resonance-stabilized anion exchange polymer electrolytes · resonance-stabilized anion exchange...
TRANSCRIPT
1
Resonance-Stabilized Anion Exchange Polymer Electrolytes
Yu Seung Kim ([email protected])
Los Alamos National Laboratory Los Alamos, NM, 87545
Project ID: FC043
2012 U.S. DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review and Peer Evaluation Meeting May 14-18, 2012, Washington, D.C.
This presentation does not contain any proprietary, confidential, or otherwise restricted information
2
Timeline
Project start September 2009
Project end March 2012
Percent complete 100%
a. Polymer & ionomer synthesis (100%)
b. Catalyst preparation (100%)
c. MEA processing & testing (100%)
d. Degradation study (100%)
Budget
Total funding $ 1,320 K
Funding for FY10 $ 528 K
Funding for FY11 $ 330 K
No cost shared
Barriers
B. Cost
C. Electrode performance
A. Durability
Overview
Partners
Project lead Los Alamos National Laboratory Yu Seung Kim (PI)
Dae Sik Kim Andrea labouriau Hoon Jung
Subcontractor
Sandia National Laboratory Cy Fujiomoto (Ext. PI) Michael Hibbs
Jet Propulsion Laboratory Charles Hays (Ext. PI) Daniel Konopka Michael Johnson Michael Errico Poyan Bahrami
Interactions Cellera Technologies (Shimpshon Gottesfeld)
Advanced Industrial Science and Technology (Yoong-Kee Choe) Ovonic Fuel Cells (Rob Privette)
2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review
3
Relevance – Objectives, Technical Barriers, Technical Targets and Results
Demonstrate an improved alkaline membrane fuel cell (AMFC) performance and durability using advanced polymer electrolyte membranes, ionomers and non-precious catalysts
Major tasks
FY 09 & 10: Synthesis of anion exchange membranes and ionomers
FY 10 & 11: Characterization of catalyst and AMFC performance
FY 11 & 12: AMFC durability test and durability mechanism
ISSUES Technical Barriers Technical Target a FY 09-10 FY 10-11 FY 11-12 Result
Membrane Conductivity Stability Tensile properties
: > 50 mS/cm > 500 h in NaOH soln. 60 C Stress: > 10 MPa, Strain : > 10%
× ×
×
120 mS/cm 672 h
25 MPa, 30%
Ionomer Backbone structure Conductivity Stability
Perfluorinated > 50 mS/cm 20 mS/cmb > 500 h in NaOH soln.
×
–.
–
×
M-Nafion®-FA-TMG 20 mS/cm
7% after 72 h
Catalyst Element ORR activity
Non-precious metal or carbon > 0.9 V (E1/2)
– –
CNT/CNP cat. 0.95 V (E1/2)
AMFC per-formance
Maximum power Durability
> 200 mW/cm2 in H2/Air < 10% for 800 h
– –
–
×
466 mW/cm2
~50% for 300 hc
Technical Barriers, Targets and Results
a Values in the original proposal b Conductivity target for ionomer was lowered as we achieved MEA performance target with low conductive ionomers c Mostly due to the cation stability and water management issue; ionomer and polymer backbone degradation is negligible
Objectives
2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review
4
Strain (%)
NF-PAES
0 20 40 60 80 100
Str
ess
(M
Pa)
0
20
40
60
F-PAE
0 20 40 60 80 100
Str
ess
(M
Pa)
0
20
40
60 ATM-PP 1
0 20 40 60 80 100
Str
ess
(M
Pa)
0
20
40
60
Col 15 vs Col 16
Col 17 vs Col 18
Col 19 vs Col 20
ATM-PP 2
0 20 40 60 80 100
Str
ess
(M
Pa)
0
20
40
60
ATM-PP 3
0 20 40 60 80 100
Str
ess
(M
Pa)
0
20
40
60
90% RH
50% RH
10% RH
Strain (%)
Synthesis of Polyaromatic Anion Exchange Membranes for Durability Study
High molecular weight polyaromatic AEMs were prepared
Mechanical properties of the AEMs are strongly influenced by chemical structure and molecular weight
Highlight: Stress: > 25 MPa & Elongation: > 30% at 50% RH
