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Los Alamos National Laboratory
Catalyst-ionomer Interactions/AMFC Durability
Yu Seung Kim
MPA-11: Materials Synthesis and Integrated Devices, Los Alamos National Laboratory, Los
Alamos, New Mexico, 87545 USA
Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA
2019 Anion Exchange Membrane Workshop∣ May 30, 2019 ∣ Sheraton Dallas Hotel, Dallas, TX
Los Alamos National Laboratory
6/12/2019 | 2
Acknowledgment
Cy Fujimoto (Polymer synthesis,SNL)
Dongguo Li (Electrochemistry)
Albert Lee(Characterization)
Sandip Maurya(Device testing)
Sarah Park(Synthesis)
CollaboratorsChulsung Bae (RPI)Ivana Gonzales (UNM)Michael Hibbs (SNL)Daniel Leonard (LANL)Joseph Dumont (LANL)Rex Hjelm (former LANL)
NIST neutron centerLANSCE neutron center
FundingDOE EERE FCTO
Los Alamos National Laboratory
6/12/2019 | 3
LANL Project funded by DOE FCTOResearch Focus Major Founding
AEMStability(2016)
Polymer backbone degradation1
AEMFCPerformance(2017-2019)
Phenyl group adsorption2
Cation-hydroxide-water co-adsorption3
AEMFCDurability
(2019)
Oxidation of phenyl group (in the cathode ionomer)Degradation of ammonium group (in the anode ionomer)
1Fujimoto et al. J. Memb. Sci. 423-424, 438-449, 2012; 2Matanovic et al. J. Phy. Chem. Let. 8, 4918-4924, 2017; 3Li et al. Cur. Opinion in Electrochem., 12, 189-195, 2018; 4S. Murya, S. Energy & Environ.
Sci. 11, 3283-3291, 2019
Los Alamos National Laboratory
6/12/2019 | 4
Catalyst-Ionomer Interactions
Los Alamos National Laboratory
6/12/2019 | 5
Adsorption of ionomer fragment on electrocatalysts
Li et al. Curr. Opin. Electrochem. 12, 189-195 (2018)
QA OH
Anion exchange ionomer
Backbone phenyl
Sidechain phenyl
Electrocatalyst
Cationic group
Adsorption energy calculated by DFT
Those adsorptions are unique phenomena for alkaline ionomer because acid system
uses perfluorosulfonic acid.
Los Alamos National Laboratory
6/12/2019 | 6
Impact of phenyl adsorption on HOR catalyst on AMFC performance
Los Alamos National Laboratory
6/12/2019 | 7
Identification of phenyl group adsorption on Pt at HOR potential
Matanovic et al. J. Phys. Chem. Lett. 8, 4918 (2017)
TMAOH BTMAOH
NOH N OH
E / V vs. RHE-0.05 0.00 0.05 0.10 0.15 0.20
i / m
A cm
-2 ge
o
-2
-1
0
1
2
0.1 M TMAOH0.1 M BTMAOH
HOR voltammogram of Pt/C (RDE experiment)
Electric field [V/A]-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6
Ead
,fiel
d [eV
]
-4
-3
-2
-1
0
ΔE=-2.30 eV ΔE=-2.15 eV ΔE=-1.51 eV ΔE=-2.15 eV
Adsorption Position (side view) of BTMA on Pt(111) at U = 0 V
Effect of Applied Potential on the Interaction
Conformational change
U = 3Å x Efield
Los Alamos National Laboratory
6/12/2019 | 8
Impact of backbone phenyl adsorption on HOR of Pt
Potential (V vs. RHE)0.0 0.2 0.4 0.6 0.8 1.0
Cur
rent
Den
sity
* (m
A cm
-2ge
o)
-2
-1
0
1
2
N OH
Potential (V vs. RHE)
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Cur
rent
Den
sity
* (m
A cm
-2)
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
N
N
Phenyl adsorption
Phenyl Desorption due tocation adsorption
Phenyl adsorption from polymer backbone
BTMAOH phenyl adsorption Ionomer phenyl adsorption
• Backbone phenyl impacts the HOR up to 0.8 V vs. RHE, more significant than ammonium
functionalized phenyl group. Maurya et al. Chem. Mater. 30, 2188 (2018)Matanovic et al. J. Phys. Chem. Lett. 8, 4918 (2017)
Los Alamos National Laboratory
6/12/2019 | 9
Impact of ionomer type on HOR of Pt
Poly(phenylene)(2012 SNL)
F2C
F2CO
FC CF3
OCF2
CF2
COHN N C
N
N
F2C
F2C
OH
N
N
Perfluorinated(2013 LANL)
Polyolefinic(2018 LANL)
Potential (V vs. RHE)
0.0 0.2 0.4 0.6 0.8 1.0
Cur
rent
den
sity
(mA
cm
-2no
rm)
-0.25
0.00
0.25
0.50
0.75
1.00
1.25
Loss due to the backbone phenylgroup adsorption
Pt/C
N NH
n
OH
• As the number of ammonium unsubstituted phenyl group increased, the HOR activity
decreases.
