Bio-cathode materials evaluation in microbial fuel cells: A comparison of graphite felt,carbon paper and stainless steel mesh materials

The choice of the cathode material is crucial for every bio-cathode microbial fuel cell (MFC) setup. The commonly used biocathode materials, Graphite felt (GF), carbon paper (CP) and stainless steel mesh (SSM) were compared and evaluated in terms of current density, power density, and polarization. The maximum current density and power density of the MFC with GF-biocathode achieved 350 mA m⁻² and 109.5 mW m⁻², which were higher than that of the MFC with CP-biocathode (210 mA m⁻² and 32.7 mW m⁻²) and the MFC with SSM-biocathode (18 mA m⁻² and 3.1 mW m⁻²). The polarization indicated that the biocathode was the limiting factor for the three MFC reactors. Moreover, cyclic voltammetry (CV) showed that the microorganisms on the biocathode played a major role in oxygen reduction reaction (ORR) for GF- and CP-biocathode but SSM-biocathode. Electrochemical impedance spectroscopy suggested that GF biocathode performed better catalytic activity toward ORR than that of CP- and SSM-biocathode, also supported by CV test. Additionally, the MFC with GF-biocathode had the highest Coulombic Efficiency. The results of this study demonstrated GF was the most suitable biocathode for MFCs application among the three types of materials when using anaerobic sludge as inoculums.     

Improved performance of microbial fuel cell using combination biocathode of graphite fiber brush and graphite granules

The efficiency and sustainability of microbial fuel cell (MFC) are heavily dependent on the cathode performance. We show here that the use of graphite fiber brush (GBF) together with graphite granules (GGs) as a basal material for biocathode (MFC reactor type R1) significantly improve the performance of a MFC compared with MFCs using GGs (MFC reactor type R2) or GFB (MFC reactor type R3) individually. Compared with R3, the use of the combination biocathode (R1) can shorten the start-up time by 53.75%, improve coulombic efficiencies (CEs) by 21.0 ± 2.7% at external resistance (R_EX) of 500 Ω, and increase maximum power densities by 38.2 ± 12.6%. Though the start-up time and open circuit voltage (OCV) of the reactor R2 are similar to R1, the CE (R_EX = 500 Ω) and maximum power density of R2 are 21.4 ± 1.7% and 38.2 ± 15.6% lower than that of R1. Fluorescence in situ hybridization (FISH) analyses indicate the bacteria on cathodes of R1 and R2 are richer than that of R3. Molecular taxonomic analyses reveal that the biofilm formed on the biocathode surface is dominated by strains belonging to Nitrobacter, Achromobacter, Acinetobacter, and Bacteroidetes. Combination of GFB and GGs as biocathode material in MFC is more efficient and can achieve sustainable electricity recovery from organic substances, which substantially increases the viability and sustainability of MFCs.     

Mesh optimization for microbial fuel cell cathodes constructed around stainless steel mesh current collectors

Mesh current collectors made of stainless steel (SS) can be integrated into microbial fuel cell (MFC) cathodes constructed of a reactive carbon black and Pt catalyst mixture and a poly(dimethylsiloxane) (PDMS) diffusion layer. It is shown here that the mesh properties of these cathodes can significantly affect performance. Cathodes made from the coarsest mesh (30-mesh) achieved the highest maximum power of 1616 ± 25 mW m⁻² (normalized to cathode projected surface area; 47.1 ± 0.7 W m⁻³ based on liquid volume), while the finest mesh (120-mesh) had the lowest power density (599 ± 57 mW m⁻²). Electrochemical impedance spectroscopy showed that charge transfer and diffusion resistances decreased with increasing mesh opening size. In MFC tests, the cathode performance was primarily limited by reaction kinetics, and not mass transfer. Oxygen permeability increased with mesh opening size, accounting for the decreased diffusion resistance. At higher current densities, diffusion became a limiting factor, especially for fine mesh with low oxygen transfer coefficients. These results demonstrate the critical nature of the mesh size used for constructing MFC cathodes.     

