Graphite anode surface modification with controlled reduction of specific aryl diazonium salts for improved microbial fuel cells power output

Graphite electrodes were modified with reduction of aryl diazonium salts and implemented as anodes in microbial fuel cells. First, reduction of 4-aminophenyl diazonium is considered using increased coulombic charge density from 16.5 to 200 mC/cm(2). This procedure introduced aryl amine functionalities at the surface which are neutral at neutral pH. These electrodes were implemented as anodes in "H" type microbial fuel cells inoculated with waste water, acetate as the substrate and using ferricyanide reduction at the cathode and a 1000 Ω external resistance. When the microbial anode had developed, the performances of the microbial fuel cells were measured under acetate saturation conditions and compared with those of control microbial fuel cells having an unmodified graphite anode. We found that the maximum power density of microbial fuel cell first increased as a function of the extent of modification, reaching an optimum after which it decreased for higher degree of surface modification, becoming even less performing than the control microbial fuel cell. Then, the effect of the introduction of charged groups at the surface was investigated at a low degree of surface modification. It was found that negatively charged groups at the surface (carboxylate) decreased microbial fuel cell power output while the introduction of positively charged groups doubled the power output. Scanning electron microscopy revealed that the microbial anode modified with positively charged groups was covered by a dense and homogeneous biofilm. Fluorescence in situ hybridization analyses showed that this biofilm consisted to a large extent of bacteria from the known electroactive Geobacter genus. In summary, the extent of modification of the anode was found to be critical for the microbial fuel cell performance. The nature of the chemical group introduced at the electrode surface was also found to significantly affect the performance of the microbial fuel cells. The method used for modification is easy to control and can be optimized and implemented for many carbon materials currently used in microbial fuel cells and other bioelectrochemical systems.     

Microbial fuel cell characterisation and evaluation of <Emphasis Type="Italic">Lysinibacillus macroides</Emphasis> MFC02 electrigenic capability

Microbial fuel cell (MFC) is the most prominent research field due to its capability to generate electricity by utilizing the renewable sources. In the present study, Two MFC designs namely, H type-Microbial fuel cell (HT-MFC) and U type-Microbial fuel cell (UT-MFC) were constructed based on standardized H shaped anode and cathode compartment as well as U shaped anode and cathode compartments, respectively. In order to lower the cost for MFC construction, Pencil graphite lead was used as electrode and salt agar as Proton exchange membrane. Results inferred that newly constructed UT-MFC showed high electron production when compared to the HT-MFC. UT-MFC displayed an output of about 377?±?18.85 mV (millivolts); whereas HT-MFC rendered only 237?±?11.85 mV (millivolts) of power generation, which might be due to the low internal resistance. By increasing the number of cathode in UT-MFC, power production was increased upto 313?±?15.65 mV in Open circuit voltage (OCV). Electrogenic bacteria namely, Lysinibacillus macroides (Acc. No. KX011879) rendered enriched power generation. The attachment of bacteria as a biofilm on pencil graphite lead was analyzed using fluorescent microscope and Scanning Electron Microscope (SEM). Based on our findings, it was observed that UT-MFC has a tendency to produce high electron generation using pencil graphite lead as the electrode material.     

Bioanode for a microbial fuel cell based on Gluconobacter oxydans immobilized into a polymer matrix

Acetic acid bacteria Gluconobacter oxydans subsp. industrius RKM V-1280 were immobilized into a synthetic matrix based on polyvinyl alcohol modified with N-vinylpyrrolidone and used as biocatalysts for the development of bioanodes for microbial fuel cells. The immobilization method did not significantly affect bacterial substrate specificity. Bioanodes based on immobilized bacteria functioned stably for 7 days. The maximum voltage (fuel cell signal) was reached when 100–130 μM of an electron transport mediator, 2,6-dichlorophenolindophenol, was added into the anode compartment. The fuel cell signals reached a maximum at a glucose concentration higher than 6 mM. The power output of the laboratory model of a fuel cell based on the developed bioanode reached 7 mW/m² with the use of fermentation industry wastes as fuel.     

