Simon Fraser University researchers developed novel polymer membranes for fuel cells. They synthesized fluoropolymer-block-ionic and fluorous-ionic graft copolymers with different architectures. The membrane morphology, including ionic channel size and continuity, depended on polymer structure and affected properties like water uptake and proton conductivity. Fully sulfonated membranes showed continuous increases in proton conductivity with ion exchange capacity, while partially sulfonated membranes peaked at moderate capacities due to conductivity drops at high capacities. The graft structure allowed high capacities without dissolution, promising for low-humidity proton conductivity needed in fuel cells.

1. Simon Fraser University

2. Model Polymers for Fuel Cell Membranes.
E.M.W. Tsang, A. Yang, Z. Shi,
T. Weissbach, R. Narimana,# B. Frisken,#
S. Holdcroft*
Dept. of Chemistry (Physics#)
Simon Fraser University
Burnaby, British Columbia
Canada
Dec, 2013,
ICAER 2013
Funding:
2

3. Proton Exchange Membrane Fuel Cell (PEMFC)
eProton Exchange
Membrane (PEM)
HO
2
e-
Anode Reaction
Cathode Reaction
2H
4H ++ 4e 2
(Hydrogen)
H+
H
2
Catalyst
O + 4H ++ 4e2
O
2
Electrode
2H O
2

4. Fuel Cells – Stacks
Bi-polar plate
Automotive: 80,000 W
~350-400 MEAs
750 Bipolar plates
flow field
MEA
electrode
backing
gasket

5. Structure of Nafion (PFSI)
CF2
CF2
x
CF
CF2 y
OCF2CF z O(CF2)2SO3H
CF3
1 micron (1/1000 mm)

6. Perfluorinated vs Hydrocarbon PEMs
Advantages
••
••
••
••
••
High proton conductivity
High proton conductivity
Efficient even at low operating temp
Efficient even at low operating temp
Good mechanical properties
Good mechanical properties
High durability
High durability
Good flexibility at low temp
Good flexibility at low temp
Disadvantages
••
••
••
••
Very expensive
Very expensive
High H22,O22,, N22 & methanol crossover
High H ,O N & methanol crossover
Humidification necessary
Humidification necessary
Failure at high temperature (( >100
Failure at high temperature >100
0C)
0C)
Catalyst poisoning
•• Catalyst poisoning
•• High electro-osmotic drag
High electro-osmotic drag
There is a need to develop alternative advanced membranes based on
aromatic hydrocarbons
6

7. Potential Polymer Architectures for PEM Materials
F2
C
CF2CF2
CFCF2
x
OCF2CF
Nafion
CF3
x
y
OCF2CF2SO3H
H2
C
CH2
C
CF2
CH2
ETFE-g-PSSA
y
z CH2
CH2
z
SO3H
SO3H
Examples of
PEMs
O
HO3S
CF2 CF
O
C
O
CF2 CF
n
m
n
CH2CH
CH2 CH
R
SO3H
S-PEEK
CH2 CH2
CH3 CH2
CH2CH
BAM
CH2 CH
CH2CH3
S-SEBS
SO3H
SO3H
7

8. Microphase Separation in Block Copolymers
F.S. Bates and G. H. Fredrickson, Physics Today, Feb. 1999.
Block
Copolymers
Graft
Polymers

9. Synthesis of Novel Fluoropolymer-blockIonic Polymers
R-X
x CF2=CH2 + y CF2=CF-CF3
Chain Transfer
Radical Polymerization
CH2CF2 x CF2CF y
CF3
Macroinitiator
R'-X
n
CuX / bpy
CH2CF2 x CF2CF y
CF3
CH2CH n X
ATRP
ClSO3H or CH3COOSO3H
Sulfonation
CH2CF2 x CF2CF y
CF3
CH2CH n X
SO3H
•
•
•
Chain Transfer Radical Emulsion
Polymerization
Atom Transfer Radical
Polymerization
Sulfonation
20%HFP
80%VDF
HFP
VDF