Improved performance of a tubular microbial fuel cell with a composite anode of graphite fiber brush and graphite granules

In this study, a composite electrode combined of a graphite fiber brush and carbon granules (MFC-GFB/GG) was adopted as the anode of a tubular microbial fuel cell (MFC). Compared with an MFC with graphite granules (MFC-GG) and an MFC with a graphite fiber brush (MFC-GFB), MFC-GFB/GG showed a longer lag time during the start-up process, while it reached the highest operating voltage at 50 Ω. Furthermore, during the stable operation, the MFC-GFB/GG achieved the highest power density of 66.9 ± 1.6 W m⁻³, which was about 5.3 and 1.2 times as that of MFC-GG and MFC-GFB, respectively. The highest performance of the MFC-GFB/GG can be attributed to the highest active biomass content on the electrode and the smallest internal resistance of the MFC. The optimum COD concentration was found to be 500 mg COD L⁻¹ for MFC-GFB/GG.     

Improve 3D electrode materials performance on electricity generation from livestock wastewater in microbial fuel cell

Swine wastewater that is collected from animal husbandry has organic high ammonia nitrogen. In this study, swine wastewater is converted into electrical energy using microbial fuel cells (MFCs). Carbon fibers are respectively combined with zinc-coated metallic wires or stainless steel wires in order to form different laminated electrodes, whose influence on the electricity generation of MFCs is then examined. The 3D laminated FN/carbon composites are used as electrodes, the stable electricity voltage is 291 mV and the COD removal efficiency reaches 81％. In contrast, SS/carbon composites only contribute to a stable electricity voltage of 12.3 mV and COD removal efficiency of 33%. Based on the surface contact angle test and the scanning electron microscopy (SEM) observation, the laminated FN/carbon composites have greater hydrophilicity and wettability than the laminated SS/carbon composites, and thus have a positive influence on the electricity generation of MFCs.     

Modification of graphite felt using nano polypyrrole and polythiophene for microbial fuel cell applications-a comparative study

Microbial fuel cells (MFC) are bio-electrochemical devices used for the generation of electricity from biomass. A single chamber membrane less air-breathing cathode microbial fuel cell (SCMFC) with two different anode configurations was investigated for energy generation using shewanella putrifaciens as bio-catalyst. The graphite felt (GF) anode was modified with 0.008 g/cc polypyrrole nanoparticles (Ppy-NPs) and 0.024 g/cc polythiophene nanoparticles (PTh-NPs) by conventional method. The nanoparticles coating improved the properties such as thermal characteristics and electron transfer capabilities of the anodes, which was confirmed by Thermogravimetric analysis (TGA), electrochemical impedance spectroscopy (EIS) and cyclic voltametry (CV). The variation in the cell potential with time under open circuit condition resulted in voltages of 0.842V and 0.644 V for Ppy-NP and PTh-NP modified GF respectively. A maximum power density (1.22 W/m²) was obtained for Ppy-NP modified GF than PTh-NP modified GF (0.8 W/m²). The results showed that GF coated with nano conductive polymers such as Ppy and PTh are the promising candidates for the best performance of a MFC.     

Biocatalyzed hydrogen production in a continuous flow microbial fuel cell with a gas phase cathode

A single liquid chamber microbial fuel cell (MFC) with a gas-collection compartment was continuously operated under electrically assisted conditions for hydrogen production. Graphite felt was used for anode construction, while the cathode was made of Pd/Pt coated Toray carbon fiber paper with a catalyst loading of 0.5 mg cm⁻². To achieve hydrogen production, the MFC was connected to a power supply and operated at voltages in a range of 0.5–1.3 V. Either acetate or glucose was used as a source of carbon. At an acetate load of 1.67 g (L_A d)⁻¹, the volumetric rate of hydrogen production reached 0.98 L_STP (L_A d)⁻¹ when a voltage of 1.16 V was applied. This corresponded to a hydrogen yield of 2 mol (mol-acetate)⁻¹ with a 50% conversion efficiency. Throughout the experiment, MFC efficiency was adversely affected by the metabolic activity of methanogenic microorganisms, which competed with exoelectrogenic microorganisms for the carbon source and consumed part of the hydrogen produced at the cathode.     

