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Morphology observation of GAC using SEM analysis at varying average sizes of particles 309 of (a) 2-3 mm, (b) 0.6-1.1 mm, and (c) 0.45-0.6 mm. 310
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Microbial fuel cell (MFC) architectural modification is increasingly becoming an important area of research due to the need to improve energy recovery. This study presents a low-cost modification method of the anode that does not require pre-treatment-step involving hazardous chemicals to improve performance. The modification step involves depositi...
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... variation based experiments were initially conducted using a carbon cloth without 185 GAC at pH 6 and by using a salt bridge as a separator. Results in Fig. 2a were adapted from 186 polarization and power output curves in Fig. S5. The results represent the output voltage and 187 current output observed at maximum achieved power output (Fig. 2a). Increase in temperature 188 from 25 °C to 35 °C led to an increase in achieved output voltage (from 29.1 mV to 31.9 mV), 189 current output (from 145.2 mA m -3 to 159.5 mA m -3 ) and maximum power output (from 4.2 mW ...
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... power output of 235.4 mW m -3 at 297 a current output of 1085.2 mA m -3 . In addition, when the average size of particles was increased 298 above the range of 0.6-1.1 mm, a performance decrease was also observed. 299 The observations in Fig. 4 can be explained when the morphology of the GAC and the 304 bacterial attachment is considered in Fig. 5 The GAC of an average size of particles of 2-3 mm had a skeletal morphology as shown in 311 Fig. 5a. Skeletal structure then began to disappear with decrease in particle size as shown in Fig. 312 5b and Fig. 5c. The attachment of the bacteria is shown in blue squares depicted in micrograms 313 of Fig. 5a and Fig. 5b. However, as it can ...
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... the average size of particles was increased 298 above the range of 0.6-1.1 mm, a performance decrease was also observed. 299 The observations in Fig. 4 can be explained when the morphology of the GAC and the 304 bacterial attachment is considered in Fig. 5 The GAC of an average size of particles of 2-3 mm had a skeletal morphology as shown in 311 Fig. 5a. Skeletal structure then began to disappear with decrease in particle size as shown in Fig. 312 5b and Fig. 5c. The attachment of the bacteria is shown in blue squares depicted in micrograms 313 of Fig. 5a and Fig. 5b. However, as it can be seen in Fig. 5c, there was no effective attachment of 314 bacteria that was seen in average size ...
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... observed. 299 The observations in Fig. 4 can be explained when the morphology of the GAC and the 304 bacterial attachment is considered in Fig. 5 The GAC of an average size of particles of 2-3 mm had a skeletal morphology as shown in 311 Fig. 5a. Skeletal structure then began to disappear with decrease in particle size as shown in Fig. 312 5b and Fig. 5c. The attachment of the bacteria is shown in blue squares depicted in micrograms 313 of Fig. 5a and Fig. 5b. However, as it can be seen in Fig. 5c, there was no effective attachment of 314 bacteria that was seen in average size of particles of 0.45-0.6 mm. ...
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... 304 bacterial attachment is considered in Fig. 5 The GAC of an average size of particles of 2-3 mm had a skeletal morphology as shown in 311 Fig. 5a. Skeletal structure then began to disappear with decrease in particle size as shown in Fig. 312 5b and Fig. 5c. The attachment of the bacteria is shown in blue squares depicted in micrograms 313 of Fig. 5a and Fig. 5b. However, as it can be seen in Fig. 5c, there was no effective attachment of 314 bacteria that was seen in average size of particles of 0.45-0.6 mm. ...
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... attachment is considered in Fig. 5 The GAC of an average size of particles of 2-3 mm had a skeletal morphology as shown in 311 Fig. 5a. Skeletal structure then began to disappear with decrease in particle size as shown in Fig. 312 5b and Fig. 5c. The attachment of the bacteria is shown in blue squares depicted in micrograms 313 of Fig. 5a and Fig. 5b. However, as it can be seen in Fig. 5c, there was no effective attachment of 314 bacteria that was seen in average size of particles of 0.45-0.6 mm. ...
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... The GAC of an average size of particles of 2-3 mm had a skeletal morphology as shown in 311 Fig. 5a. Skeletal structure then began to disappear with decrease in particle size as shown in Fig. 312 5b and Fig. 5c. The attachment of the bacteria is shown in blue squares depicted in micrograms 313 of Fig. 5a and Fig. 5b. However, as it can be seen in Fig. 5c, there was no effective attachment of 314 bacteria that was seen in average size of particles of 0.45-0.6 mm. ...