Lack of electricity production by Pelobacter carbinolicus indicates that the capacity for Fe(III) oxide reduction does not necessarily confer electron transfer ability to fuel cell anodes

The ability of Pelobacter carbinolicus to oxidize electron donors with electron transfer to the anodes of microbial fuel cells was evaluated because microorganisms closely related to Pelobacter species are generally abundant on the anodes of microbial fuel cells harvesting electricity from aquatic sediments. P. carbinolicus could not produce current in a microbial fuel cell with electron donors which support Fe(III) oxide reduction by this organism. Current was produced using a coculture of P. carbinolicus and Geobacter sulfurreducens with ethanol as the fuel. Ethanol consumption was associated with the transitory accumulation of acetate and hydrogen. G. sulfurreducens alone could not metabolize ethanol, suggesting that P. carbinolicus grew in the fuel cell by converting ethanol to hydrogen and acetate, which G. sulfurreducens oxidized with electron transfer to the anode. Up to 83% of the electrons available in ethanol were recovered as electricity and in the metabolic intermediate acetate. Hydrogen consumption by G. sulfurreducens was important for ethanol metabolism by P. carbinolicus. Confocal microscopy and analysis of 16S rRNA genes revealed that half of the cells growing on the anode surface were P. carbinolicus, but there was a nearly equal number of planktonic cells of P. carbinolicus. In contrast, G. sulfurreducens was primarily attached to the anode. P. carbinolicus represents the first Fe(III) oxide-reducing microorganism found to be unable to produce current in a microbial fuel cell, providing the first suggestion that the mechanisms for extracellular electron transfer to Fe(III) oxides and fuel cell anodes may be different.     

Power output and columbic efficiencies from biofilms of Geobacter sulfurreducens comparable to mixed community microbial fuel cells

It has been previously noted that mixed communities typically produce more power in microbial fuel cells than pure cultures. If true, this has important implications for the design of microbial fuel cells and for studying the process of electron transfer on anode biofilms. To further evaluate this, Geobacter sulfurreducens was grown with acetate as fuel in a continuous flow 'ministack' system in which the carbon cloth anode and cathode were positioned in close proximity, and the cation-selective membrane surface area was maximized in order to overcome some of the electrochemical limitations that were inherent in fuel cells previously employed for the study of pure cultures. Reducing the size of the anode in order to eliminate cathode limitation resulted in maximum current and power densities per m(2) of anode surface of 4.56 A m(-2) and 1.88 W m(-2) respectively. Electron recovery as current from acetate oxidation was c. 100% when oxygen diffusion into the system was minimized. This performance is comparable to the highest levels previously reported for mixed communities in similar microbial fuel cells and slightly higher than the power output of an anaerobic sludge inoculum in the same ministack system. Minimizing the volume of the anode chamber yielded a volumetric power density of 2.15 kW m(-3), which is the highest power density per volume yet reported for a microbial fuel cell. Geobacter sulfurreducens formed relatively uniform biofilms 3-18 mum thick on the carbon cloth anodes. When graphite sticks served as the anode, the current density (3.10 A m(-2)) was somewhat less than with the carbon cloth anodes, but the biofilms were thicker (c. 50 mum) with a more complex pillar and channel structure. These results suggest that the previously observed disparity in power production in pure and mixed culture microbial fuel cell systems can be attributed more to differences in the fuel cell designs than to any inherent superior capability of mixed cultures to produce more power than pure cultures.     

