fuel cells -2fuel cells -2 -...
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Fuel Cells - 2Fuel Cells Fuel Cells -- 22
Jong Hak KimChemical Engineering
Yonsei University
Jong Hak KimChemical Engineering
Yonsei University
Recent Research Trends in Recent Research Trends in Polymer Electrolyte MembranesPolymer Electrolyte Membranes
Fuel Cells Fuel Cells
PEMFC (Proton Exchange Membrane Fuel Cell)DMFC (Direct Methanol Fuel Cell)
Electrolyte
CurrentCollector
CH3OH
Anode
Water Electrical
Circuite-
Cathode
O2
CurrentCollector
Catalyst layer
Water
Electrolyte
CurrentCollector
CH3OH
Anode
Water Electrical
Circuite-e-
Cathode
O2
CurrentCollector
Catalyst layer
Water
H2, CH3OH/H2O H+
ContentsContents
Overview of proton conducting membranes- Structure, Synthesis - Chemical properties- Electrochemical properties- Applications to fuel cell (DMFC, PEMFC)
Membranes- Sulfonated aromatic polymers- Alkylsulfonated aromatic polymers- Acid-base polymer complexes- Block copolymer electrolytes (BCE)- Graft copolymer electrolytes (GCE)
Self-organizing !!!
Background Background -- 11
Perfluorinated polymer electrolytes- Satisfactory properties - High cost (~ $600/m2)- low H+ conductivity at high T & low humidity- high MeOH crossover
Background Background -- 22
Aciplex, Dow membrane- Short side chain - High ratio of SO3H/CF2
- High specific conductivity
GoreSelect membrane- Fine-mesh PTFE support impregnated with Nafion- high mechanical stability ~10μm
PTFE: poly(tetra fluoro ethylene)
Features of Features of PerfluorinatedPerfluorinated PEsPEs
Background Background -- 33
Features of hydrocarbon polymers- Cheap !!!- Low thermal/chemical stability- Life-time can be improved by catalyst, assembly technology
- Contain polar group: high water uptake- Decomposition can be depressed by molecular design
- easily recycled by conventional method
SulfonatedSulfonated Aromatic PolymersAromatic Polymers
Polysulfone (PSf)
Poly(styrene) (PS) Poly(ether ether ketone) (PEEK)
Poly(benz imidazole) (PBI)
Poly(phenylene sulfide) (PPS)Poly(ether sulfone) (PES)
AkylsulfonatedAkylsulfonated Aromatic PolymersAromatic Polymers
Alkylsulfonated PBI
Alkylsulfonated PSU
- Deprotonation of N in BI ring- Reaction of alkylsultone with PBI anion
J. Membr. Sci. 2004, 230, 61.
Macromolecules 1993, 26, 5633.
AcidAcid--Base Polymer ComplexesBase Polymer Complexes
PBI/H3PO4
PEO/strong acid PEI/strong acid
PAAM/strong acid PVA/strong acid
PEO: poly(ethylene oxide), PEI: poly(ethylene imine)PAAM: poly(acrylamide), PVA: poly(vinyl alchol)
Types of Block copolymer
Block CopolymersBlock Copolymers
Phase separated morphology
Block CopolymersBlock Copolymers
- Physical connection by covalent bond
- Immiscible pair: degree of segregation
- Order-disorder transition temperature (ODT)
- Self-assembly in nanometer length scales
Phase Separated Morphology
1/T
Block Copolymer Electrolytes
conducting
nonconducting
H+
H+
H+
H+
Advantages- Formation of ion conducting channels by microphase separation
- Hindering of swelling by surrounding non-sulfonated phase
- Lowering of MeOH permeability- High mechanical stability
High ionic conductivityGood mechanical property
PolystyrenePolystyrene--based BC (1)based BC (1)
Styrene-b-(ethylene-co-butylene)-b-styrene (SEBS)- 0.1 S/cm, bicontinuous structure
Interdomaindistance
~ ion cluster
cf. Nafion~5nm
Comparable conductivity SANS
Macromolecules 2002, 35, 5916
SANS: small angle neutron scattering
PolystyrenePolystyrene--based BC (2)based BC (2)
SEBS - Comparable H+ conductivity (~ 0.1S/cm)- Lower MeOH crossover
Δ: The ratio of conductivity to MeOH permeability
J. Memb. Sci. 2002, 207, 129.
PolystyrenePolystyrene--based BC (3)based BC (3)
Styrene-isobutylene-styrene - hexagonally packed PS cylinder- Upon increase of PS fraction, distance btncylinders unchanged, cylinder diameter change
Block copolymer Ionomer
Polymer, 2000, 41, 3205
Polystyrene based BC (4)Polystyrene based BC (4)
Crosslinked SBS- Structure fixation by UV crosslinking
Macromolecules 2003, 36, 3228
Φ: The ratio of conductivity to MeOH permeability
Membrane properties
Polyimide (1)Polyimide (1)
Block PI : successive step of polycondensation
• 1st step: 1,4,5,8-naphthalene tetracarboxylic dianhydride (NDTA) + 4,4’-diaminobiphenyl-2,2-disulfonic acid (BDSA)
• 2nd step: NDTA + 4,4’-oxydianiline (ODA)
Sep. Pur. Tech. 2001, 22, 681
Polyimide (2)Polyimide (2)
Block PI
Polymer, 2001, 42, 359
Aromatic diaminesNDTA BDSA
Polyimide (3)Polyimide (3)
Property: Conductivity, morphology
Polymer, 2001, 42, 359
• Low ionic conductivity ~ few mS/cm • Presence of large ionic domains by SANS
SANS
PolyaramidesPolyaramides
Polyaramide- Swelling is restricted by non-sulfonated domains - not stable at high T (135 oC) due to desulfonation, hydrolytic cleavage of amide bonds.