The use and optimization of stainless steel mesh cathodes in microbial electrolysis cells

Microbial electrolysis cells (MECs) provide a high-yield method for producing hydrogen from renewable biomass. One challenge for commercialization of the technology is a low-cost and highly efficient cathode. Stainless steel (SS) is very inexpensive, and cathodes made of this material with high specific surface areas can achieve performance similar to carbon cathodes containing a platinum catalyst in MECs. SS mesh cathodes were examined here as a method to provide a higher surface area material than flat plate electrodes. Cyclic voltammetry tests showed that the electrochemically active surface area of certain sized mesh could be three times larger than a flat sheet. The relative performance of SS mesh in linear sweep voltammetry at low bubble coverages (low current densities) was also consistent with performance on this basis in MEC tests. The best SS mesh size (#60) in MEC tests had a relatively thick wire size (0.02 cm), a medium pore size (0.02 cm), and a specific surface area of 66 m²/m³. An applied voltage of 0.9 V produced a high hydrogen recovery (98 ± 4%) and overall energy efficiency (74 ± 4%), with a hydrogen production rate of 2.1 ± 0.3 m³H₂/m³d (current density of 8.08 A/m², volumetric current density of 188 ± 19 A/m³). These studies show that SS in mesh format shows great promise for the development of lower cost MEC systems for hydrogen production.     

Hydrogen production from macroalgae by simultaneous dark fermentation and microbial electrolysis cell with surface-modified stainless steel mesh cathode

An affordable cathode material for microbial electrolysis cells (MECs) was synthesized via surface-modification of stainless steel mesh (SSM) by anodization. The anodization parameters, such as wire mesh size, temperature, applied voltage, operating time, were optimized. The surface-modified SSM (smSSM) exhibited porous surface and higher specific surface area. The as synthesized smSSMs were utilized as freestanding cathodes in a conventional microbial electrolysis cell (MEC) and a simultaneous dark fermentation and MEC process (sDFMEC). The H₂ production in MEC and sDFMEC with smSSM as cathode was approximately 150% higher than that with SSM. The performance of smSSM was 67–75% of that of Pt/C. The sDFMEC with smSSM as cathode was stable for 12 cycles of fed-batch operation in 60 days. Overall, energy conversion from S. japonica by sDFMEC was as high as 23.4%.     

Tubular ceramic performance as separator for microbial fuel cell: A review

The depletion of unsustainable conventional energy sources and global warming issues create world demand for green energy sources. The microbial fuel cell (MFC) technology with the capability to convert environmental waste to energy can be improved with cheap ceramic material. The ceramic is structurally porous, thus allow a direct exchange of cation. The ceramic material also enhances stability thermally and chemically, non-ion selective characteristic, high mechanical strength, and easily washable. Commercially produced ceramic structures have been proven to reduce Chemical Oxygen Demand up to 92% and allow high power output. It is also comparatively durable in the long-term operation of MFC, compared to the commercially available membrane. The novelty of using tubular design is the efficient use of space, which leads to the possibility of scaling up. As a conclusion, a combination of both ceramic material and tubular design could be an excellent alternative separator for MFC.     

The effect of nitric acid,ethylenediamine, and diethanolamine modified polyaniline nanoparticles anode electrode in a microbial fuel cell

Anode materials are important in the power generation of microbial fuel cell. In this study, polyaniline was used as a conducting polymer anode in two chambers MFC. XPS and SEM were used for the characterization of functional groups of anode materials and the morphology. The power generation of microbial fuel cell was elevated by the modification of anode by nitric acid, ethylenediamine, and diethanolamine. The time that MFC reaches its maximum power generation was shortened by modification. Moreover the SEM photos prove that, it causes better attachment of microorganisms as biocatalysts on electrode surface. The best performance of among the MFCs with different anode electrodes, was the system working by polyaniline modified by ethylenediamine as that generated power of 136.2 mW/m² with a 21.3% Coulombic efficiency.     