Citations
... In addition, they do not meet the required properties of electrode materials in terms of chemical stability for long-term operation [31]. Therefore, numerous studies on air cathodes have been proposed to improve the output performance of MFCs while reducing their capital cost [35,42,47,56,73]. ...
... MFC-based air cathodes can be divided into a floating air cathode, an aqueous air cathode, and a wick air cathode due to the differences in cathode assembly. Due to its simple structure and direct utilization of atmospheric oxygen as the final electron acceptor, it is considered a practical and sustainable system [11,35,46,47,63]. This shows that improving cathode efficiency is one of the most effective ways to increase MFC performance [23,80]. ...
Sediment microbial fuel cells (SMFC) are a potential alternative for benthic sediment remediation in bioelectricity generation. The cathodic oxygen reduction rate is an important limiting factor in SMFC. This study aims to evaluate the effects of submerged and floating cathodes on bioelectricity generation and benthic nutrient removal in SMFC. Based on the generated current density, SMFC with a wick-air cathode, 10 cm from the top sediment surface and partially submerged in water and exposed to air (SMFC-CW) was found to be superior to those with bottom cathode, 1 cm from the top sediment surface (SMFC-C1), a middle cathode, 5 cm from the top sediment surface (SMFC-C5), and a floating cathode, 10 cm from the top sediment surface and placed under the overlying surface water (SMFC-C10). In the polarization test, SMFC-CW contributed to the lowest concentration loss with a maximum current density of 236.4 mA/m2. The overshoot phenomenon in SMFC-C1 is not a good indicator of the SMFC system, despite the generation of a high maximum power density. This study has shown that a large pH difference between the anodic and cathodic regions in SMFC-CW is important for bioelectricity generation as it was observed that the internal resistance of SMFCs changes. SMFC-CW showed the largest reduction in phosphate concentration, from 0.61 mg/L to 0.14 mg/L. These results provide a simple strategy for sustainable bioelectricity generation in SMFC systems while remediating benthic sediments.
... The thickness, porosity, and surface area-to-volume (SAV) ratio of the ceramic and the performance of fine-fired clay affected the overall MFC performances. Better fuel mass transfer and lower resistance are achieved with a higher SAV of the reactor [44]. ...
... As a result, the generated power density is inversely proportional to the size of a single microbial fuel cell when scaled up [133]. The increasing biofilm deposition caused the internal resistance to rise and an edge effect, which could explain why the generated power density was drastically reduced by increasing the current-limiting anodic area [44,126,134]. The rise in internal resistance (ohmic overvoltage) restricts both the transport of electrons between electrodes and the transfer of ions between chambers and in the electrolyte [135]. ...
... These methods include the application of mediators [168], electrode modification with catalysts [137], and cathodic compartment operational condition optimisation [169]. Additionally, by increasing the electrode's surface area [44], enhancing catalysis [170,171], raising the temperature [172], and creating an enriched electro-active biofilm on the electrode's surface [110], reduced activation losses [173] can be attained in the anode. Substrate crossover in the cathode compartment has a negative impact on the MFC's performance [174]. ...
Microbial fuel cell (MFC) is a sustainable and renewable technology for applications in power engineering and wastewater treatment. In double chamber MFC, the anode and cathode are separated by a selective membrane, which reduces oxygen transfer, substrate losses and keeps the anode chamber anaerobic. The high price of commercially available membranes, proton exchange membrane (PEM) has accelerated research into substitute materials for use as separators in MFC. Various research identifies low-cost clay-based ceramic materials as one of the most promising substitutes for commercial membranes. These low-cost materials are a viable option for spiked systems due to their low cost, functional long-term robustness, and natural availability. These eco-friendly materials' ability to easily change their microstructure by mixing various compounds into the ceramic raw clay is another benefit of employing them as membranes. The MFC ceramic also ensures stable power output for up to nineteen months in terms of long-term performance reported by previous studies demonstrated a performance of up to 1.56 mW (22.3 W m − 3) over a one-year period. The 3-module cascade achieved up to 75 mW (13.9 W m − 3) of power, indicating 20 % power loss on day 446, the stack module with 22 MFCs obtained up to 21.4 mW (11.9 W m − 3). In the pilot-scale and industrial applications of MFC, the emphasis should not only be on the greatest energy harvesting or recovery but also on the large-scale MFC prototype's economic viability. This review discusses the use of ceramics in MFC for low-cost ceramics, with long-term performance, upscaled, stacked, pilot plant and the challenges of their use in MFC.
