fuel cells - university of mississippihome.olemiss.edu/~cmchengs/global warming/session 24...
TRANSCRIPT
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Fuel Cells
Amala DassDepartment of Chemistry & Biochemistry
1. Fuel cell basics1. Fuel cell basics
2. Fuel cell stacks – bipolar plates
3. Types of fuel cells
4. Proton Exchange Membrane fuel cells
5. Current status
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Cell voltage: connecting cells in series
Voltage of one fuel cell = 0.7 V
For useful voltage � collection of fuel cells needed � ‘stack’
-current collection issues � voltage drop
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BIPOLAR plate-Better method for cell interconnection
-makes connection all over one cathode and the anode of the next cell and also
Serves as a means of feeding O2 to cathode and fuel to the anode
-complex design; expensive to manufacture
-made from graphite
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Practical issues:
1. Slower reaction rate � low current & power
2. Availability of H2 as a fuel
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Types of Fuel Cells
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Proton Exchange Membrane(PEM) Fuel Cells
ion conduction polymer electrolyte (mobile ion = H+ ion or proton)
Anode-electrolyte-cathode ‘all-in-one’ assembly
� “membrance electrode assemblies”
Low temperature operation � can start quickly
Applications:
-cars, buses, combined heat and power systems
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How the polymer electrolyte works
Sulfonated fluoropolymers …. Nafion (Dupont)
Strong C-F bonds resists
chemical attacks
Polymer sulphonated with HSO3 to add an SO3- ion
Polymer – hydrophobic
SO3- � hydrophilic
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This leads to interesting hydrophilic/hydrophobic “micro-phase separated morphology”
�dilute acidic regions with a tough and strong hydrophobic structure
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Electrodes and electrode structure
Pt catalyst � cathode and anode
Few years ago, 28 mg per cm3 was used…
Today, 0.2 mg/cm2 is used (use of nanoparticles, etc)
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TEM image of fuel cell catalyst
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Fuelling fuel cells
H2 produced from
-Fossil fuels
-Petroleum
-Coal
-Bio-fuels
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Hydrogen storage
-compressed gas cylinders
-cryogenic liquids
-reversible metal hydride
-metal hydride reactions with water
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Safety issues – Hindenburg disaster
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BIPOLAR plate
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BIPOLAR plate
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