Improved fuel cell and electrode designs for producing electricity from microbial degradation

A new one-compartment fuel cell was composed of a rubber bunged bottle with a center-inserted anode and a window-mounted cathode containing an internal, proton-permeable porcelain layer. This fuel cell design was less expensive and more practical than the conventional two-compartment system, which requires aeration and a ferricyanide solution in the cathode compartment. Three new electrodes containing bound electron mediators including a Mn(4+)-graphite anode, a neutral red (NR) covalently linked woven graphite anode, and an Fe(3+)-graphite cathode were developed that greatly enhanced electrical energy production (i.e., microbial electron transfer) over conventional graphite electrodes. The potentials of these electrodes measured by cyclic voltametry at pH 7.0 were (in volts): +0.493 (Fe(3+)-graphite); +0.15 (Mn(4+)-graphite); and -0.53 (NR-woven graphite). The maximal electrical productivities obtained with sewage sludge as the biocatalyst and using a Mn(4+)-graphite anode and a Fe(3+)-graphite cathode were 14 mA current, 0.45 V potential, 1,750 mA/m(2) current density, and 788 mW/m(2) of power density. With Escherichia coli as the biocatalyst and using a Mn(4+)-graphite anode and a Fe(3+)-graphite cathode, the maximal electrical productivities obtained were 2.6 mA current, 0.28 V potential, 325 mA/m(2) current density, and 91 mW/m(2) of power density. These results show that the amount of electrical energy produced by microbial fuel cells can be increased 1,000-fold by incorporating electron mediators into graphite electrodes. These results also imply that sewage sludge may contain unique electrophilic microbes that transfer electrons more readily than E. coli and that microbial fuel cells using the new Mn(4+)-graphite anode and Fe(3+)-graphite cathode may have commercial utility for producing low amounts of electrical power needed in remote locations.     

Use of an oxygen gas diffusion cathode and a three-dimensional packed bed anode in a bioelectrochemical fuel cell

Summary An oxygen gas diffusion electrode was successfully used as a cathode in a bioelectro-chemical fuel cell with 2-hydroxy-1,4-naphthoquinone as redox-mediator and Escherichia coli as biocatalyst. On addition of bacteria to the anode compartment of the fuel cell a rapid increase in the electricity output was observed. With the use of a three-dimensional packed bed anode the electricity output of the cell could be considerably increased.     

Understanding the Anodic Mechanism of a Seafloor Fuel Cell: Interactions Between Geochemistry and Microbial Activity

Seafloor fuel cells made with graphite electrodes generate electricity by promoting electron transfer in response to a natural voltage difference (−0.7 to −0.8 V) between anoxic sediments and overlying oxic seawater. Geochemical impacts of a seafloor fuel cell on sediment solids and porewaters were examined to identify the anodic mechanisms and substrates available for current production. In an estuarine environment with little dissolved sulfide, solid-phase acid volatile sulfide and Cr²⁺-reducible sulfur minerals decreased significantly toward the anode after 7 months of nearly continuous energy harvesting. Porewater iron and sulfate increased by millimolar amounts. Scanning electron microscope images showed a biofilm overcoating the anode, and electron microprobe analyses revealed accumulations of sulfur, iron, silicon and phosphorus at the electrode surface. Sulfur deposition was also observed on a laboratory fuel cell anode used to generate electricity with only dissolved sulfide as an electron donor. Moreover, current densities and voltages displayed by these purely chemical cells were similar to the values measured with field devices. These results indicate that electron transfer to seafloor fuel cells can readily result in the oxidation of dissolved and solid-phase forms of reduced sulfur producing mainly S⁰ which deposits at the electrode surface. This oxidation product is consistent with the observed enrichment of bacteria most closely related to Desulfobulbus/Desulfocapsa genera within the anode biofilm, and its presence is proposed to promote a localized biogeochemical cycle whereby biofilm bacteria regenerate sulfate and sulfide. This electron-shuttling mechanism may co-occur while these or other bacteria use the anode directly as a terminal electron acceptor.     

