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Design and Development of High-Performance Polymer Fuel Cell Membranes
Ryo TamakiJoyce HungSteve RiceJoe Suriano
GE Global ResearchMay 16th 2007
Project ID# : FC19
This presentation does not contain any proprietary, confidential, or otherwise restricted information
2007 DOE Hydrogen Program Annual Merit Review / Tamaki 5/16/2007
Project start date: 4/2006
Project end date: 4/2011
Percent complete: 25%
Barriers addressed• Membrane cost• Membrane durability
Total project funding• DOE share: $1.5M• GE share: $0.5M
Funding received in FY06• DOE share: $150k• GE share: $50k
Funding for FY07 • DOE share: $300K• GE: $100K
Timeline
Budget
BarriersOverview
Partners
GE Energy
2007 DOE Hydrogen Program Annual Merit Review / Tamaki 5/16/2007
Objectives
FY06• Design and synthesize new high performance polymer structures• Design and synthesize hydrophilic organic additives• Evaluate membrane performance with and without additives
FY07• Design and synthesize cross-linked system • Prepare high acid density PEM in porous supports• Integrate hygroscopic inorganic additives• Evaluate membrane performance at different relative humidity• Improve chemical and thermal stability
FY08• Improve conductivity at low RH and high temperature (0.1S/cm 50%RH/120°C).
Design and develop novel polymer electrolyte membrane materials for fuel cell operation at high temperature
(up to 120 °C) and low relative humidity (25-50 %RH)
2007 DOE Hydrogen Program Annual Merit Review / Tamaki 5/16/2007
Approaches
• High acid concentration with no leaching• Cross-link chemistry design• Control of the cross-link density• Selection and fabrication of the porous supports• Impregnation• Evaluation of properties
• Improvement in the conductivity, especially at low RH
Gen 1Gen 1
Gen 2Gen 2
Gen 3Gen 3Gen 4 : Cross-linked system in porous supportGen 4 : Cross-linked system in porous support
Hygroscopic additives
Gen 5 : with inorganic additivesGen 5 : with inorganic additives
Copolymer architecture
Cross-linked system in porous support
Introduction of the inorganic additives
• Thermally stable aromatic hydrocarbon polymers • Balance proton conductivities, water uptake, and mechanical properties via material design
2007 DOE Hydrogen Program Annual Merit Review / Tamaki 5/16/2007
Control in copolymer architecture
100 nm100 nm100 nm
Gen 1 : random copolymer
σ ~ 10-3 S/cm (50 %RH)
100 nm100 nm100 nm
Gen 2 : block copolymer
σ ~ 10-2 S/cm (50 %RH)
• Hydrophilic-hydrophobic phase separation is observed in Gen 2.
• The phase separated hydrophobic segment is expected to work as a scaffold and suppress the water uptake.
• Higher conductivity in Gen 2 through formation of efficient hydrophilic channels.
• Hydrophilic-hydrophobic phase separation is observed in Gen 2.
• The phase separated hydrophobic segment is expected to work as a scaffold and suppress the water uptake.
• Higher conductivity in Gen 2 through formation of efficient hydrophilic channels.
2007 DOE Hydrogen Program Annual Merit Review / Tamaki 5/16/2007
Water Uptake
• Water uptake was reduced in Gen3.
• Gen 2 demonstrated conductivity at the same level as Nafion.
• Within Gen 3, higher acid concentration resulted in the higher conductivity.
• Water uptake was reduced in Gen3.
• Gen 2 demonstrated conductivity at the same level as Nafion.
• Within Gen 3, higher acid concentration resulted in the higher conductivity.
020406080
100120140
20 40 60 80 100 120Temperature (°C)
Wat
er U
ptak
e (%
) Nafion 117Gen1Gen2Gen3AGen3B
Conductivity at 80°C
0.0001
0.001
0.01
0.1
0 25 50 75 100 125
% Relative Humidity
Con
duct
ivity
[S/c
m] Nafion 117
Gen1Gen2Gen3AGen3B
2007 DOE Hydrogen Program Annual Merit Review / Tamaki 5/16/2007
Conductivity vs. Water Uptake
0 30 60 90 120 1500.00
0.04
0.08
0.12
0.16
0.20
Con
duct
ivity
at 8
0C a
nd 1
00%
RH
(S/c
m)
Water uptake at 30°C (wt%)
Gen 1Gen 2AGen 2BGen 3Nafion
0 30 60 90 120 1500.00
0.04
0.08
0.12
0.16
0.20
Con
duct
ivity
at 8
0C a
nd 1
00%
RH
(S/c
m)
Water uptake at 30°C (wt%)
Nafion
• Good balance of water uptake and conductivity was achieved in Gen3.
• Further increase in the conductivity is required to meet the Y3 DOE target (0.1S/cm 50%RH/120°C).
• However, higher increase in the acid groups make the polyelectrolyte soluble in water.
• New approaches (Gen 4 and 5) were investigated.
• Good balance of water uptake and conductivity was achieved in Gen3.
• Further increase in the conductivity is required to meet the Y3 DOE target (0.1S/cm 50%RH/120°C).