Membrane mechanical milestone (> 10 MPa stress & 10% strain) achieved with F-PAE, NF-PAE and ATM-PP 3
Sample Coun-ter ion
Mw×103 a
(g/mol)
IEC (meq./g)
WU (wt.%)
b
(mS/cm)
F-PAE Cl- 150 2.5 99 46
NF-PAES Br- 87 2.2 43 15
ATM-PP1 Br- 61 1.7 72 30
ATM-PP 2 Br- 77 1.6 64 35
ATM-PP 3 Br- 196 1.7 70 37
Synthesis and properties of polyaromatic AEMs
a measured by GPC using the parent polymers b measured at 80 C using salt form membranes
Stress-strain behavior of AEM parent polymers
measured at 50 C under controlled RH conditions
2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review
BTMA : Benzyl TetraMethyl Ammonium
5
0 10 20 30 40 50
0
5
10
15
20
25
a
de
f
ATM-PP 3 NF-PAES
Strain (%)
0 5 10 15 20 25 30 35
0
10
20
30
40
50
a
b
c
d
9609801000102010401060
NF-PAES c
C-H
1320135013801410
Ab
so
rban
ce
O-H C-O
C-O
C-H, S=O
NF-PAES b
NF-PAES d
NF-PAES a
C-H
Aryl-Ether Cleavage of Poly(arylene ether) AEMs*
FTIR results indicated phenol formation of poly(arylene ether) (PAE) based AEMs after membrane treatment Nucleophilic displacement takes place in the aryl-ether linkage of the PAE backbones
Mechanical properties of the AEMs are greatly influenced by the AEM backbone degradation
Highlight: No backbone degradation observed in poly(phenylene) AEMs
Proposed backbone degradation mechanism
Nucleophilic displacement of aryl-ether linkage
Mechanical property change after membrane treatment
Membrane treatment a: 0.5 M HCl (or HBr) for 30 min (or 2 h); b: 0.1 M NaOH for 1 h, room temp. after a;
c: 0.5 M NaOH for 30 min, room temp. after a d: 0.5 M NaOH for 1 h, 80 C after a e: 0.5 M HCl (or HBr) for 30 min (or 2 h) after d f: 0.5 M NaOH for 1 h 80 C after e g: 0.1 M NaOH for 2 h & 0.5 M NaOH for 100 h at 80 C
131013301350
Ab
so
rba
nc
e
9609801000102010401060
F-PAE a
F-PAE b
F-PAE c
F-PAE d
C-H
C-O C-O O-H C-H C-H C-H
Phenol formation (FTIR) after treatment
F-PAE
0 5 10 15 20 60 80 100
Str
ess (
MP
a)
0
10
20
30
40
50
a
b
c
d
e
Polymer Degradation
2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review
wavenumber (cm-1
)
96098010001020104010601320135013801410
Ab
so
rba
nc
e
C-O
C-O
C-H
ATM-PP bATM-PP c
ATM-PP d
ATM-PP g
O-H C-H
C-H
*C. Fujimoto et al. manuscript was submitted 2012
6
ATM-PP 3
time (h)
0 50 100 150 200 250 300c
urr
en
t d
en
sit
y (
A/c
m2)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
HF
R (
Oh
m c
m2)
0.0
0.2
0.4
0.6
0.8
1.0
F-PAE
0 50 100 150 200 250 300
cu
rre
nt
de
ns
ity (
A/c
m2)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
HF
R (
Oh
m c
m2)
0.0
0.2
0.4
0.6
0.8
1.0
Impact of Polymer Structure on AMFC Performance*
The AEMs having low Mw (ca. < 100 K) showed poor AMFC performance due to the possible interfacial failure during MEA processing
Negligible interfacial issue for high Mw F-PAE and ATM-PP
F-PAE MEA showed catastrophic failure at 55h probably due to the AEM degradation
Highlight: No catastrophic failure for ATM-PP 3 MEA during 300 h life test
Effect of backbone degradation# Effect of molecular weight on AMFC performance
Polymer Degradation
Sample F-PAE ATM-PP1 ATM-PP 2 ATM-PP 3
Mw×103 a (g/mol) 150 61 77 196
HFR ( cm2) 0.23 1.67 1.23 0.21
Membrane: fluorinated poly(arylene ether) AEM (F-PAE, LANL) and poly(phenylene)-based AEMs with
three different molecular weight (ATM-PP, SNL); Test conditions: H2/O2 at 80 C
current density (A/cm2)
0.0 0.1 0.2 0.3 0.4 0.5 0.6
ce
ll v
olt
(V
)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
po
we
r d
en
sit
y (
W/c
m2)
