2004 DOE Hydrogen, Fuel Cell and Infrastructure ......2004 HFCIT Program Review May 25 , 2004 2004...
Transcript of 2004 DOE Hydrogen, Fuel Cell and Infrastructure ......2004 HFCIT Program Review May 25 , 2004 2004...
2004 HFCIT Program Review May 25 , 2004
2004 DOE Hydrogen, Fuel Cell and InfrastructureTechnologies Program Review
High Temperature Polymer Electrolytes Based onIonic Liquids
Robert GilbertsonYu Seung Kim E. Bruce Orler
Bryan Pivovar, Point of Contact
Los Alamos National Laboratory
DOE Program Manager: Nancy Garland LANL Program Manager: Ken Stroh
This presentation does not contain any proprietary or confidential information.
2004 HFCIT Program Review May 25 , 2004
Overall Objective: Contribute to DOE effort in developing hightemperature polymer electrolytes for transportation applications.
Specific goals:• Increase conductivity at high temperature (~120˚C) and low relative
humidity (<50% RH)• Improve fundamental understanding of conduction in ‘free’ proton
containing ionic liquids• Develop robust polymer systems• Probe the dependence of properties on ion capacity, water content
and temperature
• FY04 Budget: 300 K$
Project Objectives
2004 HFCIT Program Review May 25 , 2004
Technical Barriers and Targets
O. Stack Materials and Manufacturing Cost
P. DurabilityR. Thermal and Water Management
While issues involving cost and durability exist, Thermal andWater Management is the primary driver for this task.
12012080˚COperating Temp.
>5000>40001000hrsDurability
550$/kWCost
0.10.10.1S/cmConductivity
201020052000
DOE High Temperature Membrane Working Group Technical Targets
2004 HFCIT Program Review May 25 , 2004
• Investigate ionic liquids based on imidazole cations anddihydrogen phosphate (H2PO4
-) or bisulfate (HSO4-) anions
capable of proton conduction in high temperature membranes
• Advantages of ionic liquids are– Thermally stable (up to 300 ˚C)– Stable to oxidation and reduction– Essentially no vapor pressure– High intrinsic ionic conductivity
• Investigate conduction limits of these materials, incorporatethe most promising candidates into polymeric materials.
LANL Approach
2004 HFCIT Program Review May 25 , 2004
FY ’04 Milestones and Progress:
Nov 03: Screen functionalized imidazole-acid pairs for target materials Status: Many (>10) imidazole-acid pairs have been synthesized
and screened.
Feb 04: Characterize water and temperature dependence on conductivity. Status: Characterization of 4 imidazole-acid pairs.
Sep 04: Synthesize and test polymers/oligomers based on target materials. Status: First generation polymers already synthesized and tested,
second generation block copolymers being synthesized.
Project Timeline
Investigation of proton containing ionic liquidsbegan in February of 2003.
2004 HFCIT Program Review May 25 , 2004
N N+ Cl–
K[HSO4]
+
N N+
KCl
HSO4–
+
CHCl3, RT
N N+ Cl–
K[H2PO4]
+
N N+
KCl
H2PO4–
+
100˚ C
• Mixture is filtered to eliminate bulk of KCl
• Residual KCl removed by precipitation from chloroform
• Solid reaction product is extracted into methanol and filtered
• Methanol is removed under vacuum and residual KCl
removed by precipitation from CHCl3
Ionic Liquids
Ethyl Methyl Imidazolium (EMI) Salts
Acid-Imidazole Pairs
• ‘Free’ proton containing acid-imidazole pairs synthesized
• Pairs characterized in terms ofproperties (melting point,conductivity, stability, etc.)
2004 HFCIT Program Review May 25 , 2004
0
20
40
60
80
100
Weig
ht (%
)
0 200 400 600 800 1000
Temperature (°C)
––––––– EMI/HSO4––––––– EMI/H2PO4– – – – I/HSO4– – – – I/H2PO4
Universal V3.8B TA Instrumen
Nitrogen PurgeHeating rate 10oC/min
Imidazole-acid pairsstudied by TGAshowed thermalstability to at least200C, adequate forhigh temperaturemembraneapplications
Thermal Stability
2004 HFCIT Program Review May 25 , 2004
103 T
-1 (K
-1)
2.4 2.6 2.8 3.0 3.2 3.4 3.6
(S/
)
0.002
0.005
0.01
0.02
0.05
0.1
0.2
T (oC)
140 120 100 80 60 40 20
1: I/HSO4 in water (53%)
2: EMI/HSO4 in water (29%)
3: 4-MI/H2PO4 in water (53%)
4: EMI/H2PO4 anhydrous
1
2
3
4
Conductivity Dependence on
Temperature
• Conductivity of acid-imidazolepairs (even water-free) washigh and suggest further studyis merited
• Pairs showed Arrheniusconductivity dependence
• Conductivities representconductivity of all ionicspecies, NMR or othertechniques needed todetermine protoniccontribution
2004 HFCIT Program Review May 25 , 2004
103 T
-1 (K
-1)
2.4 2.6 2.8 3.0 3.2 3.4 3.6
(S/
)
0.005
0.01
0.02
0.05
0.1
T (oC)
140 120 100 80 60 40 20
1: I/HSO4 in water (53%)
2: I/HSO4 in water (62%)
3: I/HSO4 in water (73%)
4: 4-MI/H2PO4 in water (53%)
5: 4-MI/H2PO4 in water (62%)
6: 4-MI/H2PO4 in water (73%)
123
4
5
6
Influence of Water Content on Conductivity
• Conductivity of acid-imidazolepairs was found to increasewith water content andtemperature within the rangeshown here
• Conductivities limited to 100Cdue to experimental apparatus
• Acid-imidazole pairs are veryhygroscopic and retainedwater may prove critical inimproving conductivity
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Polymer Route
We have generated and first generationpolymer films based on norbornenechemistry (above).Other chemistry such as ether precursorscan be easily incorporated into polymersusing similar techniques (left).
