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The Possibilities of Biological Fuel Cells

The Possibilities of Biological Fuel Cells. O 2. NO 3 -. Fe 3+. SO 4 2-. CO 2. CO 2. e -. H 2 O. N 2. Fe 2+. HS -. CH 4. Organic Carbon. Anode. Microbial Electricity Generation. CH 3 COO - + 2OH -  2CO 2 + 5H + + 8e -.

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The Possibilities of Biological Fuel Cells

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  1. The Possibilities of Biological Fuel Cells

  2. O2 NO3- Fe3+ SO42- CO2 CO2 e- H2O N2 Fe2+ HS- CH4 Organic Carbon Anode Microbial Electricity Generation CH3COO- + 2OH- 2CO2 + 5H+ + 8e- Microbial fuel cells are based on the recently identified ability of microorganisms to pass electrons directly onto the surfaces of electrodes during catabolic respiration.

  3. Two-chambered (poised-potential) electrochemical cell Reference electrode H2O Anaerobic Gr Gr Ag O2 + H+ + e- Graphite working electrode: Anode (oxidizing) Graphite counter electrode: Cathode (reducing) Cation-selective membrane

  4. Concept Organic carbon CO2 ESred CO2 ESox Organic carbon Microorganisms catabolize organic electron donors producing electrons which are transferred onto the anode Direct reduction Graphite Ag Indirect reduction

  5. Advantages of Biofuel cells • More efficient than turbine (~25%) or solar (~15%) electricity generation • Does not require substrate to be combustible • Does not require the use of toxic and expensive heavy metals or metalloids • Is not limited by the reactivity of the electron donor • Do not produce toxic endproducts

  6. Potential Applications of Biofuel cells • Powering Monitoring Devices in Remote Locations • Powering Electronic Devices from Renewable Energy Sources • Decentralized domestic power source • Conversion of waste organic matter to electricity instead of methane • Conversion of renewable biomass to electricity instead of ethanol • Bioremediation of environmental contaminants Improved efficiency

  7. Crucial parameters of operational effectiveness • Bacterial metabolism • Bacterial electron transfer • Performance of the cation selective membrane • Intrinsic electrical resistance of the system • Efficiency of the cathode oxidation step Biological Physical Chemical and Biological

  8. Studies done to date have: • Investigated electricity generation under constant resistance (load) or constant voltage • Investigated electricity generation by pure cultures under a poised potential with glucose, lactate, benzoate, acetate, or H2 as the electron donor • Investigated microbial communities on the anode surfaces in sediment systems with either glucose or NOM as the electron donor

  9. Redox E’o (mV) 2H+ + 2e- H2 -420 Ferredoxin(Fe3+) + e-  Ferredoxin(Fe2+) -420 NAD+ + H+ + 2e-  NADH -320 S + 2H+ + 2e-  H2S -274 SO42- + 10H+ + 8e-  H2S + 4H2O -220 Pyruvate2- + 2H+ + 2e-  lactate2- -185 FAD + 2H+ + 2e-  FADH2 -180 Fumarate2- + 2H+ + 2e-  Succinate2- +31 Cytochrome b(Fe3+) + e-  Cytochrome b(Fe2+) +75 Ubiquinone + 2H+ + 2e-  Ubiquinonered +100 Cytochrome c(Fe3+) + e-  Cytochrome c(Fe2+) +254 NO3- + 2H+ + 2e-  NO2- + H2O +421 NO2- + 8H+ + 6e-  NH4+ + 2H2O +440 O2 + 4H+ + 4e-  2H2O +840

  10. Anodic chamber Cathodic chamber H2 0.5 O2 2e- 2e- 2H+ H2O 2H+ 2H+ 1 2 3 4 5 6 7 +840 mV Over potentials/inefficiencies are associated with several different steps involved in the biological fuel cell -320 -420

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