0.00
0.05
0.10
0.15
0.20
0.25
F-PAE
current density (A/cm2)
0.0 0.1 0.2 0.3 0.4 0.5 0.6
ce
ll v
olt
(V
)0.0
0.2
0.4
0.6
0.8
1.0
1.2
po
we
r d
en
sit
y (
W/c
m2)
0.00
0.05
0.10
0.15
0.20
0.25
ATM-PP 1
ATM-PP 2
ATM-PP 3
Membrane: F-PAE and ATM-PP 3; Test conditions: H2/O2 at constant
voltage of 0.3 V, at 80 C
# supporting information for analysis methodology
*C. Fujimoto et al. manuscript was submitted 2012
a measured by GPC using the parent polymers
7
Stability of Perfluorinated Anion Exchange Ionomers
Phenyl guanidinium has much better stability than sulfone guanidinium under high pH conditions
Trace of degradation after the treatment for phenyl guanidinium functionalized perfluorinated ionomers is due to the hydrolysis of amide group rather than polymer backbone or cation degradation
Highlight: Stable perfluorinated ionomers were prepared by introducing electron donating spacer
Ionomer milestone (perfluorinated ionomer with conductivity > 20 mS/cm and stability) achieved
Sample IEC (meq./g)
WU (wt.%)
a
(mS/cm)
FY 11-12 M-Nafion®-FA-TMG 0.70 10 20
FY 10-11 M-Nafion®-TMG 0.90 18 45
Synthesis and properties of perfluorinated AEMs
a measured with hydroxide form at 80 C
Stability after soaking in 0.5 M NaOH at 80 C
1 2
3,4
Carbons in perfluoro carbon
Solid state 13C NMR
wavenumber (cm-1
)
1200140016001800
Tra
nsm
itta
nce
CNCO CH3
wavenumber (cm-1
)
1200140016001800
CN CH3
Before after 24 h
Before after 72 h
FY 11-12 FY 10-11
Polymer Degradation
2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review
8
Stability of Benzyl Tetramethyl Ammonium Cations (ex-situ)
Benzyl tetramethyl ammonium (BTMA) is stable at 60 C; However, ~ 10 % IEC loss after 9 days at 90 C was observed under high pH conditions
Anion conductivity loss of BTMA functionalized F-PAE and ATM-PP 3 was observed at 0.5 M NaOH at 80 C over 100 h
Polymer backbone degradation has a little impact on conductivity
Comparing the ether cleavage degradation of PAEs, the BTMA cation degradation was much slower
Anion conductivity change as a function of time*
Cation Degradation
Membrane: poly(phenylene) based AEM (ATM-PP, SNL) and
crosslinked polystyrene based AEM (AHA, Tokuyama) (cf.
PAE based AEMs became too brittle to handle after 1-2
days); Test conditions: 4 M NaOH (aqueous), no stirring; IEC
measured with back titration
Membrane: Poly(phenylene) based AEM (ATM-PP, SNL) and poly(arylene ether) based
AEM (F-PAE, LANL); Test procedures: 1st step: AEMs were prepared in their salt forms
and were immersed in 0.1 M NaOH at 80 C for 10, 30, 60 and 120 min and followed
by rinsing those in boiling water for 1 h to remove any residual NaOH; 2nd step: AEMs
were immersed in 0.5 M NaOH solution at 80 C for various time intervals
0.1 M NaOH 80oC
Time (min)
0 30 60 90 120
Co
nd
uc
tivit
y (
mS
/cm
)0
20
40
60
80
100
120
140
F-PAE
ATM-PP 3
0.5 M NaOH 80oC
Time (h)
0.1 1 10 100
F-PAE
ATM-PP 3
Time (days)
0 5 10 15 20 25 30
IEC
(m
eq
/g)
0.0
0.5
1.0
1.5
2.0
2.5
ATM-PP 90 C
ATM-PP 60 C
Tokuyama 60 C
4 M NaOH
IEC change as a function of time
2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review
*C. Fujimoto et al. manuscript was submitted 2012
9
Stability Tetramethyl Guanidine Aqueous Solution (ex-situ)
Tetramethylguanidine (TMG) showed electro-catalytic activity; The current at 0.9 V is similar to conventional KOH electrolytes but is less favorable at lower potential due to the probable adsorption to the Pt surface