• However, higher increase in the acid groups make the polyelectrolyte soluble in water.
• New approaches (Gen 4 and 5) were investigated.
2007 DOE Hydrogen Program Annual Merit Review / Tamaki 5/16/2007
Selection of cross-linkable electrolyte unitsCritical factors for the electrolyte units
1. Thermal / oxidative stability2. Acid density3. Controllable cross-link density4. Compatibility with the pore supports
H
HH
H
H
H
H
H
H H
H H H H
H H
H
H
H HH H
H
H
H
H
+
Acid unit Cross-link unit
Number of arms / size
Type / number of
acid groups
Cross-link chemistry
Proton conductivity Morphology
Thermal / oxidative stability
Hydrolytic stability
Dimensional stability
VariablesVariables
PropertiesProperties
2007 DOE Hydrogen Program Annual Merit Review / Tamaki 5/16/2007
Fabrication of cross-linked PEM in porous support
Cross-linked system provides : 1. Increase in acid concentration 2. Dimensional stability3. Thermal stability
Porous support provides : 1. Mechanical strength 2. Dimensional stability3. Thermal stability4. Morphology (hydrophilic channel)
control by template effect
polyelectrolytes
2007 DOE Hydrogen Program Annual Merit Review / Tamaki 5/16/2007
Selection of porous supports
100μm
Pore support APorosity ~45%
Pore support BPorosity ~90%
goodneutralbad
Critical factors A B1. Mechanical strength2. Thermal / oxidative stability3. Porosity / pore size / surface area4. Pore morphology5. Compatibility with the polyelectrolytes6. Scalability 7. Ease of handling8. Cost
2007 DOE Hydrogen Program Annual Merit Review / Tamaki 5/16/2007
Control in the cross-link density – Gen 4A
-Wt loss (100°C/2h) 70%
• Higher conductivity was obtained by incorporating acid units (100%) in a porous support.
• But the electrolyte was extracted out from the support by boiling for 2h due to the high acid concentration and the solubility in water.
• Higher conductivity was obtained by incorporating acid units (100%) in a porous support.
• But the electrolyte was extracted out from the support by boiling for 2h due to the high acid concentration and the solubility in water.
- cross-link chemistry A / acid unit A -
Conductivity at 80 °CConductivity at 80 °C
0.0010
0.0100
0.1000
1.0000
20 40 60 80 100
RH (%)
S/c
m Acid unit-ANafion 112
H
H
Acid unit
2007 DOE Hydrogen Program Annual Merit Review / Tamaki 5/16/2007
Control in the cross-link density – Gen 4AEffect of the cross-linker content on the leaching and the proton conductivity
Extraction at different temperaturesExtraction at different temperatures
• Leaching was suppressed by increasing the cross-linker content.
• The decrease in conductivity with increase in cross-linker content is due to lower acid concentration.
• Leaching was suppressed by increasing the cross-linker content.
• The decrease in conductivity with increase in cross-linker content is due to lower acid concentration.
Conductivity at 80 °CConductivity at 80 °C
-80%-70%-60%-50%-40%-30%-20%-10%
0%10%20%
0.00 5.00 10.00 15.00
[crosslinker] / [acid unit]
wei
ght l
oss
30C60C85C100CTotal
0.0001
0.0010
0.0100
0.1000
1.0000
0.00 5.00 10.00 15.00[crosslinker] / [acid unit]
S/cm
25 %RH100 %RHNafion at 25% RHNafion at 100% RH
H
H
+
2007 DOE Hydrogen Program Annual Merit Review / Tamaki 5/16/2007
Incorporation of inorganic additives – Gen 5A
• Addition of the inorganic additive decreased acid group leaching at low temperatures.• The conductivity improved with the inorganic additive, especially at low RH.
(Exceeds the Y2 DOE target 0.07 S/cm at 80 %RH)• Weight loss was still observed at high temperature and needs to be improved.
• Addition of the inorganic additive decreased acid group leaching at low temperatures.• The conductivity improved with the inorganic additive, especially at low RH.
(Exceeds the Y2 DOE target 0.07 S/cm at 80 %RH)• Weight loss was still observed at high temperature and needs to be improved.
Extraction at different temperaturesExtraction at different temperatures Conductivity at 80 °CConductivity at 80 °C
-60%
-40%
-20%
0%
20%
40%
60%
1 2 3 4 5
Weight Loss
30C60C85C100CTotal
Gen 4A
Gen 5A
-60%
-40%
-20%
0%
20%
40%
60%
1 2 3 4 5
Weight Loss
30C60C85C100CTotal
Gen 4A
Gen 5A
0.0001
0.0010
0.0100
0.1000
1.0000
0 20 40 60 80 100 120
RHS/
cm
Gen4ANafion 112Gen5A
2007 DOE Hydrogen Program Annual Merit Review / Tamaki 5/16/2007
0.0001
0.0010
0.0100
0.1000
1.0000
0 20 40 60 80 100 120
% Relative Humidity
Con
duct
ivity
[S/c
m]
Gen4BNafion 112
Alternative cross-link chemistry – Gen 4B
-Wt loss (100 °C/2h) 0%
H
H
+
Cross-link chemistry
Cross-link chemistry was re-evaluated and optimizedCross-link chemistry was re-evaluated and optimized
• Membrane experiences no leaching.