... This was done by cutting the carbon cloth to size, depositing the GAC inside the anode carbon cloth, and using a sewing thread to form an enclosure and to ensure that the activated carbon granules do not fall out. This was done to increase the appropriate surface area for cell attachment [19]. The cathode was only made of a carbon cloth with a surface area of 1130 cm 2 . ...
Development of upflow microbial fuel cells (MFCs) is of importance since these types of MFCs can be integrated in wastewater treatment plants for the provision of continuous treatment and energy recovery. In this study, key operational parameters were assessed for a hexavalent chromium [Cr(VI)] reducing annular upflow MFC (approximately 5 L total liquid volume). The optimized operational parameters were cathode and anode hydraulic retention times of 2 days, temperature of 34 • C, influent Cr(VI) concentration of 800 mg L − 1 , and anode and cathode pH of 7 and 4 respectively. This study demonstrated that a parallel configuration is advantageous since it leads to a high current and power density operation due to low internal resistance when compared to series configuration. The precipitation of Cr(III) over time was demonstrated to have a potential to reduce MFC performance and operating at high influent Cr(VI) pHs (7-10) should be avoided. The optimized peak output potential difference and maximum power density achieved under parallel configuration were 896 mV and 994 mW m − 3 respectively, at a current density of 1191 mA m − 3. This study provides a step into developing continuous metal reducing MFCs for use in simultaneous treatment of heavy metals in wastewater and energy recovery.
... The fuel cell is a device that employs electrochemical processes to transform chemical energy into electrical energy. According to Matsena, Mabuse, Tichapondwa, and Chirwa [11], the use of graphene in fuel cells has shown enhanced performance via the augmentation of electrode surface area, enhancement of electrical conductivity, and reduction of device resistance [12]. A demonstration has shown advancements in the efficiency, durability, and stability of fuel cells using graphene as the basis material [13,14]. ...
Graphene, a two-dimensional carbon-based material, holds significant promise for elevating the performance of energy storage technologies such as batteries, supercapacitors, and fuel cells. This review article aims to present the latest advancements in utilizing graphene for energy storage devices, with a focus on developments occurring in the past few months. These advancements involve the integration of graphene-based materials into the device designs to augment their efficiency, longevity, and stability, ultimately driving the evolution of advanced energy storage systems. Realizing graphene's full potential as an energy storage material and comprehending its intrinsic properties necessitate further in-depth investigation. Achieving a comprehensive understanding of graphene is imperative before fully harnessing its capabilities in this field.
... Among various types of carbon materials, activated carbon (AC) is a cost-effective and promising material capable of enhancing electron transfer and power generation. Compared to granulated and nonactivated carbon, AC has an extensive surface area and a highly developed pore distribution structure, which facilitates bacterial attachment and biofilm development [30,31]. In addition, AC was reported to accelerate electron transfer between the bacterial layers in the bacterial anode towards the anode material, which serves as a current collector [32][33][34]. ...
... Decreasing the average GAC particle size resulted in lower MFC electroactivity performance. The power density output of the control anode (without GAC) was only 344.9 mW‧m − 3 [30] investigate using activated carbon nanofiber nonwoven (ACNFN) as a novel anode for MFC and compare its performance with two commonly used anodes in MFC: carbon cloth (CC) and granular activated carbon (GAC). The power density obtained from ACNFN (758 W‧m − 3 ) was dramatically higher than that obtained by the CC and GAC (161 and 3.4 W‧m − 3 , respectively) [47]. ...
The bacterial anode is a key factor for microbial fuel cell (MFC) performance. This study examined the potential of kaolin (fine clay) to enhance bacteria and conductive particle attachment to the anode. The bio-electroactivity of MFCs based on a carbon-cloth anode modified by immobilization with kaolin, activated carbon, and Geobacter sulfurreducens (kaolin-AC), with only kaolin (kaolin), and a bare carbon-cloth (control) anodes were examined. When the MFCs were fed with wastewater, the MFCs based on the kaolin-AC, kaolin, and bare anodes produced a maximum voltage of 0.6 V, 0.4 V, and 0.25 V, respectively. The maximum power density obtained by the MFC based on the kaolin-AC anode was 1112 mW‧m-2 at a current density of 3.33 A‧m-2, 12% and 56% higher than the kaolin and the bare anodes, respectively. The highest Coulombic efficiency was obtained by the kaolin-AC anode (16%). The relative microbial diversity showed that Geobacter displayed the highest relative distribution of 64% in the biofilm of the kaolin-AC anode. This result proved the advantage of preserving the bacterial anode exoelectrogens using kaolin. To our knowledge, this is the first study evaluating kaolin as a natural adhesive for immobilizing exoelectrogenic bacteria to anode material in MFCs.
