GDE/Cu-Ag system (32 mW·m−2) was obtained at a current density of 250 mA·m−2, for the GDE/Ni-Co system at 200 mA·m−2, and for the GDE/Cu-B system at 150 mA·m−2. In the case of the GDE/Cu-Ag system, over 75% of the value power density was obtained in the range of 66% of the value of current density. For the GDE/Ni-Co system, over 79% of the value power density was obtained in the range of 50% of the value of current density. For the GDE/Cu-B system, over 80% of the value power density was obtained in the range of 42% of the value of current density. The power density in each case is low, but one reason for these values is the use of the MFC design. This is mainly because a chamber separator (sintered glass) was used. Table 3 lists the maximum power density values for the various electrode systems.
Next, the COD reduction was analyzed. Because the measurements were carried out during one cycle, it was not possible to analyze the concentration during MFC operation. Electrical measurements did not disturb the operation of the cell, so they could be carried out during the entire cycle. However, in the case of COD measurements, the concentration analysis was performed before flooding the MFC, and after a full MFC operation cycle. Figure 8 shows the COD reduction before, and after MFC operation.
In one cycle in the MFC, the reduction of COD was obtained or all measurements. In the case of the GDE/Cu-Ag system, there was over 52% of COD reduction, for GDE/Ni-Co, a COD reduction of over 38% was recorded, and for the GDE/Cu-B system, it was over 42%. Therefore, the highest COD reduction efficiency was achieved for the GDE/Cu-Ag system. The least effective reduction was recorded for the GDE/Ni-Co system. It is important to note, though, that the disparity in COD reductions between the MFCs using the GDE/Cu-B and GDE/Ni-Co systems is negligible. Overall, the COD reduction efficiency in one MFC operation cycle (about 150 h) for all electrode systems is high.
In summary, it should be stated that the GDE electrode, regardless of the electrode system (GDE/Cu-Ag, GDE/Ni-Co, and GDE/Cu-B), was ready for operation. In each case, a biofilm formed on the GDE electrode, which allowed bioelectricity to be obtained. The cell voltage and cell power density values were not high, but this was due to, among others, the used chamber separator or external load. The readiness of the GDE for operation was achieved after the third start-up, irrespective of the cathode used. The extended start-up duration can be attributed to the utilization of activated sludge microorganisms, which required time to develop a biofilm (containing the majority of EAB) on the GDE. The employment of microorganisms obtained from a previously operational MFC would likely expedite the start-up process and potentially enhance the cell voltage. Nonetheless, this study focuses on initiating MFCs with GDEs from the ground up. The subsequent phase of this research will involve measurements using microorganisms derived from the MFC utilized in this study.
In analyzing these electrode systems, it should be concluded that the GDE/Cu-Ag system outperformed all others, showcasing superior values across all electrical measurements including cell voltage, power density, and current density, while conversely, the GDE/Cu-B system demonstrated the least favorable results. Interestingly, the efficiency of COD reduction followed a similar trend (regarding the GDE/Cu-Ag system), with the GDE/Cu-Ag system demonstrating the highest efficiency, and the GDE/Ni-Co system showing the lowest.

4. Conclusions

In this study, the feasibility of using currently manufactured electrodes (intended for fuel cells) as anodes in MFCs was analyzed. This research was conducted for various electrode systems (anode-cathode: GDE/Cu-B, GDE/Ni-Co, and GDE/Cu-Ag). During this research, the start-up time, cell voltage, current density, cell power density, and COD reduction were measured. The average cell voltage obtained in the MFC depended on the electrode system and was 127 mV for GDE/Cu-B, 143 mV for GDE/Ni-Co, and 181 mV for GDE/Cu-Ag, respectively. The maximum power density in one cycle (after the third start-up) was 32 mW·m−2 at a current density of 250 mA·m−2 for the GDE/Cu-Ag electrode system. Moreover, for this electrode system, over 75% of the value power density was obtained in the range of 66% value of the current density. In the case of the COD measurements, the reduction of this parameter was obtained for all electrode setups. The highest COD reduction efficiency was achieved for the GDE/Cu-Ag system (52%). In the case of GDE/Ni-Co COD reduction, over 38% was recorded, and for the GDE/Cu-B system over 42%.
In summary, based on the measurement data, it was found that the GDE electrode can be used as the anode of the MFC. Moreover, the GDE electrode ensured biofilm formation, especially in the GDE/Cu-Ag electrode system. After three start-ups, the GDE electrode (with formed biofilm) was suitable for use in MFCs, and using a GDE electrode, it is possible to easily transfer it together with the formed biofilm to a new MFC.
The data obtained in this work will allow us to compare with the next planned works of using GDE as anode in MFCs. However, it is important to analyze the feasibility of eliminating the oxygen, fluorine, and sulfur from the anode (GDE) in order to make measurements and compare them with the results obtained without additional preparation. Subsequent research will focus also on the use of the working GDE (with formed biofilm) electrode in other MFCs designs.