Construction and operation of freshwater sediment microbial fuel cell for electricity generation

In this work, sediment microbial fuel cell (SMFC) with granule activated carbon (GAC) cathode and stainless steel anode was constructed in laboratory tests and various factors on SMFC power output were investigated. The maximum power densities for the SMFC with GAC cathode was 3.5 mW m⁻², it was much higher than SMFC with round stainless steel cathode. Addition of cellulose reduced the output power from SMFC at the beginning of experiments, while the output power was found to increase after adding cellulose to sediments on day 90 of operation. On 160 day, maximum power density from the SMFC with adding 0.2% cellulose reached to 11.2 mW m⁻². In addition, the surface morphology of stainless steel anode on day 90 was analyzed by scanning electron microscope. It was found that the protection layer of the stainless steel as electrode in SMFCs was destroyed to some extent.     

A mediated glucose/oxygen enzymatic fuel cell based on printed carbon inks containing aldose dehydrogenase and laccase as anode and cathode

Enzyme electrodes show great potential for many applications, as biosensors and more recently as anodes and cathodes in biocatalytic fuel cells for power generation. Enzymes have advantages over metal catalysts, as they provide high specificity and reaction rates, while operating under mild conditions. Here we report on studies related to development of mass-producible, completely enzymatic printed glucose/oxygen biofuel cells. The cells are based on filter paper coated with conducting carbon inks containing mediators and laccase, for reduction of oxygen, or aldose dehydrogenase, for oxidation of glucose. Mediator performance in these printed formats is compared to relative rate constants for the enzyme-mediator reaction in solution, for a range of anode and cathode mediators. The power output and stability of fuels cells using an acidophilic laccase isolated from Trametes hirsuta is greater, at pH 5, than that for cells based on Melanocarpus albomyces laccase, that shows optimal activity closer to neutral pH, at pH 6. Highest power output, although of limited stability, was observed for ThL/ABTS cathodes, providing a maximum power density of 3.5 μWcm(-2) at 0.34 V, when coupled to an ALDH glucose anode mediated by an osmium complex. The stability of cell voltage above a threshold of 200 mV under a moderate 75 kΩ load is used to benchmark printed fuel cell performance. Highest stability was obtained for a printed fuel cell using osmium complexes as mediators of glucose oxidation by aldose dehydrogenase, and oxygen reduction by T. hirsuta laccase, maintaining cell voltage above 200 mV for 137 h at pH 5. These results provide promising directions for further development of mass-producible, completely enzymatic, printed biofuel cells.     

Selection of a variant of Geobacter sulfurreducens with enhanced capacity for current production in microbial fuel cells

Geobacter sulfurreducens produces current densities in microbial fuel cells that are among the highest known for pure cultures. The possibility of adapting this organism to produce even higher current densities was evaluated. A system in which a graphite anode was poised at −400 mV (versus Ag/AgCl) was inoculated with the wild-type strain of G. sulfurreducens, strain DL-1. An isolate, designated strain KN400, was recovered from the biofilm after 5 months of growth on the electrode. KN400 was much more effective in current production than strain DL-1. This was apparent with anodes poised at −400 mV, as well as in systems run in true fuel cell mode. KN400 had current (7.6 A/m²) and power (3.9 W/m²) densities that respectively were substantially higher than those of DL1 (1.4 A/m² and 0.5 W/m²). On a per cell basis KN400 was more effective in current production than DL1, requiring thinner biofilms to make equivalent current. The enhanced capacity for current production in KN400 was associated with a greater abundance of electrically conductive microbial nanowires than DL1 and lower internal resistance (0.015 versus 0.130 Ω/m²) and mass transfer limitation in KN400 fuel cells. KN400 produced flagella, whereas DL1 does not. Surprisingly, KN400 had much less outer-surface c-type cytochromes than DL1. KN400 also had a greater propensity to form biofilms on glass or graphite than DL1, even when growing with the soluble electron acceptor, fumarate. These results demonstrate that it is possible to enhance the ability of microorganisms to electrochemically interact with electrodes with the appropriate selective pressure and that improved current production is associated with clear differences in the properties of the outer surface of the cell that may provide insights into the mechanisms for microbe–electrode interactions.     

