Microbial Fuel Cells Methodology And Technology-Books Pdf

Microbial Fuel Cells Methodology and Technology
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and equipment indicating there is a need in the literature. for a paper that provides a more comprehensive source of. this information In this paper we therefore review existing. types of MFCs provide information on construction materials. and give examples of manufacturers although this should. not be considered an endorsement of a particular company. and describe methods of data analysis and reporting in order. to provide information to researchers interested in dupli. cating or advancing MFCs technologies Additional infor. mation is available on the microbial fuel cell website. www microbialfuelcell org, MFC Designs, Many different configurations are possible for MFCs Figures. 2 and 3 A widely used and inexpensive design is a two. chamber MFC built in a traditional H shape consisting. usually of two bottles connected by a tube containing a. separator which is usually a cation exchange membrane. CEM such as Nafion 12 13 23 27 or Ultrex 18 or a plain. salt bridge 27 Figure 2a f The key to this design is to. choose a membrane that allows protons to pass between the. FIGURE 1 Operating principles of a MFC not to scale A bacterium chambers the CEM is also called a proton exchange. in the anode compartment transfers electrons obtained from an membrane PEM but optimally not the substrate or electron. electron donor glucose to the anode electrode This occurs either acceptor in the cathode chamber typically oxygen In the. through direct contact nanowires or mobile electron shuttles small. H configuration the membrane is clamped in the middle of. spheres represent the final membrane associated shuttle During. the tubes connecting the bottle Figure 2f However the. electron production protons are also produced in excess These. protons migrate through the cation exchange membrane CEM into tube itself is not needed As long as the two chambers are. the cathode chamber The electrons flow from the anode through kept separated they can be pressed up onto either side of. an external resistance or load to the cathode where they react the membrane and clamped together to form a large surface. with the final electron acceptor oxygen and protons 26 Figure 2b An inexpensive way to join the bottles is to use. a glass tube that is heated and bent into a U shape filled. are reported with different reference states and sometimes with agar and salt to serve the same function as a cation. only under a single load resistor The range of conditions exchange membrane and inserted through the lid of each. and in some cases a lack of important data like the internal bottle Figure 2a The salt bridge MFC however produces. resistance or power densities derived from polarization curves little power due the high internal resistance observed. taken using different methods has made it difficult to H shape systems are acceptable for basic parameter. interpret and compare results among these systems 26 research such as examining power production using new. The variation in reported data has created a need to clarify materials or types of microbial communities that arise during. methods of data collection and reporting We have individu the degradation of specific compounds but they typically. ally received many requests from researchers for details on produce low power densities The amount of power that is. construction of MFCs and for names of providers of materials generated in these systems is affected by the surface area of. FIGURE 2 Types of MFCs used in studies A easily constructed system containing a salt bridge shown by arrow 27 B four batch type. MFCs where the chambers are separated by the membrane without a tube and held together by bolts 7 C same as B but with a. continuous flow through anode granular graphite matrix and close anode cathode placement 75 D photoheterotrophic type MFC 76. E single chamber air cathode system in a simple tube arrangement 30 F two chamber H type system showing anode and cathode. chambers equipped for gas sparging 23, 5182 9 ENVIRONMENTAL SCIENCE TECHNOLOGY VOL 40 NO 17 2006. FIGURE 3 MFCs used for continuous operation A upflow tubular type MFC with inner graphite bed anode and outer cathode 35 B. upflow tubular type MFC with anode below and cathode above the membrane is inclinated 36 C flat plate design where a channel. is cut in the blocks so that liquid can flow in a serpentine pattern across the electrode 17 D single chamber system with an inner. concentric air cathode surrounded by a chamber containing graphite rods as anode 34 E stacked MFC in which 6 separate MFCs are. joined