React. Funct. Polym. 2003, 57, 77
Poly(etherPoly(ether sulfonesulfone) (1)) (1)
Sulfonated BC- Silyl method in NMP/K2CO3 at 150 oC
Macromol. Symp. 2004, 210, 175
Hydrophobic Hydrophilic
TMS: trimethylsilyl
Poly(etherPoly(ether sulfonesulfone) (2)) (2)
Conductivity, DMFC performance - lower conductivity, but comparable cell performance
Macromol. Symp. 2004, 210, 175
Due to low MeOH crossover and lower thickness of membrane
PEEKPEEK
Nucleophilic aromatic substitution
J. Membr. Sci, 2004, 234, 75
high conductivity
low MeOH permeability
Block Copolymer Block Copolymer IonomerIonomer
Two-stage process: Nucleophilic substitution
J. Membr. Sci. 2004, 245, 147
Phase separation leads to physical crosslinking
End-functionalized hydrophobic blocks
Block Copolymer Block Copolymer IonomerIonomer
Cell performance
J. Membr. Sci. 2004, 245, 147
PEMFC DMFC
Good stability, acceptable performance during the operation
NitroxideNitroxide--mediated Living Radicalmediated Living Radical
Styrene-b-styrenesulfonic acid
Polymer 2002, 43, 3155
DEPN: 2,2,5,5-Tetramethyl-4-phosphono-3-azahexane-3-nitroxide
Polymerization of SSPEN or SSBu
Transformation to sulfonic acid
Block copolymerization
Graft CopolymerizationGraft Copolymerization
• Types of high energy radiations
1) Electromagnetic radiation- γ-ray, x-ray (Co-60; radioactive isotope, Cs-137; γ-ray source)
2) Particulate radiation (charged particle)- electron, swift heavy ions- from accelerator
• Radiation (γ-ray, electron beam)- chain grafts are covalently attached to main chain
• Polymer backbone is irradiated in the presence of monomer (vap. liq. bulk, solution)
• In air, N2 or under vacuum
Simultaneous Irradiation Method
1) Mutual recombination
DeactivationDeactivation
P· : primary radical of polymer backbone
2) Homopolymerization
1) Irradiation of polymer to form active radical2) Contact with monomer
PrePre--irradiation methodirradiation method
• Vac./inert atmosphere
• O2 atmosphere
RadiationRadiation--induced graftinginduced grafting
• Broad, promising technique
• Reaction parameter:- dose / dose rate- type or concentration of monomer- type of polymer film- type of additive(diluent, inhibitor, acid, x-agent)
- temperature
Graft CopolymerizationGraft Copolymerization
Grafting of PS onto PTFE
Prog. Polym. Sci. 2004, 29, 499
Graft Copolymer ElectrolytesGraft Copolymer Electrolytes
Membrane property
J. Membr. Sci. 2005, 251, 121
Base polymers
ETFE: poly(ethylene tetrafluoroethylene, PVDF: poly(vinylidene fluoride)LDPE: low density polyethylene
Basic grafting scheme
Graft Copolymer ElectrolytesGraft Copolymer Electrolytes
Superior DMFC performance
J. Membr. Sci. 2005, 251, 121
LDPE PVDF
Graft Copolymer ElectrolytesGraft Copolymer Electrolytes
Grafting of GMA onto PE
Prog. Polym. Sci. 2004, 29, 499J. Electrochem. Soc, 1996, 143, 2795
GMA: glycidyl methacrylate
CrosslinkedCrosslinked Graft CopolymerGraft Copolymer
Crosslinking with DVB
Crosslinking agent
J. Membr. Sci. 2003, 216, 27
(DVB)
PFA-g-PS/DVB-SO3H Membrane
PFA: poly(tetrafluoroethylene-co-perfluorovinyl ether)
CrosslinkedCrosslinked Graft CopolymerGraft Copolymer
Membrane properties
J. Membr. Sci. 2003, 216, 27
- High conc. of DVB reduce water uptake and ionic conductivity
- Thermal stability (decomposition of SO3H) is not affected by crossliking
Commercial Graft MembranesCommercial Graft Membranes
Commercial Membranes
• Permion: irradiation grafting of styrene onto FEP (or PTFE, ETFE)
• Raymion: pre-irradiation grafting of trifluorostyrene onto ETFE,
followed by sulfonation
J. Electrochem. Soc. 1998, 145, 780
• comparable performance with Nafion 117
• ~ 10,000h stability
FEP: poly(tetrafluoroethylene-co-hexafluoropropylene)PTFE: poly(tetrafluoro ethylene)ETFE: poly(ethylene tetrafluoroethylene)
Living Graft copolymerLiving Graft copolymer
PVDF-g-PVBC-PS by ATRP
J. Poly. Sci. Poly. Phys. 2002, 40, 591
PVBC: poly(vinylbenzyl chloride)
Electron-beam preirradiation grafting => atomic transfer radical polymerization (ATRP)
Promising materials for fuel cells !!!
Living Graft copolymerLiving Graft copolymer
TEMPO mediated polymerization
Macromolecules 2004, 37, 9909
TEMPO: 2,2,6,6-tetramethylpiperidinyl-1-oxy, PSSA: poly(styrene sulfonic acid)
PVDF-g-PSSA
Preliminary H2/O2 fuel cell tests show promise for PEM
Block Copolymer
Partially fluorinatedHydrocarbon
Closing RemarkClosing Remark
Graft Copolymer
Future Direction to Polymer Electrolytes
MATERIALS
STRUCTURE