Unveiling characteristics of dye-bearing microbial fuel cells for energy and materials recycling: Redox mediators

This study disclosed why and how some decolorized intermediates (e.g., 2-aminophenol) could act as electron-shuttling mediator(s) to enhance the capabilities of reductive decolorization and bioelectricity generation. It also selected several model auxochrome-containing compounds structurally associated to 2AP to explore how chemical structure influenced the feasibility of possible electron shuttles for power producing capabilities in microbial fuel cells (MFCs). The selection criteria of electron-shuttling mediators were suggested for optimal reductive decolorization and bioelectricity generation in MFCs for practical application.     

Influence of electrode spacing and fed-batch operation on the maximum performance trend of a soil microbial fuel cell

The effect of electrode spacing on a soil microbial fuel cell (MFC) performance under fed-batch treatment with synthetic urine medium (SUM) was investigated at 2, 5, and 8 cm electrode spacing. The electrodes consisted of stainless-steel mesh with coarse layers of carbon-black. The MFCs were fed with SUM when the natural substrate of the medium was exhausted. Initial feeding resulted in 79.6, 108.7, and 103.1% increase in OCV with a proportional percentage increase in power at 2, 5, and 8 cm electrode spacing. Six days after the first feeding, the power was 189.9, 150.7, and 108. 5 mW/m² in ascending order of electrode spacing. With more extended treatment, the overall maximum power was obtained at 8 cm spacing. In ascending order of electrode spacing, the highest power (207.92, 263.38, and 271.1 mW/m²) was obtained on days 39, 42, and 93, respectively. The study shows that a larger anode-to-cathode distance requires a longer time for the soil MFC to achieve stable and maximum performance in fed-batch operation.     

Automatic control of load increases power and efficiency in a microbial fuel cell

Increasing power production and coulombic efficiency (CE) of microbial fuel cells (MFCs) is a common research ambition as the viability of the technology depends to some extent on these measures of performance. As MFCs are typically time varying systems, comparative studies of controlled and un-controlled external load impedance are needed to show if control affects the biocatalyst development and hence MFC performance. The application of logic based control of external load resistance is shown to increase the power generated by the MFC, when compared to an equivalent system which has a static resistive load. The controlled MFC generated 1600 ± 400 C, compared to 300 ± 10 C with an otherwise replicate fixed load MFC system. The use of a parsimonious gradient based control was able to increase the CE to within the range of 15.1-22.7%, while the CE for a 200 Ω statically loaded MFC lay in the range 3.3-3.7%. The controlled MFC improves the electrogenic anodic biofilm selection for power production, indicating that greater power and substrate conversion can be achieved by controlling load impedance. Load control ensured sustainable current demand, applied microbial selection pressures and provided near-optimal impedance for power transference, compared to the un-controlled system.     

Bioelectricity production from municipal leachate in a microbial fuel cell: Effect of two cathodic catalysts

The objective of this work was to evaluate the effect of the cathodic catalyst (either chalcogenide or Pt) on bioelectricity production from actual municipal leachate in a microbial fuel cell equipped with an anode made of granular graphite (MFC-G) and seeded with an inoculum enriched in Mn(IV)-reducing bacteria.     

