electrochemistry : introduction, basic...
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FUEL CELLS
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Fuel cells
Introduction
Low temperature type
• PAFC (Phosphoric Acid Fuel Cell)
• AFC (Alkaline Fuel Cell)
• PEMFC (Polymer Electrolyte Membrane Fuel Cell)
• DMFC (Direct Methanol Fuel Cell)
High temperature type
• MCFC (Molten Carbonate Fuel Cell)
• SOFC (Solid Oxide Fuel Cell)
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Fuel cells: Introduction
1. Basic structure
2. Characteristic
3. Classification
Basic structure of fuel cells
: anode (H2) ǀ electrolyte ǀ cathode (O2)
: H2 (or H2-source) and O2 are supplied from outside
: reaction of water formation in basic
(H2+1/2O2 → H2O)
: stack structure to get high voltage
High efficiency / Environmentally friendly
: direct production of electric power
(thermal power generation: fossil fuel → heat→ mechanical energy (turbine) → electric energy)
: by-product (heat, hot water, steam) can be utilized
: No exhaust fume, No noise
Classification depending on
: working temperature (low temp./ high temp.)
: electrolyte (liquid / solid)
: fuel
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* 전기화학 (오승모 저)
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Low temperature type FC
1. PAFC (Phosphoric Acid Fuel Cell)
2. AFC (Alkaline Fuel Cell)
3. PEMFC (Polymer electrolyte Membrane Fuel Cell)
4. DMFC (Direct Methanol Fuel Cell)
PAFC
: phosphoric acid electrolyte
: H2 is applied by reforming hydrocarbons
H2 → 2H++2e-
1/2O2+2H++2e- → H2O
: H2+1/2O2 → H2O
cf) generation of hydrogen
: Electrolysis of water / reforming of hydrocarbons / Coal methods / etc.
AFC
: KOH aqueous solution electrolyte
H2+2OH- → 2H2O+2e-
1/2O2+H2O+2e- → 2OH-
: H2+1/2O2 → H2O
: CO2 forms KHCO3 degrading the performance
: high purity of H2 and O2 should be supplied
: special application (spacecraft)
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* 재료전기화학 (이철태 저)
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* 재료전기화학 (이철태 저)
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Low temperature type FC
1. PAFC (Phosphoric Acid Fuel Cell)
2. AFC (Alkaline Fuel Cell)
3. PEMFC (Polymer electrolyte Membrane Fuel Cell)
4. DMFC (Direct Methanol Fuel Cell)
PEMFC
: proton-exchange membrane electrolyte (Nafion)
H2 → 2H++2e-
1/2O2+2H++2e- → H2O
: H2+1/2O2 → H2O
: poisoning of Pt catalyst by CO at low temperatures
: polyimide, polyacryl are investigated for high temperature operation over 120oC
DMFC
: similar structure with PEMFC
: methanol is used as a hydrogen source
: small size, mobile application
CH3OH+H2O → CO2+6H++6e-
3/2O2+6H++6e- → 3H2O
: CH3OH+3/2O2 → CO2+2H2O
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* 전기화학 (오승모 저)
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High temperature type FC
1. MCFC (Molten Carbonate Fuel Cell)
2. SOFC (Solid Oxide Fuel Cell)
MCFC
: molten Li2CO3/K2CO3 electrolyte (over 600oC)
: reforming of hydrocarbon inside the cell owing to high operation temperature
2H2+2CO32- → 2CO2+2H2O+4e-
O2+2CO2+4e- → 2CO32-
: 2H2+O2 → 2H2O
: CO2 should be supplied to the cathode side
(recycle from the anode)
SOFC
: ion-conductive oxide electrolyte
(Yittria Stabilized Zirconia, YSZ, for O2- conduction)
(BaCe5.2Sm0.2O3-α for proton conduction)
H2+O2- → H2O+2e-
1/2O2+2e- → O2- (O2--conduction type)
H2 → 2H++2e-
2H++2e-+1/2O2 → H2O (H+-conduction type)
: high temperature operation (800~1000oC)
: technical difficulty of sealing, heat-expansion, etc.
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* 재료전기화학 (이철태 저)
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* 전기화학 (오승모 저)
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* 전기화학 (오승모 저)
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* 전기화학 (오승모 저)
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