Lack of Electricity Production by Pelobacter carbinolicus Indicates that the Capacity for Fe(III) Oxide Reduction Does Not Necessarily Confer Electron Transfer Ability to Fuel Cell Anodes

The ability of Pelobacter carbinolicus to oxidize electron donors with electron transfer to the anodes of microbial fuel cells was evaluated because microorganisms closely related to Pelobacter species are generally abundant on the anodes of microbial fuel cells harvesting electricity from aquatic sediments. P. carbinolicus could not produce current in a microbial fuel cell with electron donors which support Fe(III) oxide reduction by this organism. Current was produced using a coculture of P. carbinolicus and Geobacter sulfurreducens with ethanol as the fuel. Ethanol consumption was associated with the transitory accumulation of acetate and hydrogen. G. sulfurreducens alone could not metabolize ethanol, suggesting that P. carbinolicus grew in the fuel cell by converting ethanol to hydrogen and acetate, which G. sulfurreducens oxidized with electron transfer to the anode. Up to 83% of the electrons available in ethanol were recovered as electricity and in the metabolic intermediate acetate. Hydrogen consumption by G. sulfurreducens was important for ethanol metabolism by P. carbinolicus. Confocal microscopy and analysis of 16S rRNA genes revealed that half of the cells growing on the anode surface were P. carbinolicus, but there was a nearly equal number of planktonic cells of P. carbinolicus. In contrast, G. sulfurreducens was primarily attached to the anode. P. carbinolicus represents the first Fe(III) oxide-reducing microorganism found to be unable to produce current in a microbial fuel cell, providing the first suggestion that the mechanisms for extracellular electron transfer to Fe(III) oxides and fuel cell anodes may be different.     

Long-term performance of a plant microbial fuel cell with Spartina anglica

The plant microbial fuel cell is a sustainable and renewable way of electricity production. The plant is integrated in the anode of the microbial fuel cell which consists of a bed of graphite granules. In the anode, organic compounds deposited by plant roots are oxidized by electrochemically active bacteria. In this research, salt marsh species Spartina anglica generated current for up to 119 days in a plant microbial fuel cell. Maximum power production was 100 mW m⁻² geometric anode area, highest reported power output for a plant microbial fuel cell. Cathode overpotential was the main potential loss in the period of oxygen reduction due to slow oxygen reduction kinetics at the cathode. Ferricyanide reduction improved the kinetics at the cathode and increased current generation with a maximum of 254%. In the period of ferricyanide reduction, the main potential loss was transport loss. This research shows potential application of microbial fuel cell technology in salt marshes for bio-energy production with the plant microbial fuel cell.     

Growth with high planktonic biomass in Shewanella oneidensis fuel cells

Shewanella oneidensis MR-1 grew for over 50 days in microbial fuel cells, incompletely oxidizing lactate to acetate with high recovery of the electrons derived from this reaction as electricity. Electricity was produced with lactate or hydrogen and current was comparable to that of electricigens which completely oxidize organic substrates. However, unlike fuel cells with previously described electricigens, in which cells are primarily attached to the anode, at least as many of the S. oneidensis cells were planktonic as were attached to the anode. These results demonstrate that S. oneidensis may conserve energy for growth with an electrode serving as an electron acceptor and suggest that multiple strategies for electron transfer to fuel cell anodes exist.     

Enzymatic biofuel cell based on anode and cathode powered by ethanol

Enzymatic biofuel cell based on enzyme modified anode and cathode electrodes are both powered by ethanol and operate at ambient temperature is described. The anode of the presented biofuel cell was based on immobilized quino-hemoprotein-alcohol dehydrogenase (QH-ADH), while the cathode on co-immobilized alcohol oxidase (AOx) and microperoxidase (MP-8). Two enzymes AOx and MP-8 acted in the consecutive mode and were applied in the design of the biofuel cell cathode. The ability of QH-ADH to transfer electrons directly towards the carbon-based electrode and the ability of MP-8 to accept electrons directly from the same type of electrodes was exploited in this biofuel cell design. Direct electron transfer (DET) to/from enzymes was the basis for generating an electric potential between the anode and cathode. Application of immobilized enzymes and the harvesting of the same type of fuel at both electrodes (cathode and anode) avoided the compartmentization of enzymatic biofuel cell. The maximal open circuit potential of the biofuel cell was 240mV.     