Pt microelectrode in contact with quaternized polymers
Maurya et al. Chem. Mater. 30, 2188 (2018)
Los Alamos National Laboratory
6/12/2019 | 10
The adsorption energy of polymer backbone phenyl fragment on Pt(111) by DFT calculation
Fragment Ead (eV) rank
fluorene -1.38 1o-terphenyl -1.52 2benzene* -1.95 3biphenyl ether -2.19 4biphenyl -2.87 5m-terphenyl -3.61 6p-terphenyl -3.94 7
Adsorption energies (in eV) using optPBE-vdW
Benzene
BiphenylO
Biphenyl ether
p-terphenyl
m-terphenyl
o-terphenylFluorene
Matanovic et al. Chem. Mater. in press (2019)
Los Alamos National Laboratory
6/12/2019 | 11
Impact of phenyl group adsorption on AMFC performance
CF3 CF3
N
n 1-n
OH
Quaternized poly(biphenyl alkylene)
n = 1BPN100
n = 0.45BPN45
Quaternized poly(terphenyl alkylene)
CF3
NOHp-TPN
F3C
NOHm-TPN
CF3CF3
.45 .55
Quaternized polyfluorene
FLN55
N N OHOH
Matanovic et al. Chem. Mater. in press (2019)
AMFC performance of MEAs using different ionomers
Courtesy: Prof. Bae at RPI
Los Alamos National Laboratory
6/12/2019 | 12
Impact of phenyl adsorption on ORR and OER catalysts on AMFC and
AEM electrolyzer durability
Los Alamos National Laboratory
6/12/2019 | 13
Discovery of the impact of phenyl adsorption on ORR or OER durability
• An MEA using less phenyl adsorbing ionomer (FLN) showed better AMFC durability
AMFC current density change of
two MEAs (only cathode ionomer
is different)
Los Alamos National Laboratory
6/12/2019 | 14
Identification of phenyl group adsorption on Pt at ORR potential
N+
OH- N+
OH-
OHHO
Ar
BCC
A
1.0 V vs. RHE
ORR current changes, CV, ORR voltammograms and 1H NMR analysis of BTMAOH
Los Alamos National Laboratory
6/12/2019 | 15
Detection of the phenol group formation from cathode ionomer1H NMR analysis of cathode ionomer (BPN) after 75 hours of AMFC operation at 0.9 V
CF3
N+ OH-
Oxidation CF3
N+OH-
OH*
* *
a)
b)
Ar
ab
cd
e
f
g
BPN
1H NMR analysis of cathode ionomer (FLN) after 230 h hours of AMFC operation at 0.9 V
N+ N+OH
-OH-
CF3 CF3
OH * * *
N+ N+OH
-OH-
CF3 CF3 Oxidation
4 44 4
ga
DMFH2O
a
bce
d
f ddd
g
g
DMSO-d6
• Phenyl oxidation for BPN: 1.3% after 75 h vs. 0.34% after 230 hMaurya et al. Manuscript under review, J. Power Sources (2019)
Los Alamos National Laboratory
6/12/2019 | 16
Phenyl oxidation at OER potential (AEM electrolysis)
a)
(1) parallel (2) lying (3) standing
Ar
DMSO-d6
cb
dfeH2O
a
F3C
N+ OH-
Ara
b
dc
f
e
b)
Initial
After 100 h
g
F3C
N+OH
-
OH
* *g
5.8 5.7 5.6
ppm
Initial
After 100 h
a)
Inset figure
at 2.1 V
Phenyl adsorption energy (DFT calculation) iV curves of IrO2 catalyzed AEM electrolyzer
• PGM catalysts have high phenyl adsorption energy and the AEM electrolyzer using the
OER catalysts showed performance decay.Li et al. ACS Appl. Mater. Interf. 11, 9696-9701 (2019)
3% conversion
Los Alamos National Laboratory
6/12/2019 | 17
Take-home message for phenyl oxidation
OER catalyst
Electrochemical oxidation &
phenol formation
At 2.1 V
Performance decay of AEM electrolyzer over time
Step 2
Effect of pH on Pt ORR activityDegradation mechanism
• The concentration of phenol at the catalyst-ionomer interface is much higherthan that in the bulk ionomer.