• The conductivity is comparable to Nafion.
• Membrane experiences no leaching.
• The conductivity is comparable to Nafion.
Conductivity at 80 °CConductivity at 80 °C
2007 DOE Hydrogen Program Annual Merit Review / Tamaki 5/16/2007
0.0001
0.0010
0.0100
0.1000
1.0000
0 20 40 60 80 100 120
% Relative Humidity
Con
duct
ivity
[S/c
m] Nafion 112
R423-15-1R423-17-4R423-17-5R423-17-6R423-17-7R423-17-8R423-17-9
Alternative cross-link chemistry – Gen 4BH
H
+
Cross-link chemistry
• Membrane experiences no leaching.
• The conductivity exceeds Nafion.
• Membrane experiences no leaching.
• The conductivity exceeds Nafion.
Conductivity at 80 °CConductivity at 80 °C
OptimizationOptimizationPorous Support
2007 DOE Hydrogen Program Annual Merit Review / Tamaki 5/16/2007
Alternative cross-link chemistry – Gen 4B
Before acidificationBefore acidification After acidificationAfter acidification
Td = 563°C Td (1) = 285°C Td (2) = 550°C
• Very high thermal stability (Td = 550°C) was achieved.
• No Tg observed before decomposition.
• Very high thermal stability (Td = 550°C) was achieved.
• No Tg observed before decomposition.
2007 DOE Hydrogen Program Annual Merit Review / Tamaki 5/16/2007
0%
5%
10%
15%
20%
25%
30%
35%
40%
Gen 4B Gen 2
XYZ
0%
50%
100%
150%
200%
250%
300%
Gen 4B Gen 2
Alternative cross-link chemistry – Gen 4Bwater uptake and dimensional changes
Water uptake (30°C)Water uptake (30°C) Dimensional changes (30°C)Dimensional changes (30°C)
• High water uptake in Gen4B compared to Gen2.
• Dimensional changes are at the same level as Gen2, but the thickness change for Gen4B is much smaller.
• High water uptake in Gen4B compared to Gen2.
• Dimensional changes are at the same level as Gen2, but the thickness change for Gen4B is much smaller.
Gen 4B
(Cross-linked)
Gen 2
(Not cross-linked)
Gen 2
(Not cross-linked)
Gen 4B
(Cross-linked)
Very small thickness change
2007 DOE Hydrogen Program Annual Merit Review / Tamaki 5/16/2007
Future work FY07/FY08
Materials synthesis• Demonstrate feasibility of cross-linked electrolytes in porous supports• Evaluate the effect of acid/cross-linker ratios on the conductivity• Study the effect of inorganic additives on the conductivity• Evaluate the effect of pore size, porosity and thickness of porous
supports on the conductivity
Membrane evaluation• Evaluate membrane properties (proton conductivity, water uptake,
mechanical properties)
2007 DOE Hydrogen Program Annual Merit Review / Tamaki 5/16/2007
Summary
Relevance : Apply new concepts in polymer membrane design to resolve challenging technical issues related to membrane performance over a wide range of temperatures and humidities.
Approach : Design and synthesize new polymer architectures by formation of the cross-linked electrolytes in porous supports with controlled structures. Explore hygroscopic additives to improve performance at high temperature, low RH.
Progress : Developed completely aromatic hydrocarbon based polymer architectures with concentrated proton conducting functionalities, demonstrating improved balance of water uptake and proton conductivity.
Developed cross-linked electrolytes in porous supports with or without hygroscopic inorganic additives. Demonstrated higher conductivity than Nafionover wide range of relative humidity.
Future research : Continue design and evaluation of new materials. Develop further understanding of the effect of membrane architecture on performance.
2007 DOE Hydrogen Program Annual Merit Review / Tamaki 5/16/2007
Summary Table
Parameters FY06 target FY06 results FY07 target FY07 resultsConductivity (S/cm) 0.07 0.17 0.07 0.11 0.37Temperature (°C) rt 80 rt 80 80RH 100% 100% 80% 80% 100%
Results and DOE high temperature membrane targets
2007 DOE Hydrogen Program Annual Merit Review / Tamaki 5/16/2007
Acknowledgment: “This material is based upon work supported by the Department
of Energy under Award Number DE-FG36-06G0 16034"
Disclaimer: “This report was prepared as an account of work sponsored by an
agency of the United States Government. Neither the United States Government
nor any agency thereof, nor any of their employees, makes any warranty, express
or implied, or assumes any legal liability or responsibility for the accuracy,
completeness, or usefulness of any information, apparatus, product, or process
disclosed, or represents that its use would not infringe privately owned rights.
Reference herein to any specific commercial product, process, or service by trade
name, trademark, manufacturer, or otherwise does not necessarily constitute or
imply its endorsement, recommendation, or favoring by the United States
Government or any agency thereof. The views and opinions of authors expressed
herein do not necessarily state or reflect those of the United States Government or
any agency thereof.”