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R. Shanthini 26 Feb 2010 Source: http://parts.mit.edu/igem07/images/2/2d/Fuelce Microbial Fuel Cells
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R. Shanthini 26 Feb 2010 Source: http://parts.mit.edu/igem07/images/2/2d/Fuelcell.JPG
Microbial Fuel Cells
R. Shanthini 26 Feb 2010
anode
cathode
Microbial Fuel Cells
Source: http://parts.mit.edu/igem07/images/2/2d/Fuelcell.JPG
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.
R. Shanthini 26 Feb 2010
Microbes growing in the anodic chamber metabolize a carbon substrate (glucose in this case) to produce energy and hydrogen.
R. Shanthini 26 Feb 2010
Hydrogen generated is reduced into hydrogen ions (proton) and electrons.
C6H12O6 + 2H2O → 2CH3COOH + 2CO2 + 4H2 or
C6H12O6 → CH3CH2CH2COOH + 2CO2 + 2H2
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.
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.
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.
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.
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.
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.)
R. Shanthini 26 Feb 2010
Microbes should be anaerobic (fermentative type) because anodic chamber must be free of oxygen.
Some bacteria, likeClostridium 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.
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.
R. Shanthini 26 Feb 2010
Real-life MFC
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).
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.
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.
R. Shanthini 26 Feb 2010
(http://microbialfuelcell.org).
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.
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
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
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
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 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
Conventional Fuel Cells
R. Shanthini 26 Feb 2010
Technological status Proton 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