• The impact is similar to carbonation but this brings permanent damage to the cellmore significant than carbonation.
Los Alamos National Laboratory
6/12/2019 | 18
Impact of cation adsorption on HOR catalysts on AMFC performance
Los Alamos National Laboratory
6/12/2019 | 19
Identification of cation adsorption on Pt at HOR potential
E /V vs. RHE
-0.1 0.0 0.1 0.2 0.3 0.4 0.5
i /m
A cm
-2
-0.5
0.0
0.5
1.0
1.5
2.0
initial
TMAOH after 0.1 V / 120 min
Time / min
0 20 40 60 80 100 120
i / m
A cm
-2ge
o
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
TMAOH
HClO4
HOR voltammogram of Pt/C in 0.1 M TMAOH
Chronoamperometry at 0.1 V vs. RHE
• HOR activity of Pt in TMAOH decreases after exposure the electrode at 0.1 V vs. RHEChung et al. J. Electrochem. Soc. 163, F1503-F1509 (2019)
Los Alamos National Laboratory
6/12/2019 | 20
Detection of TMA-water co-adsorption on Pt at 0.1 V vs. RHE
IRRAS in the (a) fingerprint and (b) O-H stretching regions duringchronoamperometry of Pt in 0.1 M TMAOH
• Time-dependent cation adsorption on Pt at 0.1 V vs. RHE.• OH stretching region indicates that the co-adsorbed layer
has high concentration of cationic group vs. water.
Chung et al. J. Phys. Chem. Lett. 7, 4464-4469 (2016)
Wavenumber / cm-1
9001000110012001300140015001600
Abso
rban
ce
TMAOH soln.
Initial
15 min
55 min
as(CH3)
s(CH3)
as(C-N)
Pt surfacea)
Wavenumber / cm-1
2400260028003000320034003600
Abso
rban
ce
as,s(OHwater) as,s(OHhdroxide)
b)
TMAOH soln.
Initial
15 min
55 minPt surface
0.1 M TMAOH0.1 M TMAOH
Harmon et al. J. Mol. Struc. 159, 255-263 (1987)
TMAOH: pentahydrate
trihydrate
dihydrate
monohydrate
FTIR of highly conc. TMAOH
Los Alamos National Laboratory
6/12/2019 | 21
Impact of co-adsorption on hydrogen diffusionH2 permeability in H2SO4 and KOH as afunction of the concentration.
Ruetschi J. Electrochem. Soc.114, 301 (1967)
Concentration (M)
0 2 4 6 8 10 12 14 16
H2 p
erm
eabi
lity
(S*D
)
0.1
1
10
100
H2SO4
KOH
AEM (thickness): quaternized poly(terphenylene) (35 µm), ionomer:BPN, anode catalyst: PtRu/C (0.75 mgmetal cm-2) cathode catalyst: Pt/C(0.6 mgmetal cm-2), cathode flow rate: 300 sccm of O2.