A review of recent progress in coatings, surface modifications and alloy developments for solid oxide fuel cell ferritic stainless steel interconnects

Ferritic stainless steels have become the standard material for solid oxide fuel cell (SOFC) interconnect applications. The use of commercially available ferritic stainless steels, not specifically designed for interconnect application, however, presents serious issues leading to premature degradation of the fuel cell stack, particularly on the cathode side. These problems include rapidly increasing contact resistance and volatilization of Cr from the oxide scales, resulting in cathode chromium poisoning and cell malfunction. To overcome these issues, a variety of conductive/protective coatings, surface treatments and modifications as well as alloy development have been suggested and studied over the past several years. This paper critically reviews the attempts performed thus far to mitigate the issues associated with the use of ferritic stainless steels on the cathode side. Different approaches are categorized and summarized and examples for each case are provided. Finally, directions and recommendations for the future studies are presented.     

Acclimatization of a microbial consortium into a stable biofilm to produce energy and 1,3-propanediol from glycerol in a microbial fuel cell

Glycerol, a by-product of biodiesel production, is a potential substrate for producing electricity and value-added products in bioelectrochemical systems. Here, we demonstrate a strategy to establish a highly specific energy-producing biofilm from glycerol in a microbial fuel cell (MFC). The MFC fed with 1 g L^?1 glycerol achieved maximum voltage, power density, and current of 0.4 V, 152 mW m^?2, and 19.0 mA m^?2, respectively, operating at a resistance of 1000 Ω. These values were much higher than the values previously described for the same glycerol concentration. High-throughput sequencing demonstrated that substituting acetate for glycerol diminished the anodic microbial diversity. In addition, glycerol shifted the microbial community composition from electroactive bacteria genera such as Delftia, Advenella, Thauera, Stenotrophomonas, and Dysgonomonas to bacteria with dual functions of electricity generation and 1,3-propanediol formation, including Citrobacter, Pseudomonas, and Klebsiella. Thus, establishing this biofilm opens the possibility of recovering energy and obtaining an added-value product from glycerol.     

Novel multi walled carbon nanotube based nitrogen impregnated Co and Fe cathode catalysts for improved microbial fuel cell performance

For application in a microbial fuel cell (MFC), transition metal and nitrogen co-doped nanocarbon catalysts were synthesised by pyrolysis of multi-walled carbon nanotubes (MWCNTs) in the presence of iron- or cobalt chloride and nitrogen source. For the physicochemical characterisation of the catalysts, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) was used. The results obtained by rotating disk electrode (RDE) method showed an extraordinary electrocatalytic activity of these catalysts towards oxygen reduction reaction (ORR) in neutral media, which was also confirmed by the MFC results. The Co-N-CNT and Fe-N-CNT cathode catalysts exhibited maximum power density of 5.1 W m^?3 and 6 W m^?3, respectively. Higher ORR activity and improved electric output in the MFC could be attributed to the formation of the active nitrogen-metal centers. All findings suggest that these materials can be used as potential cathode catalysts for ORR in MFC to replace expensive noble-metal based materials.     

Preparation and properties on the graphite/polypropylene composite bipolar plates with a 304 stainless steel by compression molding for PEM fuel cell

Graphite/polymer composites have high corrosion resistance, low contact resistance and low fabrication cost but low cell efficiency and mechanical strength. This study examined the electrical and mechanical properties of graphite/polypropylene composite bipolar plates. Carbon nanotubes (CNTs) were used to improve the electrical properties of the graphite/PP composites. Although the electrical properties increased when excess conducting filler was added to the composite, the mechanical strength decreased significantly. 304 stainless steel (304 SS) plates with different thicknesses were used as the support material of a graphite/PP composite bipolar plate. The 304 SS-supported graphite/PP composite bipolar plate had an optimum CNTs/graphite/PP composite composition of 1.2, 83 and 17 wt.%, respectively. The flexural strength of the 304 SS-supported graphite/PP composites increased from 35 to 58 MPa with increasing 304 SS thickness from 0.5 to 1 mm. The power density of the graphite bipolar plate and 304 SS-supported graphite/PP composite bipolar plate were 968 and 877 mW cm⁻², respectively. The 304 SS complemented the mechanical strength of the graphite/PP composite bipolar plate as well as the cell efficiency.