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Source: http://parts.mit.edu/igem07/images/2/2d/Fuelcell.JPG

Microbial Fuel Cells. Source: http://parts.mit.edu/igem07/images/2/2d/Fuelcell.JPG. Microbial Fuel Cells. anode. cathode. Source: http://parts.mit.edu/igem07/images/2/2d/Fuelcell.JPG. An anode and a cathode are connected by an external electrical circuit, .

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Source: http://parts.mit.edu/igem07/images/2/2d/Fuelcell.JPG

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  1. Microbial Fuel Cells Source: http://parts.mit.edu/igem07/images/2/2d/Fuelcell.JPG

  2. Microbial Fuel Cells anode cathode Source: http://parts.mit.edu/igem07/images/2/2d/Fuelcell.JPG

  3. An anode and a cathode are connected by an external electrical circuit, and separated internally by an ion exchange membrane.

  4. Microbes growing in the anodic chamber metabolize a carbon substrate (glucose in this case) to produce energy and hydrogen.

  5. C6H12O6 + 2H2O → 2CH3COOH + 2CO2 + 4H2 or C6H12O6 → CH3CH2CH2COOH + 2CO2 + 2H2 Hydrogen generated is reduced into hydrogen ions (proton) and electrons.

  6. Electrons are transferred to the anodic electrode, and then to the external electrical circuit. The protons move to the cathodic compartment via the ion exchange channel and complete the circuit.

  7. The electrons and protons liberated in the reaction recombine in the cathode. If oxygen is to be used as an oxidizing agent, water will be formed. An electrical current is formed from the potential difference of the anode and cathode, and power is generated.

  8. The anode and cathode electrodes are composed of graphite, carbon paper or carbon cloth. The anodic chamber is filled with the carbon substrate for the microbes to metabolize to grow and produce energy. The pH and buffering properties of the anodic chamber can be varied to maximize microbial growth, energy production, and electric potential.

  9. The anode and cathode electrodes are composed of graphite, carbon paper or carbon cloth. The cathodic chamber may be filled with air in which case oxygen is the oxidant.

  10. Laboratory substrates are acetate, glucose, or lactate. Real world substrates include wastewater and landfills. Substrate concentration, type, and feed rate can greatly affect the efficiency of a cell.

  11. Microbes should be anaerobic (fermentative type) because anodic chamber must be free of oxygen. Microbes tested are: E. coli Proteus vulgarisStreptococcus lactisStaphylococcus aureusPsuedomonas methanicaLactobacillus plantarium (Many of these species are known human pathogens, and pose a potential safety hazard.)

  12. Microbes should be anaerobic (fermentative type) because anodic chamber must be free of oxygen. Some bacteria, like Clostridium cellulolyticum, are able to use cellulose as a substrate to produce an electrical output between 14.3-59.2 mW/m2, depending on the type of cellulose.

  13. Proton Exchange Membrane (PEM) The PEM acts as the barrier between the anodic and cathodic chambers. It is commonly made from polymers like Nafion and Ultrex. Ideally, no oxygen should be able to circulate between the oxidizing environment of the cathode and the reducing environment of the anode. The detrimental effects of oxygen in the anode can be lessened by adding oxygen-scavenging species like cysteine.

  14. Real-life MFC

  15. Real-life MFC The MFC shown in this tabletop setup can take common sources of organic waste such as human sewage, animal waste, or agricultural runoff and convert them into electricity (Biodesign Institute).

  16. Real-life MFC Fuel cells like this are now used by a leading UK brewery to test the activity of the yeast used for their ales.

  17. Real-life MFC The black boxes arranged in a ring of the robot are MFCs, each generating a few microwatts of power, enough to fuel a simple brain and light-seeking behaviour in EcoBot-II.

  18. (http://microbialfuelcell.org).

  19. Conventional Fuel Cells Hydrogen is the fuel for Proton Exchange Membrane (PEM) fuel cells. At the anode, a platinum catalyst causes the hydrogen to split into positive hydrogen ions (protons) and negatively charged electrons.

  20. Conventional Fuel Cells The Proton Exchange Membrane (PEM) allows only the positively charged hydrogen ions (protons) to pass through it to the cathode. The negatively charged electrons must travel along an external circuit to the cathode, creating an electrical current.

  21. Conventional Fuel Cells At the cathode, the electrons and positively charged hydrogen ions combine with oxygen to form water, which flows out of the cell.

  22. Conventional Fuel Cells • Power is produced by an electrochemical process not by combustion • Noiseless operation • 50% hydrogen energy content to electrical energy conversion efficiency • Multi-fuel (hydrocarbon and alcohols) capability • Durability, reliability, scalability and ease of maintenance  • Only water and heat is emitted from a fuel cell (water is in fact a greenhouse gas)

  23. Conventional Fuel Cells • The electrodes are composed of platinum particles uniformly supported on carbon particles. The platinum acts as a catalyst. • Polymer Electrolyte Membrane (Proton Exchange Membrane) is a thin, solid, organic compound. • Hydrogen for the fuel cell is produced from fossil fuel at present (so CO2 emissions are part of hydrogen energy). • Power-plant-to-wheel efficiency of 22% if the hydrogen is stored as high-pressure gas, and 17% if it is stored as liquid hydrogen • Hydrogen transportation and refuelling

  24. Conventional Fuel Cells

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