Impact of anode flow rate on AMFCperformance
Li et al. Curr. Opin. Electrochem. 12, 189-195 (2018)
Los Alamos National Laboratory
6/12/2019 | 22
Anode ionomer design aspect towards highly-performing AMFCs
Park et al. unpublished (2019)
n
CF3
N
(b) o-BTN (c) TEA-o-BTN
n
CF3
N
n
CF3
N
(a) BPN
Current density (A cm-2)
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
Cel
l vol
tage
(V)
0.0
0.2
0.4
0.6
0.8
1.0 TEA-o-BTN (2,000 sccm H2)TEA-o-BTN (500 sccm H2)o-BTN (500 sccm H2)BTN (500 sccm H2)
80 °C
Increase fractional
free volume
Decrease adsorption
energy
Temperature (°C)
Diffusion coefficient / (10-9 m2 s-1)BPN o-BPN Fold increase
25 2.69 8.00 3.0
40 3.24 12.45 3.8
65 3.78 17.58 4.7
80 4.45 22.30 5.0
Table. Self-diffusion coefficients of H2 in BPN and o-BTN dispersions by PFG 1H NMR
Impact of anode ionomer structure on AMFC performance
• Impact of the cationic group ismore significant Researchneed
Los Alamos National Laboratory
6/12/2019 | 23
Impact of cation adsorption on HOR catalysts on AMFC Durability
Los Alamos National Laboratory
6/12/2019 | 24
Motivation of cation co-adsorption on AMFC durability
• The concentration of the TMAOH in the co-adsorbed layer calculated from scattering length density is unusually high: the ratio of TMAOH to water = 5:1
(The highest TMAOH to water ratio in the aqueous solution is 1:1)
Schematic illustration of co-adsorbed layer structure on Pt after 12 h exposure at 0.1 V vs. RHE
Neutron reflectometry electrochemical cell*
Dumont et al. unpublished data (2019)
Los Alamos National Laboratory
6/12/2019 | 25
Hour (h)
0 20 40 60 80 100 120 140
Curr
ent d
ensi
ty (A
cm
-2)
0.00
0.01
0.02
0.03
0.04
0.05
0.06
Hour (h)0 20 40 60 80
HFR
( c
m2 )
0.0
0.1
0.2
0.3
0.4
at 80 °C, 0.9 V
Impact of coadsorption on AMFC lifeCurrent density change at 0.9 V
Anode: FLN, Cathode: FLNboth are phenyl non-adsorbing
Los Alamos National Laboratory
6/12/2019 | 26
The ionomer degradation due to the cation co-adsorption
CF3
N+ OH-
Oxidation
N
Hoffman Elimination
CF3
N+ OH-
* *
HO *
* *
CF3
f
Ar
ab
cd
e
g
hi
j
Note: * are also possible oxidation sites
Anode Side
Cathode
g
f
Ar
a bcde
DMSO-d6
hij• Cathode ionomer degradation = 30% of the
aromatic groups via phenyl oxidation.• Anode ionomer degradation = 27% of the TMA
cationic groups via Hoffman Elimination.
After AMFC running for 100 h at 0.9 V
Lee et al. unpublished data (2019)
Los Alamos National Laboratory
6/12/2019 | 27
Water management issue driven by the co-adsorption
Maurya et al. unpublished data (2019)
n
CF3
N
(b) o-BTN (c) TEA-o-BTN
n
CF3
Nn
CF3
N
(a) BPN
80 °C, 600 mA/cm2
Time (hour)
0 20 40 60 80 100
HFR
(Ohm
cm
2 )
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14BTNo-BTNTEA-o-BTN
80 °C, 600 mA/cm2
Time (hour)
0 20 40 60 80 100
Cur
rent
den
sity
(A/c
m2 )
0.0
0.2
0.4
0.6
0.8
1.0
BPNo-BTNTEA-o-BTN
Cell voltage change at 0.6 A/cm2 HFR change at 0.6 A/cm2
Cel
l vol
tage
(V)
Los Alamos National Laboratory
6/12/2019 | 28
Summary
AMFC anode performance
AMFC cathodedurability
AMFC anode performance
AMFC anodedurability
AEM electrolyzer
anodedurability
Los Alamos National Laboratory
6/12/2019 | 29
Electrode performance discussion• Subject
• Ionomer performance• Low PGM performance• Non PGM performance• Electrode processing• Liquid electrolyte
• Area• Fuel cells (HOR and ORR)• Electrolyzers (HER and OER)