in one reactor block 25, the cathode relative to that of the anode 28 and the surface coatings such as polytetrafloroethylene PTFE to the outside. of the membrane 29 The power density P produced by of the cathode that permit oxygen diffusion but limit bulk. these systems is typically limited by high internal resistance water loss 32. and electrode based losses see below When comparing Several variations on these basic designs have emerged. power produced by these systems it makes the most sense in an effort to increase power density or provide for. to compare them on the basis of equally sized anodes continuous flow through the anode chamber in contrast to. cathodes and membranes 29 the above systems which were all operated in batch mode. Using ferricyanide as the electron acceptor in the cathode Systems have been designed with an outer cylindrical reactor. chamber increases the power density due to the availability with a concentric inner tube that is the cathode 33 34 Figure. of a good electron acceptor at high concentrations Ferri 3d and with an inner cylindrical reactor anode consisting. cyanide increased power by 1 5 to 1 8 times compared to a of granular media with the cathode on the outside 35. Pt catalyst cathode and dissolved oxygen H design reactor Figure 3a Another variation is to design the system like an. with a Nafion CEM 29 The highest power densities so far upflow fixed bed biofilm reactor with the fluid flowing. reported for MFC systems have been low internal resistance continuously through porous anodes toward a membrane. systems with ferricyanide at the cathode 6 18 While separating the anode from the cathode chamber 36 Figure. ferricyanide is an excellent catholyte in terms of system 3b Systems have been designed to resemble hydrogen fuel. performance it must be chemically regenerated and its use cells where a CEM is sandwiched between the anode and. is not sustainable in practice Thus the use of ferricyanide cathode Figure 3c To increase the overall system voltage. is restricted to fundamental laboratory studies MFCs can be stacked with the systems shaped as a series of. It is not essential to place the cathode in water or in a flat plates or linked together in series 25 Figure 3e. separate chamber when using oxygen at the cathode The Sediment MFCs By placing one electrode into a marine. cathode can be placed in direct contact with air Figures 2e sediment rich in organic matter and sulfides and the other. 3c 3d either in the presence or absence of a membrane in the overlying oxic water electricity can be generated at. 30 In one system a kaolin clay based separator and graphite sufficient levels to power some marine devices 37 38. cathode were joined to form a combined separator cathode Protons conducted by the seawater can produce a power. structure 31 Much larger power densities have been density of up to 28 mW m2 Graphite disks can be used for. achieved using oxygen as the electron acceptor when the electrodes 12 37 although platinum mesh electrodes. aqueous cathodes are replaced with air cathodes In the have also been used 38 Bottle brush cathodes used for. simplest configuration the anode and cathode are placed seawater batteries may hold the most promise for long term. on either side of a tube with the anode sealed against a flat operation of unattended systems as these electrodes provide. plate and the cathode exposed to air on one side and water a high surface area and are made of noncorrosive materials. on the other Figure 2e When a membrane is used in this 39 Sediments have also been placed into H tube configured. air cathode system it serves primarily to keep water from two chamber systems to allow investigation of the bacterial. leaking through the cathode although it also reduces oxygen community 12. diffusion into the anode chamber The utilization of oxygen Modifications for Hydrogen Production By assisting. by bacteria in the anode chamber can result in a lower the potential generated by the bacteria at the anode with a. Coulombic efficiency defined as the fraction of electrons small potential by an external power source 0 25 V it is. recovered as current versus the maximum possible recovery possible to generate hydrogen at the cathode 40 43 These. see below 30 Hydrostatic pressure on the cathode will reactors called bioelectrochemically assisted microbial reac. make it leak water but that can be minimized by applying tors BEAMRs or biocatalyzed electrolysis systems are not. VOL 40 NO 17 2006 ENVIRONMENTAL SCIENCE TECHNOLOGY 9 5183. true fuel cells however as they are operated to produce Oxygen is the most suitable electron acceptor for an MFC. hydrogen not electricity Through modifications of