Proton Exchange Membrane Fuel Cells PEMFC
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1 Proton Exchange Membrane Fuel Cells PEMFC Jens Oluf Jensen Summer School on Materials for the Hydrogen Society, Reykjavik, June 19.-23. in 2008 Energy and Materials Science Group, Department of Chemistry, Technical University of Denmark, Kemitorvet 207, DK-2800 Kgs. Lyngby, Denmark Extraction of the energy H 2 → 2H + + 2e - (½O 2 + 2e - → O 2- ) ½O 2 + 2H + + 2e - → H 2 O H + → Electrolyte Electrode Negative electrode Anode (oxidation) Positive electrode Cathode (reduction) Electrode Anode (H 2 , negative) Proton conducting membrane Cathode (O 2 , positive) Building up a MEA MEA = Membrane Electrode Assembly Polymer fuel cell (PEMFC) Cathode: Pt on carbon ½O 2 + 2H + + 2e - → H 2 O Electrolyte: H + conducting polymer Perfluorosulphonic acid (e.g Nafion) Anode: Pt on carbon H 2 → 2H + 2e -
Transcript of Proton Exchange Membrane Fuel Cells PEMFC
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Proton Exchange Membrane Fuel Cells
PEMFC
Jens Oluf Jensen
Summer School on Materials for the Hydrogen Society, Reykjavik, June 19.-23. in 2008
Energy and Materials Science Group, Department of Chemistry, Technical University of Denmark,Kemitorvet 207, DK-2800 Kgs. Lyngby, Denmark
Extraction of the energy
H2 → 2H+ + 2e-(½O2 + 2e- → O2-)
½O2 + 2H+ + 2e- → H2O
H+ →
Electrolyte
Elec
trode
Negative electrodeAnode
(oxidation)
Positive electrodeCathode
(reduction)
Elec
trode
Anode(H2, negative)
Proton conducting membrane
Cathode(O2, positive)
Building up a MEA
MEA = Membrane Electrode Assembly
Polymer fuel cell (PEMFC)
Cathode: Pt on carbon ½O2 + 2H+ + 2e-
→ H2O
Electrolyte: H+ conducting polymer Perfluorosulphonic acid (e.g Nafion)
Anode: Pt on carbon H2 → 2H+ 2e-
2
Single cell
ElectrolyteCatalyst layer
Channel plate
Diffusion layer
Electrode structure
Gas
ElectrolyteChannel plateRip
Electrode substrate Catalystlayer
Micro-porouslayer
Ions
Electrons,Heat
Gas diffusion layer (GDL)
An MEA Single cell
Electrolyte
Anode (-)Cathode (+
)
Cannel plate
Channel plate
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Stacking
+
-
Transport paths
Electrons and heat Reactants and products
Bipolarplate
Diffusion layer
Catalyst layerElectrolyte
Channel plates (bipolar plates)
Nexa from Ballard1200 W
Polymer fuel cell (PEMFC)
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Polymer fuel cell (PEMFC)
260 kW PEMFC with 205 kW motor, Ballard
GM/Opel Fuel Cell Marathon
http://www.gmeurope.com/marathon/
2004, 10 000 kmHydroGen3 (Opel Zafira)
Polymer fuel cell (PEMFC)
Reykjavik
Polymer fuel cell (PEMFC)
German submarine U - 212Siemens PEM fuel cellGfE metal hydride storage tank
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Polymer fuel cell (PEMFC)
2kWCHP
6kWCHP
From IRD Fuel Cells
Polymer fuel cell (PEMFC)
Advantages:• Compact construction• Large current density• Solid electrolyte• Low working temperature• Fast start-up
Disadvantages:• Water management• Noble metal catalyst• CO sensitive (must be < 20 ppm)• Cooling issues
Perfluorosulfonic acid polymers (Nafion®)
Nearly all PEMFC’sbased on
PFSA polymers(perfluorosulphonic acid)
Teflon
PFSA(Nafion)Developed
by DuPont
Proton conduction
Vehicle mechanismProton carried by water as H3O+, H5O2
+ etc
Grotthus mechanismProton jumping from H3O+ to H2O(Then another H+ can take the next jump)
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Water drag
Conductivity depends strongly on water content
H2
H2O
H7O3+ O2
Anode CathodeMembrane
e- e-H2O
Water management - a technical challengeToo little water => drying out, loss of conductivity
Too much water => condensation, flooding of electrodes
Cooling in cars
Water 60-70ºC 90-100ºCΔT(40 ºC) 20-30ºC 50-60ºC
Cooling a FC car requires a larger cooling system (radiator)
From DaimlerChrysler
How can a higher working temperature help ?
Advantages:• Higher CO tolerance• No water management• No liquid water• Higher value of excess heat• Easier cooling
Reformer / Reformer Brændselscelle / Fuel cell
ElNat. Gas,Methanol
H2CO2CO CO-oprensning
til 0,001 %
CO clean-upto 0,001 %
H2CO2
Varme/heat
Luft indAir in
Luft udAir out
Befugtning afluften
Humidificationof the air
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Luft indAir in
Luft udAir out
Befugtning afluften
Humidificationof the air
H2CO2
H2CO2CO CO-oprensning
til 0,001 %
CO clean-upto 0,001 %
Reformer / Reformer Brændselscelle / Fuel cell
ElNat. Gas,Methanol
Varme/heat
Other attempts
Replacement of sulphonic acid- Phosphonic acid- Other side chains- Other acceptor/donors
Replacement of water-H2SO4-H3PO4-CF3SO3H
Almindelige PEM-celler er baseretpå membraner som Nafion
Maksimal temperatur:ca. 80°C
Conventional PEMFC are basedon Membranes like Nafion
Maximum temperatureca. 80°C
NafionN
N
N
Nn
HH
Poly (2,2´-m-(phenylene)-5,5´-bibenzimidazole)
PBI
Nymembranaf PBI og
phosphorsyre
Maksimal temperatur:ca. 200°C
New membrane of PBI and phosphoricacid
Maximum temperature: ca. 200°C
Direct methanol fuel cell (DMFC)
(A special PEMFC)
Anode: CH3OH + H2O → 6H+ +6e- + CO2
Cathode: 1.5O2 + 6H+ + 6e- → 3H2O
Electrolyte: Ion conducting polymer (e.g. Nafion)Catalysts: Noble metals (Pt and Pt alloys)
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Direct methanol fuel cell (DMFC)
Size: < 1W - 1 kW
Applications:• Portable electronics (laptops, phones, MP3...)• Small/medium UPS systems• Remote power
DMFC
DMFC
DMFCIRD Fuel cells
DMFC
ToshibaDMFC for 1) a laptop2) an MP3 player
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DMFC DMFC
Direct methanol fuel cell (DMFC)
Advantages:• Liquid fuel• Easy and fast fuelling• Easy and compact fuel storage
Disadvantages:• Low efficiency• Fuel crossover• Expensive catalyst (10xPt amount)• MeOH poisonous
Example System (bus)
Motor etc. 14 kW
DC
/DC
13 kW
Cooler 20 kW
Com
pr47 kWFC
heat285 kW
Fuel545 kW
FC el.260 kW 213 kW 193 kW 180 kW
Work166 kW
30%
Losses:
Power
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Some of the problems
• Cost• Hydrogen storage in vehicles• Efficient hydrogen production• Durability of cells• Noble metals supply• Infrastructure• Numerous technical details
Polymer fuel cell (PEMFC)
From IRD Fuel cells