10. Synthesis of Fluorous-Ionic Graft
Copolymer
P(VDF-co-CTFE)-g-SPS
x CF
CH
2
2
+
y CF
2
E m ulsion P olymerization
CF
*
CH2CF2
Na S O + K S O
2 2 5
2 2 8
Cl
2.6mol%CTFE
97.4mol%VDF
CuCl / bpy
x
CF2CF
y
CF2CF
Cl
P(VDF-co-CTFE)-g-PS
*
S ulfona tion
z
CH2CH
Cl
n
*
y
P(VDF-co-CTFE)
Macroinitiator
n
CH2CF2
CF2CF
Cl
AT R P
*
x
CH3COOSO3H
*
CH2CF2
x
CF2CF
y
CF2CF
Cl
*
z
CH2CH
Cl
n
P(VDF-co-CTFE)-g-SPS
SO3H
10

11. Membrane Morphology
Diblock copolymer:
H
CH2CF2
x'
Graft copolymer:
CF2CF
CH2CH
y'
n'
CF3
CH2CF2
x
CF2CF
Cl
y
CF2CF
z
CH2CH
SO3H
n
SO3H
100 nm
Perforated Lamellar Morphology:
- “Ionic” channels width = 8 – 15 nm
11
100 nm
Disordered cluster-network Morphology:
-Ionic cluster size = 2 – 3 nm
Note: Nafion cluster size = 5 – 10 nm

12. Diblock vs Graft Membrane
Diblock copolymer:
Graft copolymer:
100 nm
100 nm
-
120
90
60
30
0
0.08
0.06
0.04
0.02
0.00
0.0
0.5
1.0
1.5
2.0
2.5
IEC (mmol/g)
Grafts (small ionic clusters):
0.0
0.5
1.0
1.5
2.0
IEC (mmol/g)
- Less water swelling  Lower proton mobility
- Maintain good mechanical property and high
proton concentrations
2.5
1.2
2.5
1.0
2.0
0.8
1.5
0.6
1.0
0.4
0.5
0.2
0.0
x 103 (cm2 s-1 V-1)
dissolves
150
3.0
eff
Proton Conductivity (S/cm)
0.10
0.0
0.0
0.5
1.0
1.5
2.0
2.5
IEC (mmol/g)
Diblocks (long-range channels):
- Greater water uptake  Higher proton
conductivity and mobility
- Excessive water swelling  mechanical
instability and limited attainable IEC.
[H+] (M)
H2O]/[SO3 ])
180

13. 6-17% PS, Fully Sulfonated
Proton Conductivity :
35% PS, p. Sulfonated
(IONIC PURITY):
6-17% PS, Fully Sulfonated:
45% PS, p. Sulfonated
B
50% PS, p. Sulfonated
100 nm
35% PS, Partially Sulfonated:
E
100 nm
45% PS, Partially Sulfonated:
H
Proton Conductivity (S/cm)
0.12
6-17% PS, fully sulfonated
35% PS, partially sulfonated
45% PS, partially sulfonated
50% PS, partially sulfonated
Nafion 117
0.10
0.08
0.06
0.04
0.02
0.00
100 nm
50% PS, Partially Sulfonated:
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
IEC (mmol/g)
J
100 nm
- Fully sulfonated : continuous increase in
proton conductivity with IEC
- Partially sulfonated: initial increase followed
13
by drop in proton conductivity at high IEC.

14. Fluorinated polymer
Partially Sulfonated polystyrene
& water
SANS: Contrast Variation Effect
100 nm
Rubatat, Holdcroft, Diat, Shi. Frisken

15. Conclusions
IEC = 0.70 mmol/g
•
•
•
•
G
K
C
100 nm
IEC = 0.68 mmol/g
100 nm
IEC = 0.89 mmol/g
100 nm
500 nm
Model fluorous-ionic diblock copolymers with different block ratios have been
synthesized to investigate structure-property relationships in PEMs.
Water sorption, proton conductivity, proton mobility, anisotropy, etc, depend
strongly on the membrane morphology….and on the degree of sulfonation within
an “ionic” channel.
Ionic purity of the “ionic channel” is critical.
The graft structure allows for very high IEC without dissolution – promising for
low RH conductivity.

16. T.J. Peckham, S. Holdcroft. Adv.
Mater., 22 (2010) 4667–4690
Yossef Elabd and Michael Hickner
“Block Copolymers for Fuel Cells”
Macromolecules, 2011, 44 (1), pp 1–11