... The higher power output was attributed to the better interaction with microorganisms and less mass transfer limitation. Matsena et al. [37] improved the performance of anode electrode in a microbial fuel cell through deposition of granular activated carbon on carbon cloth. Using the granular particle size of 0.6-1.1 mm, available surface area increased significantly that facilitated the attachment of cell to the surface; however, at higher surface area (with large size particles), MFC performance reduced from 1300 mW.m −3 at particle size 0.6 mm to 900 mW.m −3 at particle size 1.1 mm, concluding that anode surface area needs optimization to achieve the highest MFC performance. ...
In microbial fuel cells, the surface areas of electrodes play a key role in power generation. Conventionally, the surface area ratio of 1 is considered, but it is neither electrochemically optimized nor economically justified. This study seeks the optimized ratio of Aan/Aca. in a double-chamber air-cathode pure-culture microbial fuel cell. Four different anode electrode surface areas were considered in four pure-culture air-cathode MFCs with the Aan/Aca. ratios of 0.4, 0.6, 0.8, and 1. Electrochemical impedance spectroscopy (EIS) indicates that as the Aan/Aca. ratio increases, total internal resistance decreases from 117.54 Ω to 42.03 Ω in which the share of substrate oxidation resistance ranges from 98% at the ratio of 0.4 to 86% at the ratio of 1. Tafel plot also indicates that exchange current increases from 3.76 mA to 19.27 mA as the anode surface increases suggesting higher reaction rates at higher ratios. The polarization test demonstrates that power output does not follow total resistance pattern and that maximum power density (based on the cathode surface) of 41.67 ± 2.08 mW.m⁻² occurs at the Aan/Aca. ratio of 0.6. Also, the highest operating current of 1.17 mA is recorded at the Aan/Aca. ratio of 0.6 after 90 days of operation. These observations suggest that there is an optimum Aan/Aca. ratio of 0.6 in which the charge transfer rate is maximum and substrate oxidation rate is minimum. The results also suggest that there is a correlation between power output and Aan/Aca. ratio that predicts the optimum ratio of 0.68 where power output is maximum.
Graphical Abstract
... mm resulted in a decrease in MFC performance of an output voltage of 75 mV and a maximum power output of 28 mW m -3 at a current output of 375 mA m -3 . The average size of particles of 0.6-1.1 mm led to improved performance due to better attachment and the retention of bacteria since the surface is rough and irregular (Matsena et al., 2021b). Furthermore, the reason for performance deterioration for the average size particles of 0.45-0.6 ...
... Furthermore, the reason for performance deterioration for the average size particles of 0.45-0.6 mm is because there is a significant reduction in bacterial attachment due to lack of porosity (Matsena et al., 2021b). ...
Microbial Fuel Cell (MFC) technology provides the potential of utilising wastewater treatment plants as power generation units. The biogenic bacteria cultures used in this study were collected from marine environment in South Africa (Saldanha Bay, South Africa). The MFC was configured to operate without a cathode chamber using an air-cathode configuration. Biological deposition of Pd(0) nanoparticles was used to improve the electrocatalytic activity of the anode. Solid material such as a carbon rod has a low surface area compared to dispersed material such as granular activated carbon (GAC) when using the same amount of mass. Therefore, GAC is a viable replacement to solid material anode electrodes which is proposed to improve MFC performance since the anode surface area plays a crucial role in MFCs. The use of parallel configuration is proposed in this study since it leads to a high current and power density operation.
... When GAC is used in MFCs, two phenomena can occur: (i) the electroactive biofilm releases electrons during the oxidation of organics, and (ii) these electrons are stored at the pore surface of the carbon, while cations are required to maintain the charge balance in the EDL [17,24]. Using this concept, GAC has previously been used in the anode of MFCs to form a capacitive bioanode enhancing the performance of MFCs [15,22,24,25]. Liu et al. 2020 reported that integration of GAC in the anode chamber provides a larger surface area for the growth of exoelectrogenic bacteria at the anode, improving the power output as well as decreasing the internal resistance of the system. ...
