1. R. Shanthini 26 Feb 2010 Source: http://parts.mit.edu/igem07/images/2/2d/Fuelcell.JPG Microbial Fuel Cells

2. R. Shanthini 26 Feb 2010 anode cathode Microbial Fuel Cells Source: http://parts.mit.edu/igem07/images/2/2d/Fuelcell.JPG

3. R. Shanthini 26 Feb 2010 An anode and a cathode are connected by an external electrical circuit, and separated internally by an ion exchange membrane.

4. R. Shanthini 26 Feb 2010 Microbes growing in the anodic chamber metabolize a carbon substrate (glucose in this case) to produce energy and hydrogen.

5. R. Shanthini 26 Feb 2010 Hydrogen generated is reduced into hydrogen ions (proton) and electrons. C 6 H 12 O 6 + 2H 2 O → 2CH 3 COOH + 2CO 2 + 4H 2 or C 6 H 12 O 6 → CH 3 CH 2 CH 2 COOH + 2CO 2 + 2H 2

6. R. Shanthini 26 Feb 2010 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. R. Shanthini 26 Feb 2010 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. R. Shanthini 26 Feb 2010 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. R. Shanthini 26 Feb 2010 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. R. Shanthini 26 Feb 2010 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. R. Shanthini 26 Feb 2010 Microbes should be anaerobic (fermentative type) because anodic chamber must be free of oxygen. Microbes tested are: E. coli Proteus vulgaris Streptococcus lactis Staphylococcus aureus Psuedomonas methanica Lactobacillus plantarium (Many of these species are known human pathogens, and pose a potential safety hazard.)

12. R. Shanthini 26 Feb 2010 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/m 2, depending on the type of cellulose.

13. R. Shanthini 26 Feb 2010 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. R. Shanthini 26 Feb 2010 Real-life MFC

15. R. Shanthini 26 Feb 2010 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. R. Shanthini 26 Feb 2010 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. R. Shanthini 26 Feb 2010 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. R. Shanthini 26 Feb 2010 (http://microbialfuelcell.org).http://microbialfuelcell.org

19. R. Shanthini 26 Feb 2010 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. R. Shanthini 26 Feb 2010 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. Conventional Fuel Cells

21. R. Shanthini 26 Feb 2010 At the cathode, the electrons and positively charged hydrogen ions combine with oxygen to form water, which flows out of the cell. Conventional Fuel Cells

22. R. Shanthini 26 Feb 2010  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) Conventional Fuel Cells

23. R. Shanthini 26 Feb 2010  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 CO 2 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 Conventional Fuel Cells

24. R. Shanthini 26 Feb 2010 Technological statusProton Exchange Membrane (PEM) Fuel Cells): commercial in niche markets Solid Oxide Fuel Cells (SOFC): market entering phase in niche markets; Possible adverse effects disposal of worn-out fuel cells Conventional Fuel Cells