polymer fuel cells
TRANSCRIPT
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Onashan Pillay 207500797
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What is a fuel cell?
Electrochemical cell, exploiting chemical
reaction to produce electrical energy
Fuel is hydrogen and oxygen, in this
case
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Types of fuel cells
Polymer electrolyte membrane or proton
exchange membrane (PEM)
Solid oxide (SOFC)
Molten carbonate (MCFC)
Direct-methanol fuel cell (DMFC)
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How does it work?
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Cell Details
H2 dissociates under presence of Ptcatalyst
Operates between 50C 120C
50% - 70% efficiency
Membrane does not allow H2 and O2 topass
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Cell Details
Pt nanoparticles coated onto carbon paper
(catalyst)
Pt coated side of catalyst faces membrane
Polymer electrolyte looks like cling wrap
Cells generate about 0.7 volts but can be
combined to achieve desired output
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Ionomer
Polymer is specifically an ionomer
Ionomers unique in that they are electrical
conducting polymers
Repeated units of electrically neutral unitsand portion of ionized units
Nafion, a specific type of ionomer, is mostpopular
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Nafion
Made from copolymerization of Teflonmonomer and alkyl vinyl ether withsulfonyl acid fluoride
Conducts cations extremely well
Mechanically and thermally stable
Extruded into thin films
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Relating to Coal Tech & Gas
Coal reserves are diminishing fast
Investigated as alternative to burning coal
Several advantages over coal burning
Can be compared to/measured against
current ways of generating electricity
H2 is from steam reforming mainly with HC
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Advantages
Low operating T; cell warms up quickand thus supplies electricity soon afterstartup
Low T means more reliability (High T inSOFC, cell breaks down)
DMFC less efficient, more expensivethan PEMFC
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Advantages
No emissions
No moving parts to decrease efficiency
Water is a byproduct
SAwill run out of coal eventually, eco-
friendly alternative
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Disadvantages
Stacked fuel cells use bipolar plates toconnect to each other
Metallic plates corrode, with byproductsdecreasing cell efficiency
Composites, light metals and graphiteplates can be used for low-temperatureFCs
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Disadvantages
SOFC & MCFC generates steam from
high T. Can be used in turbines
PEMFC are expensive (Pt catalyst,
bipolar plates)
Durability decreases with cycling
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Disadvantages
For membrane to function, water
management is crucial
Near upper limiting T, membrane loses
water and cannot take in cations
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Applications
Can be used as power source almost
anywhere
Transport is the major research area
since PEMFC cleaner, compact
Conventional cars known to have
efficiencies from 20%- 40%
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Applications
PEMFC alone has 50% - 70% efficiency
But considerH
2 must be produced atsome efficiency at some plant
Efficiency decreases sharply to below
48%
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Applications
PEMFC needs continuous flow of fuel
How practical & safe is this in a vehicle?
Onboard storage ofH2 being
investigated
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References
Nice, Karim, and Jonathan Strickland. "How Fuel CellsWork" 18 September 2000. HowStuffWorks.com. 13 March 2011
Amanda Meyer, Reaction Engineering of PolymerElectrolyte Membrane Fuel Cells, 25August 2004
http://en.wikipedia.org/wiki/
Elizabeth S.H
oward, The Design of Optimal MaterialCombinations for the Membrane ElectrodeAssembly of aProton Exchange Membrane Fuel Cell, May 2006,Princeton