TMG and its byproducts can adsorb onto the Pt surface below ~0.8 V, obscuring the transition between typical kinetic and mass-limiting regions during oxygen reduction; This effect is especially pronounced at low rpm (low oxygen concentrations)
Highlight: The TMG electrolyte showed remarkable stability after two months, with some signs of increasing resistivity such as the positive potential shift of the H-desorption peak
Oxygen reduction reaction on Pt
ORR study: under O2 sparging with anodic and cathodic scans at a rate of 1 mV/s,
between a potential range of 1.0 V to ~ 0.2 V; A separate set of scans between 1.0
and 0.8 V for the kinetically limited region
H2O redox features of TMG Effect of rpm on oxygen reduction
CV Cycling: 0.0 to 1.1 V RHE (clockwise cycles) in 0.1 M TMG purged with sparging
and blanketing Ar gas; Durability test 2 L of 0.1 M TMG was mixed and allowed to
sit in open air for 2 months
*D. Konopka et al. Electrochem. Solid-State Lett, 15, B17 (2012)
Cation Degradation
2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review
10
Stability of Benzyl and Phenyl Guanidinium (ex-situ)
Benzylpentamethyl guanidinium was slowly decomposed while phenylpentamethyl guanidinium was stable under high pH conditions and elevated temperatures
Highlight: Phenylpentamethyl guanidinium was stable at 4 M NaOH, 90 C for 72 h
Stability of benzylpentamethyl guanidinium*
*M. Hibbs, C. Fujimoto, T. Lambert, D.S. Kim, Y.S. Kim, NAMS 2011, June 6, 2011
Stability of phenylpentamethyl guanidinium*
The relative areas of b and c peaks decrease drastically after NaOH. But b to c area ratio does not change
Cation Degradation
2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review
11
-50
-40
-30
-20
-10
0
10
20
30
Quantum Chemical Modeling for Guanidinium Degradation*
Alpha carbon in benzyl-guanidinium is weak site due to the nucelophilic substitution. Also hydrogen on the alpha carbon is very acidic
Activation energies of center carbon of benzyl and phenyl guanidinium for addition and carbonyl formation are similar
Next: The stability comparison with benzyl tetraalkyl ammonium is under investigation at AIST
*Yoong-Kee Choe, unpublished results, AIST
Benzyl-guanidinium (Addition + Carbonyl formation)
-50
-40
-30
-20
-10
0
10
20
30
Phenyl-guanidinium (Addition + Carbonyl formation)
-10
-5
0
5
10
15
20
12.2 kcal/mol
-20
-10
0
10
20
30
27.5 kcal/mol
28.0 kcal/mol
Benzyl-guanidinium (Nucleophilic substitution) Benzyl-guanidinium (Elimination reaction)
28.0 kcal/mol
Cation Degradation
2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review
12
Current density (A/cm2)
0.0001 0.001 0.01 0.1 1
EiR
-fre
e (
V)
0.80
0.85
0.90
0.95
1.00
1.05
1.10
Initial
after 300 h
Stability Comparison BTMA vs. Phenyl Guanidinium (in-situ)
The stability of phenylpentamethyl guanidinium and benzyltetramethyl ammonium functionalized PAEs were compared when used as ionomer in the catalyst layer
Spectroscopic results indicated that central carbon of pentamethyl guanidinium is the weakest site which is consistent with quantum chemical modeling
Highlight: Phenyl guanidinium cation was substantially more stable than BTMA after 300 h durability test (2 vs. 69 V/dec h)
Durability of ionomer (phenyl guanidinium vs. benzyl ammonium)
Sample IEC (meq./g)
WU (wt.%)
(mS/cm)
M-PAES-TMG 1.0 10 35
F-PAE 2.4 85 100
Cation functionalized ionomers
* Polymers were synthesized from FY 11 tasks
Membrane: Benzyl tetramethyl ammonium functionalized poly(phenylene) (ATM-PP 3, 50 m thick); Catalyst:
Pt black (3 mg/cm2) for anode and cathode; Ionomer for catalyst layer: M-PAES-TMG and F-PAE; testing
conditions: H2/O2 at 60 C; Durability test: Constant voltage of 0.3 V for 300 h
Proposed phenyl pentamethyl guanidinium degradation mechanism
Addition and carbonyl formation Nucelophilic attack to the central carbon
M-PAES-TMG
Current density (A/cm2)
0.0001 0.001 0.01 0.1 1
EiR
-fre
e (
V)
0.80
0.85
0.90
0.95
1.00
1.05
1.10
Initial
after 300 h
Phenyl-guanidinium Benzyl ammonium
Tafel slope degradation rate
2 V/dec h
Tafel slope degradation rate
69 V/dec h
Cation Degradation
2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review
13
Potential/V vs. RHE
0.2 0.4 0.6 0.8 1.0 1.2
Cu
rren
t d
en
sit
y/m
A c
m-2
-3
-2
-1
0
Pt/C, 60 gPt
cm-2
CNT/CNP, 1.0 mg cm
-2
after 5,000 cycles
Stability of Pt and CNT/CNP Composite Catalyst (ex-situ)
Novel CNT/CNP composite catalyst was prepared from nitrogen containing compound and carbon black
Both Pt and CNT/CNP catalyst showed excellent stability under high pH conditions up to after 10,000 potential cycles
The CNT/CNP showed high activity after 5,000 potential cycles (ca. E1/2 = 0.95 V)
Highlight: Durability of electro-catalyst is no issue and the electrochemical activity of CNT/CNP catalyst is excellent
Catalyst ORR activity milestone (E1/2 > 0.9 V) achieved
Carbon Nanotube (CNT)
Carbon Nanoparticle (CNP)
RDE: E-TEK Pt/C, Pt loading: 60 μg cm-2; N-M-C, 1.0 mg cm-2; 0.1 M NaOH; 900 rpm; room temperature; Ag/AgCl (3 M NaCl) reference electrode; steady-state potential
program (OCP for 120 s first, then 20 mV steps, 25 s/step); Cycling: 0.6 -1.0 V, 50 mV s-1, O2-saturated solution
Cycling stability in 0.1 M NaOH
Catalyst Degradation
Potential/ V vs. RHE
0.2 0.4 0.6 0.8 1.0 1.2
Cu
rren
t d
en
sit
y/
mA
cm
-2
-4
-3
-2
-1
0
initial
3,000 cycles
5,000 cycles
Pt/C catalyst (60 g cm-2
)
Potential/ V vs. RHE
0.0 0.2 0.4 0.6 0.8 1.0 1.2Cu
rre
nt
de
ns
ity/
mA
cm
-2
-4
-2
0
2
4
CNT/CNP catalyst (1.0 mg cm-2
)
Potential/V vs. RHE
0.2 0.4 0.6 0.8 1.0 1.2
Cu
rren
t d
en
sit
y/m
A c
m-2
-4
-3
-2
-1
0
Potential/V vs. RHE
0.0 0.2 0.4 0.6 0.8 1.0 1.2Cu
rre
nt
de
nsit
y/ m
A c
m-2
-15
-10
-5
0
5
10
15
Initial
1000 cycles
3000 cycles
5000 cycles
10,000 cycles
Morphology and ORR activity of CNT/CNP catalyst
2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review
14
current density (A/cm2)
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
cell
vo
lt (
V)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
HF
R (
oh
m c
m2)
0.0
0.1
0.2
0.3
0.4
0.5
0.6M-Nafion®-FA-TMG 80C
M-Nafion®-FA-TMG 60C
ATM-PP3 80C
ATM-PP3 60C
H2/O2 AMFC Performance
Membrane electrode assemblies for AMFC were prepared from LANL decal process using the AMFC materials
The MEA using M-Nafion®-FA-TMG showed superior performance to the MEA using ATM-PP 3
Highlight: Maximum power density reached to 577 mW/cm2 at 80 C under H2/O2 conditions
High AMFC performance using hydrocarbon AEM and resonance stabilized perfluorinated ionomer was demonstrated
Ionomer IEC (meq./g)
WU (wt.%)
a
(mS/cm)
HFR (ohm cm2) Maximum Power density (mW/cm2)
60 C 80 C 60 C 80 C
ATM-PP 3 1.7 100 120 0.215 0.174 206 335
M-Nafion®-FA- TMG 0.7 10 20 0.165 0.134 306 577
Materials for MEA fabrication
a measured with hydroxide form at 80 C
H2/O2 initial performance comparison between HC and PF ionomer AEM & hydrocarbon ionomer: ATM-PP 3
PF ionomer: M-Nafion®-FA-TMG
Membrane: BTMA functionalized poly(phenylene) (ATM-PP 3, 50 m thick); Catalyst: Pt black (3 mg/cm2) for