Impact of electrode composition on electricity generation in a single-compartment fuel cell using Shewanella putrefaciens

The production of electricity by Shewanella putrefaciens in the absence of exogenous electron acceptors was examined in a single compartment fuel cell with different types of electrodes and varying physiological conditions. Electricity production was dependent on anode composition, electron donor type and cell concentration. A maximum current of 2.5 mA and a current density of 10.2 mW/m(2)electrode was obtained with a Mn(4+) graphite anode, 200 mM sodium lactate and a cell concentration of 3.9 g cell protein/ml. Current production by S. putrefaciens was enhanced 10-fold when an electron mediator (i.e., Mn(4+) or neutral red) was incorporated into the graphite anode.     

Microbial fuel cells: novel biotechnology for energy generation

Microbial fuel cells (MFCs) provide new opportunities for the sustainable production of energy from biodegradable, reduced compounds. MFCs function on different carbohydrates but also on complex substrates present in wastewaters. As yet there is limited information available about the energy metabolism and nature of the bacteria using the anode as electron acceptor; few electron transfer mechanisms have been established unequivocally. To optimize and develop energy production by MFCs fully this knowledge is essential. Depending on the operational parameters of the MFC, different metabolic pathways are used by the bacteria. This determines the selection and performance of specific organisms. Here we discuss how bacteria use an anode as an electron acceptor and to what extent they generate electrical output. The MFC technology is evaluated relative to current alternatives for energy generation.     

The effect of flavin electron shuttles in microbial fuel cells current production

The effect of electron shuttles on electron transfer to microbial fuel cell (MFC) anodes was studied in systems where direct contact with the anode was precluded. MFCs were inoculated with Shewanella cells, and flavins used as the electron shuttling compound. In MFCs with no added electron shuttles, flavin concentrations monitored in the MFCs' bulk liquid increased continuously with FMN as the predominant flavin. The maximum concentrations were 0.6 μM for flavin mononucleotide and 0.2 μM for riboflavin. In MFCs with added flavins, micro-molar concentrations were shown to increase current and power output. The peak current was at least four times higher in MFCs with high concentrations of flavins (4.5–5.5 μM) than in MFCs with low concentrations (0.2–0.6 μM). Although high power outputs (around 150 mW/m²) were achieved in MFCs with high concentrations of flavins, a Clostridium-like bacterium along with other reactor limitations affected overall coulombic efficiencies (CE) obtained, achieving a maximum CE of 13%. Electron shuttle compounds (flavins) permitted bacteria to utilise a remote electron acceptor (anode) that was not accessible to the cells allowing current production until the electron donor (lactate) was consumed.     

沉积型海底微生物燃料电池构建及其影响因素研究

海底微生物燃料电池具有底物丰富、可长期运行、维护成本低和环境友好等特点,具有很好的研究价值和广阔的发展前景。但由于其低的功率密度输出和长期运行的不稳定性,使海底微生物燃料电池尚未得到广泛地实际应用。选取海底沉积泥用于实验室构建的海底微生物燃料电池装置中,比较了在不同阳极材料、阴阳极面积比、阳极修饰、阳极泥下深度条件下海底微生物燃料电池的功率密度输出及其电化学性能,得出最佳的海底微生物燃料电池阳极材料为碳毡;阴极及电极最佳面积比为1∶1;最佳阳极修饰为氨水浸渍;最佳阳极泥下深度为2 cm。