Author Contributions

Conceptualization, P.P.W.; methodology, P.P.W.; investigation, P.P.W. and B.W.; data curation, P.P.W. and B.W.; writing—original draft preparation, P.P.W. and B.W.; writing—review and editing, P.P.W. and B.W.; visualization, P.P.W. and B.W.; supervision, P.P.W. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

No new data were created or analyzed in this study. Data sharing is not applicable to this article.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Principles of operation of the microbial fuel cell.
Figure 1. Principles of operation of the microbial fuel cell.
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Figure 2. View of the electrodes: (A) GDE (anode), from the side of the deposited electrode layer and from the side of the matrix (steel mesh); (B) copper mesh (cathode) for catalyst deposition.
Figure 2. View of the electrodes: (A) GDE (anode), from the side of the deposited electrode layer and from the side of the matrix (steel mesh); (B) copper mesh (cathode) for catalyst deposition.
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Figure 3. The scheme and view of the MFC used in research: 1—air supply, 2—carbon dioxide outflow, 3—wastewater, 4—GDE, 5—cathode chamber, 6—cover closing the anode chamber, 7—cathode, 8—sintered glass chamber separator, 9—electrical measurements, 10—COD reduction analysis, R—external load.
Figure 3. The scheme and view of the MFC used in research: 1—air supply, 2—carbon dioxide outflow, 3—wastewater, 4—GDE, 5—cathode chamber, 6—cover closing the anode chamber, 7—cathode, 8—sintered glass chamber separator, 9—electrical measurements, 10—COD reduction analysis, R—external load.
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Figure 4. Enlarged view of the gas diffusion electrode surface, and chemical composition of the electrode.
Figure 4. Enlarged view of the gas diffusion electrode surface, and chemical composition of the electrode.
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Figure 5. Cell voltage during consecutive MFC start-ups, for three different electrode systems (GDE/Cu-Ag, GDE/Ni-Co and GDE/Cu-B).
Figure 5. Cell voltage during consecutive MFC start-ups, for three different electrode systems (GDE/Cu-Ag, GDE/Ni-Co and GDE/Cu-B).
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Figure 6. Output cell voltage in one cycle (after 3 start-ups).
Figure 6. Output cell voltage in one cycle (after 3 start-ups).
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Figure 7. Power density curves obtained during MFC operation.
Figure 7. Power density curves obtained during MFC operation.
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Figure 8. COD reduction in MFCs with various electrode configurations in the relation to the MFC operating time. Measurement of COD when the cathode chamber was flooded with wastewater and after one full MFC operation cycle.
Figure 8. COD reduction in MFCs with various electrode configurations in the relation to the MFC operating time. Measurement of COD when the cathode chamber was flooded with wastewater and after one full MFC operation cycle.
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Table 1. Formulation of the mixture utilized for catalyst deposition [49].
Table 1. Formulation of the mixture utilized for catalyst deposition [49].
AlloyComponentVolume [mol·L−1]
Cu-AgAgNO30.02
CuSO4·7H2O0.05
Trilon B0.12
NaOH1.00
Ni-CoNiSO4 × 7H2O0.92
CoSO4 × 7H2O0.07
H3BO31.03
NaCl0.25
Cu-BNaBH40.02
CuSO4·7H2O0.05
NaOH1.00
Trilon B0.12
Table 2. Average cell voltage of MFC for various electrodes systems (in one cycle after 3 start-ups).
Table 2. Average cell voltage of MFC for various electrodes systems (in one cycle after 3 start-ups).
Electrode SystemAverage Cell Voltage
[mV]
GDE/Cu-Ag181
GDE/Ni-Co143
GDE/Cu-B127
Table 3. Maximum power density of MFC for various electrodes.
Table 3. Maximum power density of MFC for various electrodes.
Electrode SystemMaximum Power Density
[mW·m−2]
GDE/Cu-Ag32
GDE/Ni-Co24
GDE/Cu-B20
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Włodarczyk, P.P.; Włodarczyk, B. Study of the Use of Gas Diffusion Anode with Various Cathodes (Cu-Ag, Ni-Co, and Cu-B Alloys) in a Microbial Fuel Cell. Energies 2024, 17, 1636. https://doi.org/10.3390/en17071636

AMA Style

Włodarczyk PP, Włodarczyk B. Study of the Use of Gas Diffusion Anode with Various Cathodes (Cu-Ag, Ni-Co, and Cu-B Alloys) in a Microbial Fuel Cell. Energies. 2024; 17(7):1636. https://doi.org/10.3390/en17071636

Chicago/Turabian Style

Włodarczyk, Paweł P., and Barbara Włodarczyk. 2024. "Study of the Use of Gas Diffusion Anode with Various Cathodes (Cu-Ag, Ni-Co, and Cu-B Alloys) in a Microbial Fuel Cell" Energies 17, no. 7: 1636. https://doi.org/10.3390/en17071636

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