anode and cathode; Ionomer for catalyst layer: M-Nafion-FA-TMG and ATM-PP 3
current density (A/cm2)
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
po
we
r d
en
sit
y (
mW
/cm
2)
0
100
200
300
400
500
600
AMFC Performance & Degradation
2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review
15
60oC
current density (A/cm2)
0.0 0.2 0.4 0.6 0.8 1.0
cell
vo
lt (
V)
0.0
0.2
0.4
0.6
0.8
1.0
HF
R (
oh
m c
m2)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
H2/O
2
H2/Air, CO
2 390 ppm
80oC
current density (A/cm2)
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
ce
ll v
olt
(V
)
0.0
0.2
0.4
0.6
0.8
1.0
HF
R (
oh
m c
m2)
0.0
0.1
0.2
0.3
0.4
0.5
0.6H
2/O
2
H2/Air, CO
2 10 ppm
H2/Air AMFC Performance
H2/CO2 free air AMFC performance showed excellent performance
Additional loss for H2/normal air (CO2 = 390 ppm) conditions was observed; The performance loss was significant at low current region, indicating some water management problems possibly due to the bicarbonate/carbonate issue at lower current density. Further study for the performance loss is required
Highlight: Maximum power density reached to 466 mW/cm2 at 80 C under H2/CO2 free Air conditions
H2/O2 vs. H2/CO2 free Air
Membrane: BTMA functionalized poly(phenylene) (ATM-PP 3, 50 m thick); Catalyst: Pt black (3 mg/cm2) for anode and cathode; Ionomer for catalyst layer: M-Nafion®-FA-TMG
H2/O2 vs. H2/Air
2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review
AMFC Performance & Degradation
16
X Data
0 2 4 6 8 10 12 14 16
cu
rre
nt
de
ns
ity (
A/c
m2)
0.0
0.2
0.4
0.6
0.8
Time (h)
0 2 4 6 8 10 12 14 16
HF
R (
oh
m c
m2)
0.0
0.1
0.2
0.3
0.4
at 0.6 V, 80oC
decay rate: -9.4 mA/cm2 h
decay rate: 2.7 mohm cm2/ h
Durability of BTMA-functionalized Poly(phenylene)s (in-situ)
The AMFC performance degradation depends on cell operating conditions; Large portion of current loss at low voltage conditions is due to water management issue which is recoverable loss.* However, HFR increase mostly reflects the AEM degradation
AEM degradation rate increased with decreasing cell voltage and increasing operating temperature
X Data
0 2 4 6 8 10 12 14 16
cu
rre
nt
de
ns
ity (
A/c
m2)
0.0
0.1
0.2
0.3
0.4
Time (h)
0 2 4 6 8 10 12 14 16
HF
R (
oh
m c
m2)
0.0
0.1
0.2
0.3
0.4
at 0.7 V, 80oC
decay rate: -2.5 mA/cm2 h
decay rate: 1.0 mohm cm2/ h
H2/O2, 80 C at 0.7 V
Membrane: BTMA functionalized poly(phenylene) (ATM-PP 3, 50 m thick); Catalyst: Pt black (3 mg/cm2) for anode and cathode; Ionomer for catalyst layer: M-Nafion®-FA-
TMG; Life test conditions: constant voltage under full hydration
X Data
0 2 4 6 8 10 12 14 16
cu
rre
nt
de
ns
ity (
A/c
m2)
0.0
0.1
0.2
0.3
0.4
0.5
Time (h)
0 2 4 6 8 10 12 14 16
HF
R (
oh
m c
m2)
0.0
0.2
0.4
0.6
0.8
at 0.4 V, 95oC
decay rate: -19.0 mA/cm2 h
decay rate: 12.1 mohm cm2/ h
H2/Air, 95 C at 0.4 V H2/O2, 80 C at 0.6 V
*see supporting information
2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review
AMFC Performance & Degradation
17
AMFC Degradation Summary
In general, the degradation rate of AMFC materials was faster under ex-situ conditions than under in-situ test; however other degradations such as membrane-electrode interface or water management issue played greater role in in-situ AMFC testing
Highlight: Materials developed from this project (appeared in yellow box) showed at least comparable durability to the state-of- the-art AMFC materials
Compo-nent
Type Degradation* (time, NaOH, Temp.)