Polymer Synthesis
2004 HFCIT Program Review May 25 , 2004
• Well defined polymers – low polydispersity
• Easy to make block copolymers
• Different types of polymerization mechanisms givematerials with different properties
• Readily available monomers and catalysts
• Can be functionalized with little difficulty
While chemical stability of backbone needs to be studied,this architecture allows us to study performance in wellcontrolled morphologies with target functionality.
Why use Polynorobornenes?
2004 HFCIT Program Review May 25 , 2004
Synthesis of exo Monomers
• Synthesis of poly-norbornene was limitedby the endo isomer
• The exo isomer wasisolated
• The exo isomer can thenbe functionalized to givea monomer that yieldsreasonable molecularweight polymer
• Reaching this step tooksignificant effort
2004 HFCIT Program Review May 25 , 2004
Norbornene Polymerization
• We havesynthesizedpolymers ofreasonablemolecular weightand film castingproperties
• Very few polymerchemistries havebeen explored(copolymers,density or type offunctional groups,etc.)
2004 HFCIT Program Review May 25 , 2004
Initial tests showed surprisingly highconductivity, albeit far below Nafion. Furtherwork needs to be done to verify these results.
AC Impedance SpectroscopyPNBA-2-MI in liquid water
PNBA-2-MI poly-dihydro(norbornene-2-carboxy-N-(1-methyl-1H-imidazol-2-ylmethyl)-amide)
0
0.005
0.01
0.015
0.02
20 40 60 80
Temperature (C)
Co
nd
uc
tiv
ity
(S
/cm
)
water uptake is high (45%)and this particular membraneis water soluble when dopedwith acid.
Hydrated Membrane Conductivity
2004 HFCIT Program Review May 25 , 2004
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0 20 40 60 80 100
Temperature (C)
Co
nd
ucti
vit
y (
S/c
m)
Membrane Conductivity Dependence onWater Content
• PNBA-2-MI phosphate is water soluble, butshows reasonable conductivity even in the drystate
• The role of the phosphate anion and proton inconduction needs to be clarified
PNBA-2E5MI
• PNBA-2E5MI is the ethylated version of PNBA-2-MI and is also water soluble, but likewise showsreasonable conductivity at low RH
PNBA-2-MI
25%0.047 S/cm
10%0.035 S/cm
Relative HumidityConductivity (90˚C)
2004 HFCIT Program Review May 25 , 2004
Thermal Analysis
• Methyl imidazoleevaporates at low T (30˚C)
• Methyl imidazole –dihydrogen phosphateshows mass loss atmoderate T (150˚C)
• Polymer analogues showgood temperature stabilityto at least 200˚C for theacid analogue, 300˚C forneutral polymer
2004 HFCIT Program Review May 25 , 2004
• Imidazole-acid pairs show reasonable conductivity athigh temperatures even at low humidity, while stillexhibiting good thermal stability
• We have successfully synthesized and characterizednorbornene tethered ionic liquids
• The resulting polymers are thermally stable up to atleast 200 ˚C
• While water solubility is a concern, conductivity datafor the films is very promising
• The role of the anion versus the proton in ionconduction needs to be elucidated
Conclusions
2004 HFCIT Program Review May 25 , 2004
• Continued work on imidizole-acidpairs (further characterization ofwater and temperature effects)
• Copolymers (random and block)investigated for control of wateruptake properties
• Investigation of tethered acidicmoeities compared to free acids
• Incorporation of alternateimidazole functionality into thepolymer
• Chemical stability in fuel cells
Future Work
2004 HFCIT Program Review May 25 , 2004
Collaborations and Interactions
1. Lawrence Berkeley National Laboratory: John Kerr -
developing high temperature ionic liquid based technology on
battery electrolytes.
2. Virginia Polytechnic and State University: James McGrath –
characterization and testing of MEAs for high temperature
applications.
2004 HFCIT Program Review May 25 , 2004
Project Safety
Management Safety Controls• Hazard Control Plan (HCP): Hazard based safety review.
• Integrated Work Document (IWD): Task based safety review.
• Relevant safety courses and OJT required for lab work.
• Integrated Safety Management (ISM).
Define work Analyze hazards Develop controls Perform work Ensure
performance
Engineering Controls• Hydrogen cylinders contain less than the LEL for full release into
the room.
• Thermal barriers are commonly used to prevent burns.
• Two man rule employed for any ‘energized’ work.