Extraction of the energy
Proton Exchange Membrane Fuel Cells
PEMFC
H2 → 2H+ + 2eJens Oluf Jensen
Energy and Materials Science Group, Department of Chemistry, Technical University of Denmark,
Kemitorvet 207, DK-2800 Kgs. Lyngby, Denmark
Summer School on Materials for the Hydrogen Society, Reykjavik, June 19.-23. in 2008
Negative electrode
Anode
(oxidation)
Building up a MEA
Anode
(H2, negative)
(½O2 + 2e- → O2-)
½O2 + 2H+ + 2e→ H2O
Positive electrode
Cathode
(reduction)
Polymer fuel cell (PEMFC)
Cathode:
Proton conducting
membrane
H+ →
Electrode
Electrode
Electrolyte
Pt on carbon
½O2 + 2H+ + 2e- → H2O
Electrolyte: H+ conducting polymer
Perfluorosulphonic acid (e.g Nafion)
Cathode
(O2, positive)
Anode:
MEA = Membrane Electrode Assembly
Pt on carbon
H2 → 2H+ 2e-
1
Single cell
Channel plate
Diffusion layer
Catalyst layer
Electrolyte
Electrode structure
Channel plate
Rip
Electrode substrate
Microporous Catalyst
layer
layer
Electrolyte
Electrons,
Heat
Ions
Gas
Gas diffusion layer (GDL)
An MEA
Single cell
e
lat
lp
+)
ne
n
e(
a
Ch thod lyte
o
e
Ca
(-)
ctr
lat
Ele ode el p
An ann
C
2
Stacking
Transport paths
Electrons and heat
Reactants and products
Bipolar
plate
Diffusion layer
Catalyst layer
Electrolyte
+
Channel plates (bipolar plates)
Polymer fuel cell (PEMFC)
Nexa from Ballard
1200 W
3
Polymer fuel cell (PEMFC)
GM/Opel Fuel Cell Marathon
2004, 10 000 km
HydroGen3 (Opel Zafira)
260 kW PEMFC with 205 kW motor, Ballard
http://www.gmeurope.com/marathon/
Polymer fuel cell (PEMFC)
Polymer fuel cell (PEMFC)
Reykjavik
German submarine U - 212
Siemens PEM fuel cell
GfE metal hydride storage tank
4
Polymer fuel cell (PEMFC)
2kW
CHP
Polymer fuel cell (PEMFC)
Advantages:
• Compact construction
• Large current density
• Solid electrolyte
• Low working temperature
• Fast start-up
6kW
CHP
Disadvantages:
• Water management
• Noble metal catalyst
From
IRD Fuel Cells
• CO sensitive (must be < 20 ppm)
• Cooling issues
Perfluorosulfonic acid polymers (Nafion®)
Nearly all PEMFC’s
based on
PFSA polymers
(perfluorosulphonic acid)
Teflon
Developed
by DuPont
Proton conduction
Vehicle mechanism
Proton carried by water as H3O+, H5O2+ etc
Grotthus mechanism
Proton jumping from H3O+ to H2O
(Then another H+ can take the next jump)
PFSA
(Nafion)
5
Water drag
Cooling in cars
Anode Membrane Cathode
e-
e-
H2O
H2
H7O3+
H2O
O2
From DaimlerChrysler
Conductivity depends strongly on water content
Water management - a technical challenge
Too little water => drying out, loss of conductivity
Too much water => condensation, flooding of electrodes
Water
ΔT(40 ºC)
60-70ºC
20-30ºC
90-100ºC
50-60ºC
Cooling a FC car requires a larger cooling system (radiator)
Reformer / Reformer
Brændselscelle / Fuel cell
How can a higher working temperature help ?
El
Nat. Gas,
Methanol
Advantages:
• Higher CO tolerance
• No water management
• No liquid water
• Higher value of excess heat
• Easier cooling
CO-oprensning
til 0,001 %
Varme/heat
H2
CO2
CO
H2
CO2
Befugtning af
luften
Humidification
of the air
CO clean-up
to 0,001 %
Luft ind
Air in
Luft ud
Air out
6
Reformer / Reformer
Brændselscelle / Fuel cell
Other attempts
El
Nat. Gas,
Methanol
CO-oprensning
til 0,001 %
Varme/heat
H2
CO2
CO
H2
CO2
Befugtning af
luften
Humidification
of the air
CO clean-up
to 0,001 %
Luft ind
Air in
Luft ud
Air out
Almindelige PEM-celler er baseret
på membraner som Nafion
Ny
membran
af PBI og
phosphorsyre
Maksimal temperatur:
ca. 80°C
Conventional PEMFC are based
on Membranes like Nafion
Maksimal temperatur:
ca. 200°C
Maximum temperature
ca. 80°C
New membrane of PBI and phosphoric
Replacement of sulphonic acid
- Phosphonic acid
- Other side chains
- Other acceptor/donors
Replacement of water
-H2SO4
-H3PO4
-CF3SO3H
Direct methanol fuel cell (DMFC)
(A special PEMFC)
Anode: CH3OH + H2O → 6H+ +6e- + CO2
Cathode:
1.5O2 + 6H+ + 6e- → 3H2O
acid
Maximum temperature: ca. 200°C
Nafion
PBI
H
N
H
N
N
N
Electrolyte: Ion conducting polymer (e.g. Nafion)
Catalysts: Noble metals (Pt and Pt alloys)
n
Poly (2,2´-m-(phenylene)-5,5´-bibenzimidazole)
7
Direct methanol fuel cell (DMFC)
Size:
DMFC
< 1W - 1 kW
Applications:
• Portable electronics (laptops, phones, MP3...)
• Small/medium UPS systems
• Remote power
DMFC
DMFC
Toshiba
DMFC for
1) a laptop
2) an MP3 player
DMFC
IRD Fuel cells
8
DMFC
DMFC
Direct methanol fuel cell (DMFC)
Example System (bus)
Advantages:
• Liquid fuel
• Easy and fast fuelling
• Easy and compact fuel storage
193 kW
180 kW
Work
166 kW
30%
Motor etc. 14 kW
DC/DC 13 kW
Losses:
Cooler 20 kW
• MeOH poisonous
Power
213 kW
Compr
47 kW
• Expensive catalyst (10xPt amount)
FC el.
260 kW
FC heat
285 kW
Disadvantages:
• Low efficiency
• Fuel crossover
Fuel
545 kW
9
Some of the problems
Polymer fuel cell (PEMFC)
• Cost
• Hydrogen storage in vehicles
• Efficient hydrogen production
• Durability of cells
• Noble metals supply
• Infrastructure
• Numerous technical details
From IRD Fuel cells
10