Slide page
Polymer
Poly(arylene ether) Aryl ether linkage
Fast (g) (< 1 h, 0.5M, 80 C)
5
Poly(phenylene) Stable 5
Perfluorinated Stable 7
Amide linkage Slow (g) (72h, 0.5M, 80 C)
7
Cation
Tetramethyl guanidine aqueous soln.
Slow (g) (2 month, TMG 0.1 M, 25 C)
9
Benzyl tetra methylammonium
Slow (g) (< 100 h, 0.5 M, 80 C)
8
Sulfone penta methyl guanidinium
Fast (g) (< 1 h, 0.5 M, 80 C)
7
Benzyl penta methyl guanidinium
Moderate (g) (24 h 1M, 25 C)
10
Phenyl penta methyl guanidinium
Stable 10
Electro-catalyst
Platinum/carbon Stable 13
CNT/CNP Stable 13
Ex-situ testing in NaOH aqueous solution
Component Type Degradation (time, Temp.)
Slide page
Polymer
Poly(arylene ether) Moderate (c) (55h, 80 C)
6
Poly(phenylene) Stable 6
Cation
Benzyl tetramethyl ammonium (AEM)
moderate (g) (100h, 80 C)
16
Benzyl tetramethyl ammonium (ionomer)
Slow (g) (< 100h, 80 C)
12
Phenyl pentamethyl guanidinium (ionomer)
Slow (g) (72h, 90 C)
12
AEM-electrode interface
AEM with Mw < 100 K Unstable (c) 6
AEM with Mw > 100 K Stable 6
Electro-catalyst Platinum/carbon Stable 13
CNT/CNP Stable 13
Water management*
Hydrocarbon ionomer Fast (g) S
Perfluorinated ionomer Moderate (g)
In-situ AMFC testing
*g: gradual loss; c: catastrophic loss
18
Relevance: Alkaline membrane fuel cells may enable non-precious metal catalysts and avoid or mitigate the shortcomings of traditional liquid AFCs
Approach: Develop highly stable and conductive anion exchange polymer electrolytes using resonance stabilized guanidinium cations and perfluorinated ionomer
Technical Accomplishments and Progress:
Demonstrated good H2/O2 and H2/air AMFC performance (> 450 and 550 mW/cm2, respectively) at 80 C
Established several synthetic pathways to prepare stable anion exchange polymer electrolytes and carbon based non-precious metal catalysts
Explored degradation phenomena for polymer backbones, cations and ionomers and ranked the stability both under ex-situ and in-situ conditions
Technology Transfer/Collaborations: Active partnership with Ovonic Fuel Cells and Cellera Inc.; Several patent applications were filed for technology transfer
Proposed Future Research: Catalyst-ionomer interaction and further improvement on stability, conductivity and mechanical properties of polymer electrolytes
2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review
Project Summary
19 2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review
Technical Back-Up Slides
20
Decoupling Degradation from in-situ AMFC testing AMFC Durability
2012 US DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review
0 5 10 15 20 25 30
cu
rre
nt
de
nsit
y (
A/c
m2)
0.0
0.1
0.2
0.3
0.4
Time (h)
0 5 10 15 20 25 30
HF
R (
oh
m c
m2)
0.0
0.1
0.2
0.3
0.4
1. Unrecoverable loss
2. Recoverable loss
3. Catastrophic failure
4. Unrecoverable loss(AEM related)
5. Recoverable loss(AEM related)
6. Catastrophic failure(AEM related)
1. Unrecoverable loss includes:
AEM degradation, ionomer degradation, catalyst degradation and interfacial degradation; AEM and ionomer cation degradation are the major contributors
2. Recoverable loss includes:
AEM dehydration and local flooding depending on operating conditions
3. Catastrophic failure is mostly due to:
AEM backbone failure (this failure accompanied by OCV decrease)
4. Unrecoverable loss (AEM related) includes:
AEM degradation and interfacial degradation: In all cases with few exception, AEM degradation
5. Recoverable loss (AEM related) is due to:
AEM dehydration
6. Catastrophic failure is mostly due to:
AEM backbone failure (this failure accompanied by OCV decrease)
Separated from current density and HFR behavior, the Ionomer degradation rate was measured from Tafel slope change
AMFC extended term test example General observation & in-situ methodology