Nitrate (NO3−-N) and nitrites (NO2−-N) are common pollutants in various water bodies causing serious threats not only to aquatic, but also to animals and human beings. In this study, we developed a strategy for efficiently reducing nitrates in microbial fuel cells (MFCs) powered by a granular activated carbon (GAC)-biocathode. GAC was developed by acclimatizing and enriching denitrifying bacteria under a redox potential (0.3 V) generated from MFCs. Thus, using the formed GAC-biocathode we continued to study their effect on denitrification with different cathode materials and circulation speeds in MFCs. The GAC-biocathode with its excellent capacitive property can actively reduce nitrate for over thirty days irrespective of the cathode material used. The stirring speed of GAC in the cathode showed a steady growth in potential generation from 0.25 V to 0.33 V. A rapid lag phase was observed when a new carbon cathode was used with enriched GAC. While a slow lag phase was seen when a stainless-steel cathode was replaced. These observations showed that effective storage and supply of electrons to the GAC plays a crucial role in the reduction process in MFCs. Electrochemical analysis of the GAC properties studied using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and zeta potential showed distinct properties with different abiotic and biocathode conditions. We found that the enrichment of electrotrophic bacteria on GAC facilitates the direct electron transfer in the cathode chamber for reducing NO3−-N in MFCs as observed by scanning electron microscopy.
... Figure 4 shows the micrographs of the oxidized materials. The 1h (AC-1h) and the 2 h (AC-2h) oxidized carbon presented a change in the morphology, with a more irregular surface and an increase in the pore diameter; likewise, a skeletal morphology [27] in the material with a 2 h oxidation is observed. The change in morphology is directly related to the chemical oxidation with HNO3 [28], as the acid in contact with the material modified the textural properties, increasing the surface porosity due to the carbon bonds' degradation. ...
Many adsorbent materials are now commercially available; however, studies have focused on modifying them to enhance their properties. In this study, an activated carbon (AC) and hydroxyapatite (HAp) composite was synthesized by the immersion of ACs in a simulated body fluid solution, varying the AC oxidation degree along with the addition of CaSiO3. The resulting composites were characterized by ash %, X-ray fluorescence (XRF), Fourier-transformed infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and point of zero charge (PZC). The characterization results indicated that the addition of CaSiO3 and the oxygenated functional groups in the AC surface are key factors for HAp growth. The composites were tested on methylene blue (MB) adsorption as a potential application for the synthesized materials. Adsorption isotherms were modeled with Langmuir and Freundlich isotherms, and the composites were fitted to a Langmuir model with the highest qmax value of 9.82. The kinetic results indicated that for the pseudo-second-order model, the composites fitted, with a contact time of 180 min to remove a 95.61% average of the MB. The results indicate that composite materials can be an efficient adsorbent for the removal of MB from aqueous solutions at low concentrations since the material with the highest amount of HAp growth removed 99.8% of the MB in 180 min.
... Despite the high ORR activity of PGM materials, alternative electrocatalysts have been developed. Carbon-based metal-free catalysts have been explored to replace PGM materials at the cathode side of MFCs, including activated carbon [15][16][17][18][19], graphene oxide [20,21], and biochar [22][23][24][25][26][27]. Along with low cost, they possess suitable properties such as good mechanical strength, high electronic conductivity, high surface area associated with a relatively good ORR activity at neutral pH. ...
This work reports the development of an iron-nitrogen-carbon electrocatalyst (Fe-N-C) synthesized by functionalization of a carbon support using low-cost Fe- and N-based precursors in a wet impregnation procedure followed by a pyrolysis treatment under inert atmosphere. Structure and surface chemistry were investigated by Raman and X-ray photoelectron spectroscopy (XPS), which indicated an efficient interaction of precursors with the carbon support during the wet-impregnations step, which allows obtaining a carbonized material with a high content of active sites based on Fe-Nx moieties. This led to a Fe-N-C materials with high catalytic activity towards oxygen reduction at neutral pH, as demonstrated by cyclic voltammetry (CV) and hydrodynamic linear sweep voltammetry with rotating ring disk electrode (LSV-RRDE). The Fe-N-C electrocatalyst was incorporated in air-breathing cathodes which performance was optimized in terms of oxygen reduction activity and stability. Such cathodes were assembled in a single-chamber microbial fuel cell prototypes, which electrical power and voltage generation was evaluated over time.
