HiPEM
Optimization of Highly Sulfonated Polysulfones
for Fuel Cell Applications
SO3H
O
S
n
O
H+
Giorgi Titvinidze, Anke Kaltbeitzel, Angelika Manhart and Wolfgang H. Meyer
Max Planck Institute for Polymer Research, Mainz / Germany
rt
the A
f
o
e
Stat
Highly sulfonated polysulfones (s-PSU) are more stable, cheaper
and environmentally more friendly, and methanol crossover is much lower
than in perfluorinated ionomers like Nafion® [1].
The synthesis of s-PSU succeeds via a polysulfide-sulfone precursor [2]:
SO3Na
F
SO2
SO3H
SO 3Na
H2O2
Na2S
[
F
NaSO3
SO2
S
]
n
[
SO2
SO2
]
Acid
n
HOSO 2
NaSO 3
The sulfonation is carried out on the monomer level and the location of the
sulfonation can exactly be predetermined at the electron poor aromatic
ring. It is proven, that the sulfonation at this position is thermally more
stable than at electron rich aromatic rings, as e.g. in polyetheretherketones
(PEEK) [3].
Since s-PSU is made via polycondensation, the polymers usually exhibit
low molecular weights and poor membrane properties.
ion
ivat
Mot
To overcome the disadvantages of state of the art s-PSU
as there are:
- brittleness in the dry state
- high swellability, even water solubility at high IEC
- poor mechanical stability in the swollen state
our work aims at:
- high molecular weight copolymers
- water insoluble polymers with limited swellability
- flexible materials in the dry state
- mechanically stable films in the swollen state
our approach:
n optimization of the polycondensation reaction
o introduction of unsymmetrical monomers
p introduction oft „softly“ branched polymer chains
n optimization of the polycondensation reaction
o introduction of unsymmetrical monomers
The synthesis of the precursor polymer was optimized with variation of X, the „catalyst“,
the solvent, the temperature and the time of the polycondensation reaction as follows:
SO 3Na
n
X
SO 2
X
+m
X
SO2
X
Incorporation of unsymmetrical monomers into the polysulfone chain decreases the
brittleness of dried films and increases mechanical stability of the water swollen films*:
Polymer
GT 73
GT 74
GT 77
GT 78
GT 102
GT 100
Cat
+(n+m) HS
S
SH
Solv. Temp.
NaSO 3
Best results have been reproduced with X = F, 1.3 eq. CaCO3 as „Cat“, with
16 h reflux of toluene to remove water azeotropically, plus 72 h heating in NMP at 185°C:
n
1
1
1
1
1
1
m
0.7
0.7
0.7
0.7
0.4
0
X
F
F
Cl
Cl
F
F
IEC (meq/g)
1.83
1.83
1.83
1.83
2.35
2.78
Mn
152.820
157.780
14.610
15.140
69.180
40.030
Mw
402.260
405.700
20.430
21.370
152.560
106.420
Mn / Mw
2.63
2.57
1.40
1.41
2.21
2.66
l
2
1
1
1
6
4
m
1
1
1
2
3
3
IEC (meq/g)
1.74
1.72
2.01
2.19
2.20
2.32
Mn
37.170
46.070
32.590
42.600
35.710
70.460
Mw
96.990
159.510
79.680
116.580
85.440
128.730
Mn / Mw
2.61
3.46
2.45
2.74
2.39
1.82
* cast from DMF solution
E-Modulus of GT 78 film* at 100% RH at
E 25°C
8
6
*
MPa
Polymer
GT 89/1
GT 89/2
GT 85/1
GT 85/2
GT 99
GT 98
k
3
2
3
4
20
20
elongation
at break:
~ 16,1 %
4
n=k+l+m
With X = Cl and K2CO3 , CsF and other „catalysts“ the molecular weights were much lower.
2
0
0,0
F
SO3Na
kF
SO2
SO2
F
+
l F
SO2
+ n HS
m
S
CaCO3, NMP
1850C
40
SO2
0 75 1 0 % (
l
0.8
0.6
0.4
0
1,5
2,0
2,5
3,0
Temperature / °C
50
60
70
80
90
*
1,00E-02
DC-conductivity at 80% RH
Nafion data from [4]
Water-swollen films are transparent,
flexible and mechanically stable.
n = k + l + 1.5m
IEC (meq/g)
1.74
1.92
2.28
2.75
Mn
47.690
47.300
56.560
48.260
Mw
167.900
170.530
209.080
163.500
Mn / Mw
3.52
3.61
3.70
3.39
Relative Humidity (RH) at 25°C
ions
clus
Con
Highly sulfonated polysulfone copolymers
with high molecular
co
weights and irregular chain structure have been obtained
which form flexible and stable films.
The films are water insoluble and swell heavily under humid
conditions and exhibit conductivities superior to Nafion®.
1,E+00
0
10
20
30
40
50
60
70
80
90
100
1,E-01
Conductivity S/cm
1,E-02
1,E-03
1,E-04
GT84 trans 8x
GT 100 trans 12x
1,E-05
GT 100 long
Nafion long
At RH > 40% some of our films
(GT 84 and GT 100)
exhibit higher conductivities at room
temperature than Nafion®.
These films are mechanically strong
and flexible in the swollen state.
1,E-06
Nafiondata
datafrom
from [5]
[4]
Nafion
e
ratur
Lite
[1] V. Saarinen et al. Solid State Ionic 178, 533-537(2007)
[2] M. Schuster et al, DE Patent 102005010411 (2005)
[3] M. Schuster et al., Macromolecules, 40, 598-607 (2007)
[4] Y. Sone et al., J. Electrochem. Soc., 143, 1254- 1259 (1996)
[5] R. He et al., J. Membrane Sci., 226, 169-184 (2003)
t
men
edge
l
w
no
HiPEM
is a joined project with partners from:
Ack
SO3H
1,E-07
O
MPI for Solid State Research, Stuttgart/Germany (Dr.K.D.Kreuer)
DKI / TU Darmstadt/Germany (Prof.Dr.M.Rehahn)
IPF Dresden/Germany (Dr.J.Meier-Haack)
and is financially supported by the BMBF/Germany, contract # 03SF0323D
S
O
“long“ means:
“trans 8x“ means:
3,5
GT73
GT74
GT77
GT78
Nafion
oxidation
F
l) *
m
0.013
0.012
0.007
0.0075
1,0
GT 100
1,00E-03
O2S
k
1
1
1
1
30
ion-exchange
F
F
Polymer
GT 83
GT 84
GT 103
GT 95
SH
20
1,00E-01
conductivity [S/cm]
Low concentrations of multifunctional monomers lead to softly branched polymers,
which are still soluble and can be cast into films from DMF solution.
The films are flexible in their dry state and are mechanically sufficiently stable also
in their water-swollen state:
NaO3S
0,5
mm
p introduction oft „softly“ branched polymer chains
conductivity measured longitudinal or in plane of the film
conductivity measured transversal or through a package of 8 films
(trans 12x : through 12 films)
Nafion® was measured from 15% RH to 100% RH, our films from wet to dry
n