the MFC due to its high oxidation potential availability low cost it. designs described above to contain a second chamber for is free sustainability and the lack of a chemical waste. capturing the hydrogen gas it should be possible to develop product water is formed as the only endproduct The choice. many new systems for hydrogen production of the cathode material greatly affects performance and is. varied based on application For sediment fuel cells plain. Materials of Construction graphite disk electrodes immersed in the seawater above the. sediment have been used 38 Due to the very slow kinetics. Anode Anodic materials must be conductive biocompatible. of the oxygen reduction at plain carbon and the resulting. and chemically stable in the reactor solution Metal anodes. large overpotential the use of such cathodes restricts the. consisting of noncorrosive stainless steel mesh can be utilized. use of this noncatalyzed material to systems that can tolerate. 44 but copper is not useful due to the toxicity of even trace. low performance In seawater oxygen reduction on carbon. copper ions to bacteria The most versatile electrode material. cathodes has been shown to be microbially supported 19. is carbon available as compact graphite plates rods or. 20 Such microbially assisted reduction has also been. granules as fibrous material felt cloth paper fibers foam. observed for stainless steel cathodes which rapidly reduces. and as glassy carbon There are numerous carbon suppliers. oxygen when aided by a bacterial biofilm 53, worldwide for example E TEK and Electrosynthesis Co Inc. To increase the rate of oxygen reduction Pt catalysts are. USA GEE Graphite Limited Dewsbury UK Morgan, usually used for dissolved oxygen 37 or open air gas.
Grimbergen Belgium and Alfa Aesar Germany, diffusion cathodes 34 48 To decrease the costs for the. The simplest materials for anode electrodes are graphite MFC the Pt load can be kept as low as 0 1 mg cm 2 54 The. plates or rods as they are relatively inexpensive easy to long term stability of Pt needs to be more fully investigated. handle and have a defined surface area Much larger surface and there remains a need for new types of inexpensive. areas are achieved with graphite felt electrodes 13 45 which catalysts Recently noble metal free catalysts that use. can have high surface areas 0 47 m2g 1 GF series GEE pyrolyzed iron II phthalocyanine or CoTMPP have been. Graphite limited Dewsbury UK However not all the proposed as MFC cathodes 54 55. indicated surface area will necessarily be available to bacteria Membrane The majority of MFC designs require the. Carbon fiber paper foam and cloth Toray have been separation of the anode and the cathode compartments by. extensively used as electrodes It has been shown that current a CEM Exceptions are naturally separated systems such as. increases with overall internal surface area in the order carbon sediment MFCs 37 or specially designed single compart. felt carbon foam graphite 46 Substantially higher ment MFCs 30 32 The most commonly used CEM is Nafion. surface areas are achieved either by using a compact material Dupont Co USA which is available from numerous. like reticulated vitreous carbon RVC ERG Materials and suppliers e g Aldrich and Ion Power Inc Alternatives to. Aerospace Corp Oakland CA 36 47 which is available Nafion such as Ultrex CMI 7000 Membranes International. with different pore sizes or by using layers of packed carbon Incorp Glen Rock NJ also are well suited for MFC. granules Le Carbone Grimbergen Belgium or beads 35 applications 6 and are considerably more cost effective than. 48 In both cases maintaining high porosity is important to Nafion When a CEM is used in an MFC it is important to. prevent clogging The long term effect of biofilm growth or recognize that it may be permeable to chemicals such as. particles in the flow on any of the above surfaces has not oxygen ferricyanide other ions or organic matter used as. been adequately examined the substrate The market for ion exchange membranes is. To increase the anode performance different chemical constantly growing and more systematic studies are neces. and physical strategies have been followed Park et al 31 sary to evaluate the effect of the membrane on perfo. Microbial Fuel Cells analysis of system performance This makes it difficult for researchers to compare devices on an equivalent basis The construction and analysis of MFCs requires knowledge of different scientific and engineering fields ranging from microbiology and electrochemistry to materials and environmentalengineering DescribingMFCsystemstherefore involves an understanding of

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